| Message ID | 20231205053509.2342169-4-vivek.kasireddy@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/gup: Introduce memfd_pin_user_pages() for pinning memfd pages (v6) | expand |
On 05.12.23 06:35, Vivek Kasireddy wrote: > For drivers that would like to longterm-pin the pages associated > with a memfd, the pin_user_pages_fd() API provides an option to > not only pin the pages via FOLL_PIN but also to check and migrate > them if they reside in movable zone or CMA block. This API > currently works with memfds but it should work with any files > that belong to either shmemfs or hugetlbfs. Files belonging to > other filesystems are rejected for now. > > The pages need to be located first before pinning them via FOLL_PIN. > If they are found in the page cache, they can be immediately pinned. > Otherwise, they need to be allocated using the filesystem specific > APIs and then pinned. > > v2: > - Drop gup_flags and improve comments and commit message (David) > - Allocate a page if we cannot find in page cache for the hugetlbfs > case as well (David) > - Don't unpin pages if there is a migration related failure (David) > - Drop the unnecessary nr_pages <= 0 check (Jason) > - Have the caller of the API pass in file * instead of fd (Jason) > > v3: (David) > - Enclose the huge page allocation code with #ifdef CONFIG_HUGETLB_PAGE > (Build error reported by kernel test robot <lkp@intel.com>) > - Don't forget memalloc_pin_restore() on non-migration related errors > - Improve the readability of the cleanup code associated with > non-migration related errors > - Augment the comments by describing FOLL_LONGTERM like behavior > - Include the R-b tag from Jason > > v4: > - Remove the local variable "page" and instead use 3 return statements > in alloc_file_page() (David) > - Add the R-b tag from David > > v5: (David) > - For hugetlb case, ensure that we only obtain head pages from the > mapping by using __filemap_get_folio() instead of find_get_page_flags() > - Handle -EEXIST when two or more potential users try to simultaneously > add a huge page to the mapping by forcing them to retry on failure > > v6: (Christoph) > - Rename this API to memfd_pin_user_pages() to make it clear that it > is intended for memfds > - Move the memfd page allocation helper from gup.c to memfd.c > - Fix indentation errors in memfd_pin_user_pages() > - For contiguous ranges of folios, use a helper such as > filemap_get_folios_contig() to lookup the page cache in batches > > Cc: David Hildenbrand <david@redhat.com> > Cc: Christoph Hellwig <hch@infradead.org> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch> > Cc: Mike Kravetz <mike.kravetz@oracle.com> > Cc: Hugh Dickins <hughd@google.com> > Cc: Peter Xu <peterx@redhat.com> > Cc: Gerd Hoffmann <kraxel@redhat.com> > Cc: Dongwon Kim <dongwon.kim@intel.com> > Cc: Junxiao Chang <junxiao.chang@intel.com> > Suggested-by: Jason Gunthorpe <jgg@nvidia.com> > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> (v2) > Reviewed-by: David Hildenbrand <david@redhat.com> (v3) > Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com> > --- > include/linux/memfd.h | 5 +++ > include/linux/mm.h | 2 + > mm/gup.c | 102 ++++++++++++++++++++++++++++++++++++++++++ > mm/memfd.c | 34 ++++++++++++++ > 4 files changed, 143 insertions(+) > > diff --git a/include/linux/memfd.h b/include/linux/memfd.h > index e7abf6fa4c52..6fc0d1282151 100644 > --- a/include/linux/memfd.h > +++ b/include/linux/memfd.h > @@ -6,11 +6,16 @@ > > #ifdef CONFIG_MEMFD_CREATE > extern long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int arg); > +extern struct page *memfd_alloc_page(struct file *memfd, pgoff_t idx); > #else > static inline long memfd_fcntl(struct file *f, unsigned int c, unsigned int a) > { > return -EINVAL; > } > +static inline struct page *memfd_alloc_page(struct file *memfd, pgoff_t idx) > +{ > + return ERR_PTR(-EINVAL); > +} > #endif > > #endif /* __LINUX_MEMFD_H */ > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 418d26608ece..ac69db45509f 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2472,6 +2472,8 @@ long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages, > struct page **pages, unsigned int gup_flags); > long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages, > struct page **pages, unsigned int gup_flags); > +long memfd_pin_user_pages(struct file *file, pgoff_t start, > + unsigned long nr_pages, struct page **pages); > > int get_user_pages_fast(unsigned long start, int nr_pages, > unsigned int gup_flags, struct page **pages); > diff --git a/mm/gup.c b/mm/gup.c > index 231711efa390..eb93d1ec9dc6 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -5,6 +5,7 @@ > #include <linux/spinlock.h> > > #include <linux/mm.h> > +#include <linux/memfd.h> > #include <linux/memremap.h> > #include <linux/pagemap.h> > #include <linux/rmap.h> > @@ -17,6 +18,7 @@ > #include <linux/hugetlb.h> > #include <linux/migrate.h> > #include <linux/mm_inline.h> > +#include <linux/pagevec.h> > #include <linux/sched/mm.h> > #include <linux/shmem_fs.h> > > @@ -3410,3 +3412,103 @@ long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages, > &locked, gup_flags); > } > EXPORT_SYMBOL(pin_user_pages_unlocked); > + > +/** > + * memfd_pin_user_pages() - pin user pages associated with a memfd > + * @memfd: the memfd whose pages are to be pinned > + * @start: starting memfd offset > + * @nr_pages: number of pages from start to pin > + * @pages: array that receives pointers to the pages pinned. > + * Should be at-least nr_pages long. > + * > + * Attempt to pin pages associated with a memfd; given that a memfd is either > + * backed by shmem or hugetlb, the pages can either be found in the page cache > + * or need to be allocated if necessary. Once the pages are located, they are > + * all pinned via FOLL_PIN. And, these pinned pages need to be released either > + * using unpin_user_pages() or unpin_user_page(). > + * > + * It must be noted that the pages may be pinned for an indefinite amount > + * of time. And, in most cases, the duration of time they may stay pinned > + * would be controlled by the userspace. This behavior is effectively the > + * same as using FOLL_LONGTERM with other GUP APIs. > + * > + * Returns number of pages pinned. This would be equal to the number of > + * pages requested. If no pages were pinned, it returns -errno. > + */ > +long memfd_pin_user_pages(struct file *memfd, pgoff_t start, > + unsigned long nr_pages, struct page **pages) > +{ > + pgoff_t start_idx, end_idx = start + nr_pages - 1; > + unsigned int flags, nr_folios, i, j; > + struct folio_batch fbatch; > + struct page *page = NULL; > + struct folio *folio; > + long ret; > + > + if (!nr_pages) > + return -EINVAL; > + > + if (!memfd) > + return -EINVAL; > + > + if (!shmem_file(memfd) && !is_file_hugepages(memfd)) > + return -EINVAL; > + > + flags = memalloc_pin_save(); > + do { > + folio_batch_init(&fbatch); > + start_idx = start; > + i = 0; > + > + while (start_idx <= end_idx) { > + /* > + * In most cases, we should be able to find the page > + * in the page cache. If we cannot find it for some > + * reason, we try to allocate one and add it to the > + * page cache. > + */ > + nr_folios = filemap_get_folios_contig(memfd->f_mapping, > + &start_idx, > + end_idx, > + &fbatch); > + if (page) { > + put_page(page); > + page = NULL; > + } > + for (j = 0; j < nr_folios; j++) { > + folio = fbatch.folios[j]; > + ret = try_grab_page(&folio->page, FOLL_PIN); > + if (unlikely(ret)) { > + folio_batch_release(&fbatch); > + goto err; > + } > + > + pages[i++] = &folio->page; > + } I might be wrong, but that interface is still inconsistent. I think your intention is to always return folios (head pages), but why are we returning pages from this interface then? It would be more consistent regarding the other GUP interfaces to return the actual tail pages that fit the given "pgoff_t start". So if you punch in "nr_pages" you expect to get "nr_pages" pages, and not some other number of folios. Otherwise, this interface is highly confusing. If you always want to return folios, then better name it "memfd_pin_user_folios" (or just "memfd_pin_folios") and pass in a range (instead of a nr_pages parameter), and somehow indicate to the caller how many folio were in that range, and if that range was fully covered. Or am I missing something?
Hi, > > +struct page *memfd_alloc_page(struct file *memfd, pgoff_t idx) > > +{ > > +#ifdef CONFIG_HUGETLB_PAGE > > + struct folio *folio; > > + int err; > > + > > + if (is_file_hugepages(memfd)) { > > + folio = alloc_hugetlb_folio_nodemask(hstate_file(memfd), > > + NUMA_NO_NODE, > > + NULL, > > + GFP_USER); > > + if (folio && folio_try_get(folio)) { > > + err = hugetlb_add_to_page_cache(folio, > > If alloc_hugetlb_folio_nodemask moved out of the CONFIG_HUGETLB_PAGE > ifdef, the ifdef here could go away. Unlike alloc_hugetlb_folio_nodemask(), hugetlb_add_to_page_cache() does not get exposed without enabling CONFIG_HUGETLB_PAGE. > > Either way, this looks good: > > Reviewed-by: Christoph Hellwig <hch@lst.de> Thank you for the review. Thanks, Vivek > >
Hi David, > On 05.12.23 06:35, Vivek Kasireddy wrote: > > For drivers that would like to longterm-pin the pages associated > > with a memfd, the pin_user_pages_fd() API provides an option to > > not only pin the pages via FOLL_PIN but also to check and migrate > > them if they reside in movable zone or CMA block. This API > > currently works with memfds but it should work with any files > > that belong to either shmemfs or hugetlbfs. Files belonging to > > other filesystems are rejected for now. > > > > The pages need to be located first before pinning them via FOLL_PIN. > > If they are found in the page cache, they can be immediately pinned. > > Otherwise, they need to be allocated using the filesystem specific > > APIs and then pinned. > > > > v2: > > - Drop gup_flags and improve comments and commit message (David) > > - Allocate a page if we cannot find in page cache for the hugetlbfs > > case as well (David) > > - Don't unpin pages if there is a migration related failure (David) > > - Drop the unnecessary nr_pages <= 0 check (Jason) > > - Have the caller of the API pass in file * instead of fd (Jason) > > > > v3: (David) > > - Enclose the huge page allocation code with #ifdef > CONFIG_HUGETLB_PAGE > > (Build error reported by kernel test robot <lkp@intel.com>) > > - Don't forget memalloc_pin_restore() on non-migration related errors > > - Improve the readability of the cleanup code associated with > > non-migration related errors > > - Augment the comments by describing FOLL_LONGTERM like behavior > > - Include the R-b tag from Jason > > > > v4: > > - Remove the local variable "page" and instead use 3 return statements > > in alloc_file_page() (David) > > - Add the R-b tag from David > > > > v5: (David) > > - For hugetlb case, ensure that we only obtain head pages from the > > mapping by using __filemap_get_folio() instead of find_get_page_flags() > > - Handle -EEXIST when two or more potential users try to simultaneously > > add a huge page to the mapping by forcing them to retry on failure > > > > v6: (Christoph) > > - Rename this API to memfd_pin_user_pages() to make it clear that it > > is intended for memfds > > - Move the memfd page allocation helper from gup.c to memfd.c > > - Fix indentation errors in memfd_pin_user_pages() > > - For contiguous ranges of folios, use a helper such as > > filemap_get_folios_contig() to lookup the page cache in batches > > > > Cc: David Hildenbrand <david@redhat.com> > > Cc: Christoph Hellwig <hch@infradead.org> > > Cc: Daniel Vetter <daniel.vetter@ffwll.ch> > > Cc: Mike Kravetz <mike.kravetz@oracle.com> > > Cc: Hugh Dickins <hughd@google.com> > > Cc: Peter Xu <peterx@redhat.com> > > Cc: Gerd Hoffmann <kraxel@redhat.com> > > Cc: Dongwon Kim <dongwon.kim@intel.com> > > Cc: Junxiao Chang <junxiao.chang@intel.com> > > Suggested-by: Jason Gunthorpe <jgg@nvidia.com> > > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> (v2) > > Reviewed-by: David Hildenbrand <david@redhat.com> (v3) > > Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com> > > --- > > include/linux/memfd.h | 5 +++ > > include/linux/mm.h | 2 + > > mm/gup.c | 102 ++++++++++++++++++++++++++++++++++++++++++ > > mm/memfd.c | 34 ++++++++++++++ > > 4 files changed, 143 insertions(+) > > > > diff --git a/include/linux/memfd.h b/include/linux/memfd.h > > index e7abf6fa4c52..6fc0d1282151 100644 > > --- a/include/linux/memfd.h > > +++ b/include/linux/memfd.h > > @@ -6,11 +6,16 @@ > > > > #ifdef CONFIG_MEMFD_CREATE > > extern long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int > arg); > > +extern struct page *memfd_alloc_page(struct file *memfd, pgoff_t idx); > > #else > > static inline long memfd_fcntl(struct file *f, unsigned int c, unsigned int a) > > { > > return -EINVAL; > > } > > +static inline struct page *memfd_alloc_page(struct file *memfd, pgoff_t > idx) > > +{ > > + return ERR_PTR(-EINVAL); > > +} > > #endif > > > > #endif /* __LINUX_MEMFD_H */ > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > index 418d26608ece..ac69db45509f 100644 > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -2472,6 +2472,8 @@ long get_user_pages_unlocked(unsigned long > start, unsigned long nr_pages, > > struct page **pages, unsigned int gup_flags); > > long pin_user_pages_unlocked(unsigned long start, unsigned long > nr_pages, > > struct page **pages, unsigned int gup_flags); > > +long memfd_pin_user_pages(struct file *file, pgoff_t start, > > + unsigned long nr_pages, struct page **pages); > > > > int get_user_pages_fast(unsigned long start, int nr_pages, > > unsigned int gup_flags, struct page **pages); > > diff --git a/mm/gup.c b/mm/gup.c > > index 231711efa390..eb93d1ec9dc6 100644 > > --- a/mm/gup.c > > +++ b/mm/gup.c > > @@ -5,6 +5,7 @@ > > #include <linux/spinlock.h> > > > > #include <linux/mm.h> > > +#include <linux/memfd.h> > > #include <linux/memremap.h> > > #include <linux/pagemap.h> > > #include <linux/rmap.h> > > @@ -17,6 +18,7 @@ > > #include <linux/hugetlb.h> > > #include <linux/migrate.h> > > #include <linux/mm_inline.h> > > +#include <linux/pagevec.h> > > #include <linux/sched/mm.h> > > #include <linux/shmem_fs.h> > > > > @@ -3410,3 +3412,103 @@ long pin_user_pages_unlocked(unsigned long > start, unsigned long nr_pages, > > &locked, gup_flags); > > } > > EXPORT_SYMBOL(pin_user_pages_unlocked); > > + > > +/** > > + * memfd_pin_user_pages() - pin user pages associated with a memfd > > + * @memfd: the memfd whose pages are to be pinned > > + * @start: starting memfd offset > > + * @nr_pages: number of pages from start to pin > > + * @pages: array that receives pointers to the pages pinned. > > + * Should be at-least nr_pages long. > > + * > > + * Attempt to pin pages associated with a memfd; given that a memfd is > either > > + * backed by shmem or hugetlb, the pages can either be found in the page > cache > > + * or need to be allocated if necessary. Once the pages are located, they > are > > + * all pinned via FOLL_PIN. And, these pinned pages need to be released > either > > + * using unpin_user_pages() or unpin_user_page(). > > + * > > + * It must be noted that the pages may be pinned for an indefinite amount > > + * of time. And, in most cases, the duration of time they may stay pinned > > + * would be controlled by the userspace. This behavior is effectively the > > + * same as using FOLL_LONGTERM with other GUP APIs. > > + * > > + * Returns number of pages pinned. This would be equal to the number of > > + * pages requested. If no pages were pinned, it returns -errno. > > + */ > > +long memfd_pin_user_pages(struct file *memfd, pgoff_t start, > > + unsigned long nr_pages, struct page **pages) > > +{ > > + pgoff_t start_idx, end_idx = start + nr_pages - 1; > > + unsigned int flags, nr_folios, i, j; > > + struct folio_batch fbatch; > > + struct page *page = NULL; > > + struct folio *folio; > > + long ret; > > + > > + if (!nr_pages) > > + return -EINVAL; > > + > > + if (!memfd) > > + return -EINVAL; > > + > > + if (!shmem_file(memfd) && !is_file_hugepages(memfd)) > > + return -EINVAL; > > + > > + flags = memalloc_pin_save(); > > + do { > > + folio_batch_init(&fbatch); > > + start_idx = start; > > + i = 0; > > + > > + while (start_idx <= end_idx) { > > + /* > > + * In most cases, we should be able to find the page > > + * in the page cache. If we cannot find it for some > > + * reason, we try to allocate one and add it to the > > + * page cache. > > + */ > > + nr_folios = filemap_get_folios_contig(memfd- > >f_mapping, > > + &start_idx, > > + end_idx, > > + &fbatch); > > + if (page) { > > + put_page(page); > > + page = NULL; > > + } > > + for (j = 0; j < nr_folios; j++) { > > + folio = fbatch.folios[j]; > > + ret = try_grab_page(&folio->page, FOLL_PIN); > > + if (unlikely(ret)) { > > + folio_batch_release(&fbatch); > > + goto err; > > + } > > + > > + pages[i++] = &folio->page; > > + } > > I might be wrong, but that interface is still inconsistent. I think your > intention is to always return folios (head pages), but why are we > returning pages from this interface then? > > It would be more consistent regarding the other GUP interfaces to return > the actual tail pages that fit the given "pgoff_t start". So if you > punch in "nr_pages" you expect to get "nr_pages" pages, and not some > other number of folios. > > Otherwise, this interface is highly confusing. > > If you always want to return folios, then better name it > "memfd_pin_user_folios" (or just "memfd_pin_folios") and pass in a range > (instead of a nr_pages parameter), and somehow indicate to the caller > how many folio were in that range, and if that range was fully covered. I think it makes sense to return folios from this interface; and considering my use-case, I'd like have this API return an error if it cannot pin (or allocate) the exact number of folios the caller requested. > > Or am I missing something? I can make the udmabuf driver use folios instead of pages too but the function check_and_migrate_movable_pages() in GUP still takes a list of pages. Do you think it is ok to use a local variable to collect all the head pages for this? Thanks, Vivek > > -- > Cheers, > > David / dhildenb >
On 07.12.23 06:09, Kasireddy, Vivek wrote: > Hi David, > >> On 05.12.23 06:35, Vivek Kasireddy wrote: >>> For drivers that would like to longterm-pin the pages associated >>> with a memfd, the pin_user_pages_fd() API provides an option to >>> not only pin the pages via FOLL_PIN but also to check and migrate >>> them if they reside in movable zone or CMA block. This API >>> currently works with memfds but it should work with any files >>> that belong to either shmemfs or hugetlbfs. Files belonging to >>> other filesystems are rejected for now. >>> >>> The pages need to be located first before pinning them via FOLL_PIN. >>> If they are found in the page cache, they can be immediately pinned. >>> Otherwise, they need to be allocated using the filesystem specific >>> APIs and then pinned. >>> >>> v2: >>> - Drop gup_flags and improve comments and commit message (David) >>> - Allocate a page if we cannot find in page cache for the hugetlbfs >>> case as well (David) >>> - Don't unpin pages if there is a migration related failure (David) >>> - Drop the unnecessary nr_pages <= 0 check (Jason) >>> - Have the caller of the API pass in file * instead of fd (Jason) >>> >>> v3: (David) >>> - Enclose the huge page allocation code with #ifdef >> CONFIG_HUGETLB_PAGE >>> (Build error reported by kernel test robot <lkp@intel.com>) >>> - Don't forget memalloc_pin_restore() on non-migration related errors >>> - Improve the readability of the cleanup code associated with >>> non-migration related errors >>> - Augment the comments by describing FOLL_LONGTERM like behavior >>> - Include the R-b tag from Jason >>> >>> v4: >>> - Remove the local variable "page" and instead use 3 return statements >>> in alloc_file_page() (David) >>> - Add the R-b tag from David >>> >>> v5: (David) >>> - For hugetlb case, ensure that we only obtain head pages from the >>> mapping by using __filemap_get_folio() instead of find_get_page_flags() >>> - Handle -EEXIST when two or more potential users try to simultaneously >>> add a huge page to the mapping by forcing them to retry on failure >>> >>> v6: (Christoph) >>> - Rename this API to memfd_pin_user_pages() to make it clear that it >>> is intended for memfds >>> - Move the memfd page allocation helper from gup.c to memfd.c >>> - Fix indentation errors in memfd_pin_user_pages() >>> - For contiguous ranges of folios, use a helper such as >>> filemap_get_folios_contig() to lookup the page cache in batches >>> >>> Cc: David Hildenbrand <david@redhat.com> >>> Cc: Christoph Hellwig <hch@infradead.org> >>> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> >>> Cc: Mike Kravetz <mike.kravetz@oracle.com> >>> Cc: Hugh Dickins <hughd@google.com> >>> Cc: Peter Xu <peterx@redhat.com> >>> Cc: Gerd Hoffmann <kraxel@redhat.com> >>> Cc: Dongwon Kim <dongwon.kim@intel.com> >>> Cc: Junxiao Chang <junxiao.chang@intel.com> >>> Suggested-by: Jason Gunthorpe <jgg@nvidia.com> >>> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> (v2) >>> Reviewed-by: David Hildenbrand <david@redhat.com> (v3) >>> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com> >>> --- >>> include/linux/memfd.h | 5 +++ >>> include/linux/mm.h | 2 + >>> mm/gup.c | 102 ++++++++++++++++++++++++++++++++++++++++++ >>> mm/memfd.c | 34 ++++++++++++++ >>> 4 files changed, 143 insertions(+) >>> >>> diff --git a/include/linux/memfd.h b/include/linux/memfd.h >>> index e7abf6fa4c52..6fc0d1282151 100644 >>> --- a/include/linux/memfd.h >>> +++ b/include/linux/memfd.h >>> @@ -6,11 +6,16 @@ >>> >>> #ifdef CONFIG_MEMFD_CREATE >>> extern long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int >> arg); >>> +extern struct page *memfd_alloc_page(struct file *memfd, pgoff_t idx); >>> #else >>> static inline long memfd_fcntl(struct file *f, unsigned int c, unsigned int a) >>> { >>> return -EINVAL; >>> } >>> +static inline struct page *memfd_alloc_page(struct file *memfd, pgoff_t >> idx) >>> +{ >>> + return ERR_PTR(-EINVAL); >>> +} >>> #endif >>> >>> #endif /* __LINUX_MEMFD_H */ >>> diff --git a/include/linux/mm.h b/include/linux/mm.h >>> index 418d26608ece..ac69db45509f 100644 >>> --- a/include/linux/mm.h >>> +++ b/include/linux/mm.h >>> @@ -2472,6 +2472,8 @@ long get_user_pages_unlocked(unsigned long >> start, unsigned long nr_pages, >>> struct page **pages, unsigned int gup_flags); >>> long pin_user_pages_unlocked(unsigned long start, unsigned long >> nr_pages, >>> struct page **pages, unsigned int gup_flags); >>> +long memfd_pin_user_pages(struct file *file, pgoff_t start, >>> + unsigned long nr_pages, struct page **pages); >>> >>> int get_user_pages_fast(unsigned long start, int nr_pages, >>> unsigned int gup_flags, struct page **pages); >>> diff --git a/mm/gup.c b/mm/gup.c >>> index 231711efa390..eb93d1ec9dc6 100644 >>> --- a/mm/gup.c >>> +++ b/mm/gup.c >>> @@ -5,6 +5,7 @@ >>> #include <linux/spinlock.h> >>> >>> #include <linux/mm.h> >>> +#include <linux/memfd.h> >>> #include <linux/memremap.h> >>> #include <linux/pagemap.h> >>> #include <linux/rmap.h> >>> @@ -17,6 +18,7 @@ >>> #include <linux/hugetlb.h> >>> #include <linux/migrate.h> >>> #include <linux/mm_inline.h> >>> +#include <linux/pagevec.h> >>> #include <linux/sched/mm.h> >>> #include <linux/shmem_fs.h> >>> >>> @@ -3410,3 +3412,103 @@ long pin_user_pages_unlocked(unsigned long >> start, unsigned long nr_pages, >>> &locked, gup_flags); >>> } >>> EXPORT_SYMBOL(pin_user_pages_unlocked); >>> + >>> +/** >>> + * memfd_pin_user_pages() - pin user pages associated with a memfd >>> + * @memfd: the memfd whose pages are to be pinned >>> + * @start: starting memfd offset >>> + * @nr_pages: number of pages from start to pin >>> + * @pages: array that receives pointers to the pages pinned. >>> + * Should be at-least nr_pages long. >>> + * >>> + * Attempt to pin pages associated with a memfd; given that a memfd is >> either >>> + * backed by shmem or hugetlb, the pages can either be found in the page >> cache >>> + * or need to be allocated if necessary. Once the pages are located, they >> are >>> + * all pinned via FOLL_PIN. And, these pinned pages need to be released >> either >>> + * using unpin_user_pages() or unpin_user_page(). >>> + * >>> + * It must be noted that the pages may be pinned for an indefinite amount >>> + * of time. And, in most cases, the duration of time they may stay pinned >>> + * would be controlled by the userspace. This behavior is effectively the >>> + * same as using FOLL_LONGTERM with other GUP APIs. >>> + * >>> + * Returns number of pages pinned. This would be equal to the number of >>> + * pages requested. If no pages were pinned, it returns -errno. >>> + */ >>> +long memfd_pin_user_pages(struct file *memfd, pgoff_t start, >>> + unsigned long nr_pages, struct page **pages) >>> +{ >>> + pgoff_t start_idx, end_idx = start + nr_pages - 1; >>> + unsigned int flags, nr_folios, i, j; >>> + struct folio_batch fbatch; >>> + struct page *page = NULL; >>> + struct folio *folio; >>> + long ret; >>> + >>> + if (!nr_pages) >>> + return -EINVAL; >>> + >>> + if (!memfd) >>> + return -EINVAL; >>> + >>> + if (!shmem_file(memfd) && !is_file_hugepages(memfd)) >>> + return -EINVAL; >>> + >>> + flags = memalloc_pin_save(); >>> + do { >>> + folio_batch_init(&fbatch); >>> + start_idx = start; >>> + i = 0; >>> + >>> + while (start_idx <= end_idx) { >>> + /* >>> + * In most cases, we should be able to find the page >>> + * in the page cache. If we cannot find it for some >>> + * reason, we try to allocate one and add it to the >>> + * page cache. >>> + */ >>> + nr_folios = filemap_get_folios_contig(memfd- >>> f_mapping, >>> + &start_idx, >>> + end_idx, >>> + &fbatch); >>> + if (page) { >>> + put_page(page); >>> + page = NULL; >>> + } >>> + for (j = 0; j < nr_folios; j++) { >>> + folio = fbatch.folios[j]; >>> + ret = try_grab_page(&folio->page, FOLL_PIN); >>> + if (unlikely(ret)) { >>> + folio_batch_release(&fbatch); >>> + goto err; >>> + } >>> + >>> + pages[i++] = &folio->page; >>> + } >> >> I might be wrong, but that interface is still inconsistent. I think your >> intention is to always return folios (head pages), but why are we >> returning pages from this interface then? >> >> It would be more consistent regarding the other GUP interfaces to return >> the actual tail pages that fit the given "pgoff_t start". So if you >> punch in "nr_pages" you expect to get "nr_pages" pages, and not some >> other number of folios. >> >> Otherwise, this interface is highly confusing. >> >> If you always want to return folios, then better name it >> "memfd_pin_user_folios" (or just "memfd_pin_folios") and pass in a range >> (instead of a nr_pages parameter), and somehow indicate to the caller >> how many folio were in that range, and if that range was fully covered. > I think it makes sense to return folios from this interface; and considering my > use-case, I'd like have this API return an error if it cannot pin (or allocate) > the exact number of folios the caller requested. Okay, then better use folios. Assuming a caller puts in "start = X" and gets some large folio back. How is the caller supposed to know at which offset to look into that folio (IOW< which subpage)? For "pages" it was obvious (you get the actual subpages), but as soon as we return a large folio, some information is missing for the caller. How can the caller figure that out? > >> >> Or am I missing something? > I can make the udmabuf driver use folios instead of pages too but the function > check_and_migrate_movable_pages() in GUP still takes a list of pages. Do you > think it is ok to use a local variable to collect all the head pages for this? I think you can simply pass in the head page, because only whole folios can be converted. At some point we should convert that one to use folios as well.
On Thu, Dec 07, 2023 at 10:44:14AM +0100, David Hildenbrand wrote: > > > If you always want to return folios, then better name it > > > "memfd_pin_user_folios" (or just "memfd_pin_folios") and pass in a range > > > (instead of a nr_pages parameter), and somehow indicate to the caller > > > how many folio were in that range, and if that range was fully covered. > > I think it makes sense to return folios from this interface; and considering my > > use-case, I'd like have this API return an error if it cannot pin (or allocate) > > the exact number of folios the caller requested. > > Okay, then better use folios. > > Assuming a caller puts in "start = X" and gets some large folio back. How is > the caller supposed to know at which offset to look into that folio (IOW< > which subpage)? For "pages" it was obvious (you get the actual subpages), > but as soon as we return a large folio, some information is missing for the > caller. > > How can the caller figure that out? This can only work if the memfd is required to only have full folios at aligned locations. Under that restriction computing the first folio offset is easy enough: folio offset = (start % folio size) But is that true for the memfds here? > > I can make the udmabuf driver use folios instead of pages too but the function > > check_and_migrate_movable_pages() in GUP still takes a list of pages. Do you > > think it is ok to use a local variable to collect all the head pages for this? > > I think you can simply pass in the head page, because only whole folios can > be converted. At some point we should convert that one to use folios as > well. It is like that because it processes the output from GUP in-place which is a page list.. Probably what we need to do is make the migration checks happen while accumulating the pages so we don't need to scan the output list.. Jason
On 07.12.23 14:05, Jason Gunthorpe wrote: > On Thu, Dec 07, 2023 at 10:44:14AM +0100, David Hildenbrand wrote: > >>>> If you always want to return folios, then better name it >>>> "memfd_pin_user_folios" (or just "memfd_pin_folios") and pass in a range >>>> (instead of a nr_pages parameter), and somehow indicate to the caller >>>> how many folio were in that range, and if that range was fully covered. >>> I think it makes sense to return folios from this interface; and considering my >>> use-case, I'd like have this API return an error if it cannot pin (or allocate) >>> the exact number of folios the caller requested. >> >> Okay, then better use folios. >> >> Assuming a caller puts in "start = X" and gets some large folio back. How is >> the caller supposed to know at which offset to look into that folio (IOW< >> which subpage)? For "pages" it was obvious (you get the actual subpages), >> but as soon as we return a large folio, some information is missing for the >> caller. >> >> How can the caller figure that out? > > This can only work if the memfd is required to only have full folios > at aligned locations. Under that restriction computing the first folio > offset is easy enough: > > folio offset = (start % folio size) > > But is that true for the memfds here? I assume folios are always naturally aligned, like: [ 2m ][ 2m ][1m][1m][ 2m ] ^f0 ^f1 ^f2 ^f3 ^f4 If you query the range "3m -> 7m", you get back f1,f2,f3,f4 and have to start in the middle of the first folio with offset 1m. From there, it is indeed simply continuing with the full folio size -- until the last folio, where you want to only process 1m. folio offset = (1m % 2m) would be correct in that case.
Hi David, > > > >> On 05.12.23 06:35, Vivek Kasireddy wrote: > >>> For drivers that would like to longterm-pin the pages associated > >>> with a memfd, the pin_user_pages_fd() API provides an option to > >>> not only pin the pages via FOLL_PIN but also to check and migrate > >>> them if they reside in movable zone or CMA block. This API > >>> currently works with memfds but it should work with any files > >>> that belong to either shmemfs or hugetlbfs. Files belonging to > >>> other filesystems are rejected for now. > >>> > >>> The pages need to be located first before pinning them via FOLL_PIN. > >>> If they are found in the page cache, they can be immediately pinned. > >>> Otherwise, they need to be allocated using the filesystem specific > >>> APIs and then pinned. > >>> > >>> v2: > >>> - Drop gup_flags and improve comments and commit message (David) > >>> - Allocate a page if we cannot find in page cache for the hugetlbfs > >>> case as well (David) > >>> - Don't unpin pages if there is a migration related failure (David) > >>> - Drop the unnecessary nr_pages <= 0 check (Jason) > >>> - Have the caller of the API pass in file * instead of fd (Jason) > >>> > >>> v3: (David) > >>> - Enclose the huge page allocation code with #ifdef > >> CONFIG_HUGETLB_PAGE > >>> (Build error reported by kernel test robot <lkp@intel.com>) > >>> - Don't forget memalloc_pin_restore() on non-migration related errors > >>> - Improve the readability of the cleanup code associated with > >>> non-migration related errors > >>> - Augment the comments by describing FOLL_LONGTERM like behavior > >>> - Include the R-b tag from Jason > >>> > >>> v4: > >>> - Remove the local variable "page" and instead use 3 return statements > >>> in alloc_file_page() (David) > >>> - Add the R-b tag from David > >>> > >>> v5: (David) > >>> - For hugetlb case, ensure that we only obtain head pages from the > >>> mapping by using __filemap_get_folio() instead of > find_get_page_flags() > >>> - Handle -EEXIST when two or more potential users try to simultaneously > >>> add a huge page to the mapping by forcing them to retry on failure > >>> > >>> v6: (Christoph) > >>> - Rename this API to memfd_pin_user_pages() to make it clear that it > >>> is intended for memfds > >>> - Move the memfd page allocation helper from gup.c to memfd.c > >>> - Fix indentation errors in memfd_pin_user_pages() > >>> - For contiguous ranges of folios, use a helper such as > >>> filemap_get_folios_contig() to lookup the page cache in batches > >>> > >>> Cc: David Hildenbrand <david@redhat.com> > >>> Cc: Christoph Hellwig <hch@infradead.org> > >>> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> > >>> Cc: Mike Kravetz <mike.kravetz@oracle.com> > >>> Cc: Hugh Dickins <hughd@google.com> > >>> Cc: Peter Xu <peterx@redhat.com> > >>> Cc: Gerd Hoffmann <kraxel@redhat.com> > >>> Cc: Dongwon Kim <dongwon.kim@intel.com> > >>> Cc: Junxiao Chang <junxiao.chang@intel.com> > >>> Suggested-by: Jason Gunthorpe <jgg@nvidia.com> > >>> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> (v2) > >>> Reviewed-by: David Hildenbrand <david@redhat.com> (v3) > >>> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com> > >>> --- > >>> include/linux/memfd.h | 5 +++ > >>> include/linux/mm.h | 2 + > >>> mm/gup.c | 102 > ++++++++++++++++++++++++++++++++++++++++++ > >>> mm/memfd.c | 34 ++++++++++++++ > >>> 4 files changed, 143 insertions(+) > >>> > >>> diff --git a/include/linux/memfd.h b/include/linux/memfd.h > >>> index e7abf6fa4c52..6fc0d1282151 100644 > >>> --- a/include/linux/memfd.h > >>> +++ b/include/linux/memfd.h > >>> @@ -6,11 +6,16 @@ > >>> > >>> #ifdef CONFIG_MEMFD_CREATE > >>> extern long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int > >> arg); > >>> +extern struct page *memfd_alloc_page(struct file *memfd, pgoff_t idx); > >>> #else > >>> static inline long memfd_fcntl(struct file *f, unsigned int c, unsigned int > a) > >>> { > >>> return -EINVAL; > >>> } > >>> +static inline struct page *memfd_alloc_page(struct file *memfd, pgoff_t > >> idx) > >>> +{ > >>> + return ERR_PTR(-EINVAL); > >>> +} > >>> #endif > >>> > >>> #endif /* __LINUX_MEMFD_H */ > >>> diff --git a/include/linux/mm.h b/include/linux/mm.h > >>> index 418d26608ece..ac69db45509f 100644 > >>> --- a/include/linux/mm.h > >>> +++ b/include/linux/mm.h > >>> @@ -2472,6 +2472,8 @@ long get_user_pages_unlocked(unsigned long > >> start, unsigned long nr_pages, > >>> struct page **pages, unsigned int gup_flags); > >>> long pin_user_pages_unlocked(unsigned long start, unsigned long > >> nr_pages, > >>> struct page **pages, unsigned int gup_flags); > >>> +long memfd_pin_user_pages(struct file *file, pgoff_t start, > >>> + unsigned long nr_pages, struct page **pages); > >>> > >>> int get_user_pages_fast(unsigned long start, int nr_pages, > >>> unsigned int gup_flags, struct page **pages); > >>> diff --git a/mm/gup.c b/mm/gup.c > >>> index 231711efa390..eb93d1ec9dc6 100644 > >>> --- a/mm/gup.c > >>> +++ b/mm/gup.c > >>> @@ -5,6 +5,7 @@ > >>> #include <linux/spinlock.h> > >>> > >>> #include <linux/mm.h> > >>> +#include <linux/memfd.h> > >>> #include <linux/memremap.h> > >>> #include <linux/pagemap.h> > >>> #include <linux/rmap.h> > >>> @@ -17,6 +18,7 @@ > >>> #include <linux/hugetlb.h> > >>> #include <linux/migrate.h> > >>> #include <linux/mm_inline.h> > >>> +#include <linux/pagevec.h> > >>> #include <linux/sched/mm.h> > >>> #include <linux/shmem_fs.h> > >>> > >>> @@ -3410,3 +3412,103 @@ long pin_user_pages_unlocked(unsigned > long > >> start, unsigned long nr_pages, > >>> &locked, gup_flags); > >>> } > >>> EXPORT_SYMBOL(pin_user_pages_unlocked); > >>> + > >>> +/** > >>> + * memfd_pin_user_pages() - pin user pages associated with a memfd > >>> + * @memfd: the memfd whose pages are to be pinned > >>> + * @start: starting memfd offset > >>> + * @nr_pages: number of pages from start to pin > >>> + * @pages: array that receives pointers to the pages pinned. > >>> + * Should be at-least nr_pages long. > >>> + * > >>> + * Attempt to pin pages associated with a memfd; given that a memfd is > >> either > >>> + * backed by shmem or hugetlb, the pages can either be found in the > page > >> cache > >>> + * or need to be allocated if necessary. Once the pages are located, they > >> are > >>> + * all pinned via FOLL_PIN. And, these pinned pages need to be released > >> either > >>> + * using unpin_user_pages() or unpin_user_page(). > >>> + * > >>> + * It must be noted that the pages may be pinned for an indefinite > amount > >>> + * of time. And, in most cases, the duration of time they may stay > pinned > >>> + * would be controlled by the userspace. This behavior is effectively the > >>> + * same as using FOLL_LONGTERM with other GUP APIs. > >>> + * > >>> + * Returns number of pages pinned. This would be equal to the number > of > >>> + * pages requested. If no pages were pinned, it returns -errno. > >>> + */ > >>> +long memfd_pin_user_pages(struct file *memfd, pgoff_t start, > >>> + unsigned long nr_pages, struct page **pages) > >>> +{ > >>> + pgoff_t start_idx, end_idx = start + nr_pages - 1; > >>> + unsigned int flags, nr_folios, i, j; > >>> + struct folio_batch fbatch; > >>> + struct page *page = NULL; > >>> + struct folio *folio; > >>> + long ret; > >>> + > >>> + if (!nr_pages) > >>> + return -EINVAL; > >>> + > >>> + if (!memfd) > >>> + return -EINVAL; > >>> + > >>> + if (!shmem_file(memfd) && !is_file_hugepages(memfd)) > >>> + return -EINVAL; > >>> + > >>> + flags = memalloc_pin_save(); > >>> + do { > >>> + folio_batch_init(&fbatch); > >>> + start_idx = start; > >>> + i = 0; > >>> + > >>> + while (start_idx <= end_idx) { > >>> + /* > >>> + * In most cases, we should be able to find the page > >>> + * in the page cache. If we cannot find it for some > >>> + * reason, we try to allocate one and add it to the > >>> + * page cache. > >>> + */ > >>> + nr_folios = filemap_get_folios_contig(memfd- > >>> f_mapping, > >>> + &start_idx, > >>> + end_idx, > >>> + &fbatch); > >>> + if (page) { > >>> + put_page(page); > >>> + page = NULL; > >>> + } > >>> + for (j = 0; j < nr_folios; j++) { > >>> + folio = fbatch.folios[j]; > >>> + ret = try_grab_page(&folio->page, FOLL_PIN); > >>> + if (unlikely(ret)) { > >>> + folio_batch_release(&fbatch); > >>> + goto err; > >>> + } > >>> + > >>> + pages[i++] = &folio->page; > >>> + } > >> > >> I might be wrong, but that interface is still inconsistent. I think your > >> intention is to always return folios (head pages), but why are we > >> returning pages from this interface then? > >> > >> It would be more consistent regarding the other GUP interfaces to return > >> the actual tail pages that fit the given "pgoff_t start". So if you > >> punch in "nr_pages" you expect to get "nr_pages" pages, and not some > >> other number of folios. > >> > >> Otherwise, this interface is highly confusing. > >> > >> If you always want to return folios, then better name it > >> "memfd_pin_user_folios" (or just "memfd_pin_folios") and pass in a > range > >> (instead of a nr_pages parameter), and somehow indicate to the caller > >> how many folio were in that range, and if that range was fully covered. > > I think it makes sense to return folios from this interface; and considering > my > > use-case, I'd like have this API return an error if it cannot pin (or allocate) > > the exact number of folios the caller requested. > > Okay, then better use folios. > > Assuming a caller puts in "start = X" and gets some large folio back. > How is the caller supposed to know at which offset to look into that > folio (IOW< which subpage)? For "pages" it was obvious (you get the > actual subpages), but as soon as we return a large folio, some > information is missing for the caller. > > How can the caller figure that out? I think the caller can deduce the subpage offset one way or the other. For example, in udmabuf we do: subpgoff = offset & ~huge_page_mask(hpstate); Do you think it is reasonable to expect callers to make these deductions? Or would it make more sense to have the caller pass in an empty array that this API would eventually fill with offsets? Thanks, Vivek > > > > >> > >> Or am I missing something? > > I can make the udmabuf driver use folios instead of pages too but the > function > > check_and_migrate_movable_pages() in GUP still takes a list of pages. Do > you > > think it is ok to use a local variable to collect all the head pages for this? > > I think you can simply pass in the head page, because only whole folios > can be converted. At some point we should convert that one to use folios > as well. > > -- > Cheers, > > David / dhildenb
On 08.12.23 08:57, Kasireddy, Vivek wrote: > Hi David, > >>> >>>> On 05.12.23 06:35, Vivek Kasireddy wrote: >>>>> For drivers that would like to longterm-pin the pages associated >>>>> with a memfd, the pin_user_pages_fd() API provides an option to >>>>> not only pin the pages via FOLL_PIN but also to check and migrate >>>>> them if they reside in movable zone or CMA block. This API >>>>> currently works with memfds but it should work with any files >>>>> that belong to either shmemfs or hugetlbfs. Files belonging to >>>>> other filesystems are rejected for now. >>>>> >>>>> The pages need to be located first before pinning them via FOLL_PIN. >>>>> If they are found in the page cache, they can be immediately pinned. >>>>> Otherwise, they need to be allocated using the filesystem specific >>>>> APIs and then pinned. >>>>> >>>>> v2: >>>>> - Drop gup_flags and improve comments and commit message (David) >>>>> - Allocate a page if we cannot find in page cache for the hugetlbfs >>>>> case as well (David) >>>>> - Don't unpin pages if there is a migration related failure (David) >>>>> - Drop the unnecessary nr_pages <= 0 check (Jason) >>>>> - Have the caller of the API pass in file * instead of fd (Jason) >>>>> >>>>> v3: (David) >>>>> - Enclose the huge page allocation code with #ifdef >>>> CONFIG_HUGETLB_PAGE >>>>> (Build error reported by kernel test robot <lkp@intel.com>) >>>>> - Don't forget memalloc_pin_restore() on non-migration related errors >>>>> - Improve the readability of the cleanup code associated with >>>>> non-migration related errors >>>>> - Augment the comments by describing FOLL_LONGTERM like behavior >>>>> - Include the R-b tag from Jason >>>>> >>>>> v4: >>>>> - Remove the local variable "page" and instead use 3 return statements >>>>> in alloc_file_page() (David) >>>>> - Add the R-b tag from David >>>>> >>>>> v5: (David) >>>>> - For hugetlb case, ensure that we only obtain head pages from the >>>>> mapping by using __filemap_get_folio() instead of >> find_get_page_flags() >>>>> - Handle -EEXIST when two or more potential users try to simultaneously >>>>> add a huge page to the mapping by forcing them to retry on failure >>>>> >>>>> v6: (Christoph) >>>>> - Rename this API to memfd_pin_user_pages() to make it clear that it >>>>> is intended for memfds >>>>> - Move the memfd page allocation helper from gup.c to memfd.c >>>>> - Fix indentation errors in memfd_pin_user_pages() >>>>> - For contiguous ranges of folios, use a helper such as >>>>> filemap_get_folios_contig() to lookup the page cache in batches >>>>> >>>>> Cc: David Hildenbrand <david@redhat.com> >>>>> Cc: Christoph Hellwig <hch@infradead.org> >>>>> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> >>>>> Cc: Mike Kravetz <mike.kravetz@oracle.com> >>>>> Cc: Hugh Dickins <hughd@google.com> >>>>> Cc: Peter Xu <peterx@redhat.com> >>>>> Cc: Gerd Hoffmann <kraxel@redhat.com> >>>>> Cc: Dongwon Kim <dongwon.kim@intel.com> >>>>> Cc: Junxiao Chang <junxiao.chang@intel.com> >>>>> Suggested-by: Jason Gunthorpe <jgg@nvidia.com> >>>>> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> (v2) >>>>> Reviewed-by: David Hildenbrand <david@redhat.com> (v3) >>>>> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com> >>>>> --- >>>>> include/linux/memfd.h | 5 +++ >>>>> include/linux/mm.h | 2 + >>>>> mm/gup.c | 102 >> ++++++++++++++++++++++++++++++++++++++++++ >>>>> mm/memfd.c | 34 ++++++++++++++ >>>>> 4 files changed, 143 insertions(+) >>>>> >>>>> diff --git a/include/linux/memfd.h b/include/linux/memfd.h >>>>> index e7abf6fa4c52..6fc0d1282151 100644 >>>>> --- a/include/linux/memfd.h >>>>> +++ b/include/linux/memfd.h >>>>> @@ -6,11 +6,16 @@ >>>>> >>>>> #ifdef CONFIG_MEMFD_CREATE >>>>> extern long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int >>>> arg); >>>>> +extern struct page *memfd_alloc_page(struct file *memfd, pgoff_t idx); >>>>> #else >>>>> static inline long memfd_fcntl(struct file *f, unsigned int c, unsigned int >> a) >>>>> { >>>>> return -EINVAL; >>>>> } >>>>> +static inline struct page *memfd_alloc_page(struct file *memfd, pgoff_t >>>> idx) >>>>> +{ >>>>> + return ERR_PTR(-EINVAL); >>>>> +} >>>>> #endif >>>>> >>>>> #endif /* __LINUX_MEMFD_H */ >>>>> diff --git a/include/linux/mm.h b/include/linux/mm.h >>>>> index 418d26608ece..ac69db45509f 100644 >>>>> --- a/include/linux/mm.h >>>>> +++ b/include/linux/mm.h >>>>> @@ -2472,6 +2472,8 @@ long get_user_pages_unlocked(unsigned long >>>> start, unsigned long nr_pages, >>>>> struct page **pages, unsigned int gup_flags); >>>>> long pin_user_pages_unlocked(unsigned long start, unsigned long >>>> nr_pages, >>>>> struct page **pages, unsigned int gup_flags); >>>>> +long memfd_pin_user_pages(struct file *file, pgoff_t start, >>>>> + unsigned long nr_pages, struct page **pages); >>>>> >>>>> int get_user_pages_fast(unsigned long start, int nr_pages, >>>>> unsigned int gup_flags, struct page **pages); >>>>> diff --git a/mm/gup.c b/mm/gup.c >>>>> index 231711efa390..eb93d1ec9dc6 100644 >>>>> --- a/mm/gup.c >>>>> +++ b/mm/gup.c >>>>> @@ -5,6 +5,7 @@ >>>>> #include <linux/spinlock.h> >>>>> >>>>> #include <linux/mm.h> >>>>> +#include <linux/memfd.h> >>>>> #include <linux/memremap.h> >>>>> #include <linux/pagemap.h> >>>>> #include <linux/rmap.h> >>>>> @@ -17,6 +18,7 @@ >>>>> #include <linux/hugetlb.h> >>>>> #include <linux/migrate.h> >>>>> #include <linux/mm_inline.h> >>>>> +#include <linux/pagevec.h> >>>>> #include <linux/sched/mm.h> >>>>> #include <linux/shmem_fs.h> >>>>> >>>>> @@ -3410,3 +3412,103 @@ long pin_user_pages_unlocked(unsigned >> long >>>> start, unsigned long nr_pages, >>>>> &locked, gup_flags); >>>>> } >>>>> EXPORT_SYMBOL(pin_user_pages_unlocked); >>>>> + >>>>> +/** >>>>> + * memfd_pin_user_pages() - pin user pages associated with a memfd >>>>> + * @memfd: the memfd whose pages are to be pinned >>>>> + * @start: starting memfd offset >>>>> + * @nr_pages: number of pages from start to pin >>>>> + * @pages: array that receives pointers to the pages pinned. >>>>> + * Should be at-least nr_pages long. >>>>> + * >>>>> + * Attempt to pin pages associated with a memfd; given that a memfd is >>>> either >>>>> + * backed by shmem or hugetlb, the pages can either be found in the >> page >>>> cache >>>>> + * or need to be allocated if necessary. Once the pages are located, they >>>> are >>>>> + * all pinned via FOLL_PIN. And, these pinned pages need to be released >>>> either >>>>> + * using unpin_user_pages() or unpin_user_page(). >>>>> + * >>>>> + * It must be noted that the pages may be pinned for an indefinite >> amount >>>>> + * of time. And, in most cases, the duration of time they may stay >> pinned >>>>> + * would be controlled by the userspace. This behavior is effectively the >>>>> + * same as using FOLL_LONGTERM with other GUP APIs. >>>>> + * >>>>> + * Returns number of pages pinned. This would be equal to the number >> of >>>>> + * pages requested. If no pages were pinned, it returns -errno. >>>>> + */ >>>>> +long memfd_pin_user_pages(struct file *memfd, pgoff_t start, >>>>> + unsigned long nr_pages, struct page **pages) >>>>> +{ >>>>> + pgoff_t start_idx, end_idx = start + nr_pages - 1; >>>>> + unsigned int flags, nr_folios, i, j; >>>>> + struct folio_batch fbatch; >>>>> + struct page *page = NULL; >>>>> + struct folio *folio; >>>>> + long ret; >>>>> + >>>>> + if (!nr_pages) >>>>> + return -EINVAL; >>>>> + >>>>> + if (!memfd) >>>>> + return -EINVAL; >>>>> + >>>>> + if (!shmem_file(memfd) && !is_file_hugepages(memfd)) >>>>> + return -EINVAL; >>>>> + >>>>> + flags = memalloc_pin_save(); >>>>> + do { >>>>> + folio_batch_init(&fbatch); >>>>> + start_idx = start; >>>>> + i = 0; >>>>> + >>>>> + while (start_idx <= end_idx) { >>>>> + /* >>>>> + * In most cases, we should be able to find the page >>>>> + * in the page cache. If we cannot find it for some >>>>> + * reason, we try to allocate one and add it to the >>>>> + * page cache. >>>>> + */ >>>>> + nr_folios = filemap_get_folios_contig(memfd- >>>>> f_mapping, >>>>> + &start_idx, >>>>> + end_idx, >>>>> + &fbatch); >>>>> + if (page) { >>>>> + put_page(page); >>>>> + page = NULL; >>>>> + } >>>>> + for (j = 0; j < nr_folios; j++) { >>>>> + folio = fbatch.folios[j]; >>>>> + ret = try_grab_page(&folio->page, FOLL_PIN); >>>>> + if (unlikely(ret)) { >>>>> + folio_batch_release(&fbatch); >>>>> + goto err; >>>>> + } >>>>> + >>>>> + pages[i++] = &folio->page; >>>>> + } >>>> >>>> I might be wrong, but that interface is still inconsistent. I think your >>>> intention is to always return folios (head pages), but why are we >>>> returning pages from this interface then? >>>> >>>> It would be more consistent regarding the other GUP interfaces to return >>>> the actual tail pages that fit the given "pgoff_t start". So if you >>>> punch in "nr_pages" you expect to get "nr_pages" pages, and not some >>>> other number of folios. >>>> >>>> Otherwise, this interface is highly confusing. >>>> >>>> If you always want to return folios, then better name it >>>> "memfd_pin_user_folios" (or just "memfd_pin_folios") and pass in a >> range >>>> (instead of a nr_pages parameter), and somehow indicate to the caller >>>> how many folio were in that range, and if that range was fully covered. >>> I think it makes sense to return folios from this interface; and considering >> my >>> use-case, I'd like have this API return an error if it cannot pin (or allocate) >>> the exact number of folios the caller requested. >> >> Okay, then better use folios. >> >> Assuming a caller puts in "start = X" and gets some large folio back. >> How is the caller supposed to know at which offset to look into that >> folio (IOW< which subpage)? For "pages" it was obvious (you get the >> actual subpages), but as soon as we return a large folio, some >> information is missing for the caller. >> >> How can the caller figure that out? > I think the caller can deduce the subpage offset one way or the other. For > example, in udmabuf we do: > subpgoff = offset & ~huge_page_mask(hpstate); For hugetlb it's obvious, because we always have fixed-sized chunks for the whole memfd. > Do you think it is reasonable to expect callers to make these deductions? > Or would it make more sense to have the caller pass in an empty array > that this API would eventually fill with offsets? Only the offset into the first folio is really required. From there, it's mostly just processing full folios (well, the last folio might have to be processed partially, but that's easy to figure out by the caller by keeping track of the total range processed vs. requested). Maybe it makes sense to return the offset into the first folio? Would certainly take some magic out of that interface.
diff --git a/include/linux/memfd.h b/include/linux/memfd.h index e7abf6fa4c52..6fc0d1282151 100644 --- a/include/linux/memfd.h +++ b/include/linux/memfd.h @@ -6,11 +6,16 @@ #ifdef CONFIG_MEMFD_CREATE extern long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int arg); +extern struct page *memfd_alloc_page(struct file *memfd, pgoff_t idx); #else static inline long memfd_fcntl(struct file *f, unsigned int c, unsigned int a) { return -EINVAL; } +static inline struct page *memfd_alloc_page(struct file *memfd, pgoff_t idx) +{ + return ERR_PTR(-EINVAL); +} #endif #endif /* __LINUX_MEMFD_H */ diff --git a/include/linux/mm.h b/include/linux/mm.h index 418d26608ece..ac69db45509f 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2472,6 +2472,8 @@ long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages, struct page **pages, unsigned int gup_flags); long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages, struct page **pages, unsigned int gup_flags); +long memfd_pin_user_pages(struct file *file, pgoff_t start, + unsigned long nr_pages, struct page **pages); int get_user_pages_fast(unsigned long start, int nr_pages, unsigned int gup_flags, struct page **pages); diff --git a/mm/gup.c b/mm/gup.c index 231711efa390..eb93d1ec9dc6 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -5,6 +5,7 @@ #include <linux/spinlock.h> #include <linux/mm.h> +#include <linux/memfd.h> #include <linux/memremap.h> #include <linux/pagemap.h> #include <linux/rmap.h> @@ -17,6 +18,7 @@ #include <linux/hugetlb.h> #include <linux/migrate.h> #include <linux/mm_inline.h> +#include <linux/pagevec.h> #include <linux/sched/mm.h> #include <linux/shmem_fs.h> @@ -3410,3 +3412,103 @@ long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages, &locked, gup_flags); } EXPORT_SYMBOL(pin_user_pages_unlocked); + +/** + * memfd_pin_user_pages() - pin user pages associated with a memfd + * @memfd: the memfd whose pages are to be pinned + * @start: starting memfd offset + * @nr_pages: number of pages from start to pin + * @pages: array that receives pointers to the pages pinned. + * Should be at-least nr_pages long. + * + * Attempt to pin pages associated with a memfd; given that a memfd is either + * backed by shmem or hugetlb, the pages can either be found in the page cache + * or need to be allocated if necessary. Once the pages are located, they are + * all pinned via FOLL_PIN. And, these pinned pages need to be released either + * using unpin_user_pages() or unpin_user_page(). + * + * It must be noted that the pages may be pinned for an indefinite amount + * of time. And, in most cases, the duration of time they may stay pinned + * would be controlled by the userspace. This behavior is effectively the + * same as using FOLL_LONGTERM with other GUP APIs. + * + * Returns number of pages pinned. This would be equal to the number of + * pages requested. If no pages were pinned, it returns -errno. + */ +long memfd_pin_user_pages(struct file *memfd, pgoff_t start, + unsigned long nr_pages, struct page **pages) +{ + pgoff_t start_idx, end_idx = start + nr_pages - 1; + unsigned int flags, nr_folios, i, j; + struct folio_batch fbatch; + struct page *page = NULL; + struct folio *folio; + long ret; + + if (!nr_pages) + return -EINVAL; + + if (!memfd) + return -EINVAL; + + if (!shmem_file(memfd) && !is_file_hugepages(memfd)) + return -EINVAL; + + flags = memalloc_pin_save(); + do { + folio_batch_init(&fbatch); + start_idx = start; + i = 0; + + while (start_idx <= end_idx) { + /* + * In most cases, we should be able to find the page + * in the page cache. If we cannot find it for some + * reason, we try to allocate one and add it to the + * page cache. + */ + nr_folios = filemap_get_folios_contig(memfd->f_mapping, + &start_idx, + end_idx, + &fbatch); + if (page) { + put_page(page); + page = NULL; + } + for (j = 0; j < nr_folios; j++) { + folio = fbatch.folios[j]; + ret = try_grab_page(&folio->page, FOLL_PIN); + if (unlikely(ret)) { + folio_batch_release(&fbatch); + goto err; + } + + pages[i++] = &folio->page; + } + + folio_batch_release(&fbatch); + if (!nr_folios) { + page = memfd_alloc_page(memfd, start_idx); + if (IS_ERR(page)) { + ret = PTR_ERR(page); + if (ret != -EEXIST) + goto err; + } + } + } + + ret = check_and_migrate_movable_pages(nr_pages, pages); + } while (ret == -EAGAIN); + + memalloc_pin_restore(flags); + return ret ? ret : nr_pages; +err: + memalloc_pin_restore(flags); + while (i-- > 0) + if (pages[i]) + unpin_user_page(pages[i]); + + return ret; +} +EXPORT_SYMBOL_GPL(memfd_pin_user_pages); + diff --git a/mm/memfd.c b/mm/memfd.c index d3a1ba4208c9..b315cd12bdb7 100644 --- a/mm/memfd.c +++ b/mm/memfd.c @@ -63,6 +63,40 @@ static void memfd_tag_pins(struct xa_state *xas) xas_unlock_irq(xas); } +/* + * This is a helper function used by memfd_pin_user_pages() in GUP (gup.c). + * It is mainly called to allocate a page in a memfd when the caller + * (memfd_pin_user_pages()) cannot find a page in the page cache at a given + * index in the mapping. + */ +struct page *memfd_alloc_page(struct file *memfd, pgoff_t idx) +{ +#ifdef CONFIG_HUGETLB_PAGE + struct folio *folio; + int err; + + if (is_file_hugepages(memfd)) { + folio = alloc_hugetlb_folio_nodemask(hstate_file(memfd), + NUMA_NO_NODE, + NULL, + GFP_USER); + if (folio && folio_try_get(folio)) { + err = hugetlb_add_to_page_cache(folio, + memfd->f_mapping, + idx); + if (err) { + folio_put(folio); + free_huge_folio(folio); + return ERR_PTR(err); + } + return &folio->page; + } + return ERR_PTR(-ENOMEM); + } +#endif + return shmem_read_mapping_page(memfd->f_mapping, idx); +} + /* * Setting SEAL_WRITE requires us to verify there's no pending writer. However, * via get_user_pages(), drivers might have some pending I/O without any active