| Message ID | 20200925204442.31348-2-rcampbell@nvidia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm: remove extra ZONE_DEVICE struct page refcount | expand |
On Fri, Sep 25, 2020 at 1:45 PM Ralph Campbell <rcampbell@nvidia.com> wrote: > > There are several places where ZONE_DEVICE struct pages assume a reference > count == 1 means the page is idle and free. Instead of open coding this, > add a helper function to hide this detail. > > Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> > --- > fs/dax.c | 8 ++++---- > fs/ext4/inode.c | 2 +- > fs/xfs/xfs_file.c | 2 +- > include/linux/dax.h | 5 +++++ > 4 files changed, 11 insertions(+), 6 deletions(-) > > diff --git a/fs/dax.c b/fs/dax.c > index 994ab66a9907..8eddbcc0e149 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -358,7 +358,7 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping, > for_each_mapped_pfn(entry, pfn) { > struct page *page = pfn_to_page(pfn); > > - WARN_ON_ONCE(trunc && page_ref_count(page) > 1); > + WARN_ON_ONCE(trunc && !dax_layout_is_idle_page(page)); > WARN_ON_ONCE(page->mapping && page->mapping != mapping); > page->mapping = NULL; > page->index = 0; > @@ -372,7 +372,7 @@ static struct page *dax_busy_page(void *entry) > for_each_mapped_pfn(entry, pfn) { > struct page *page = pfn_to_page(pfn); > > - if (page_ref_count(page) > 1) > + if (!dax_layout_is_idle_page(page)) > return page; > } > return NULL; > @@ -560,11 +560,11 @@ static void *grab_mapping_entry(struct xa_state *xas, > > /** > * dax_layout_busy_page - find first pinned page in @mapping > - * @mapping: address space to scan for a page with ref count > 1 > + * @mapping: address space to scan for a page with ref count > 0 > * > * DAX requires ZONE_DEVICE mapped pages. These pages are never > * 'onlined' to the page allocator so they are considered idle when > - * page->count == 1. A filesystem uses this interface to determine if > + * page->count == 0. A filesystem uses this interface to determine if > * any page in the mapping is busy, i.e. for DMA, or other > * get_user_pages() usages. > * > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > index bf596467c234..d9f8ad55523a 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -3927,7 +3927,7 @@ int ext4_break_layouts(struct inode *inode) > return 0; > > error = ___wait_var_event(&page->_refcount, > - atomic_read(&page->_refcount) == 1, > + dax_layout_is_idle_page(page), > TASK_INTERRUPTIBLE, 0, 0, > ext4_wait_dax_page(ei)); > } while (error == 0); > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c > index a29f78a663ca..29ab96541bc1 100644 > --- a/fs/xfs/xfs_file.c > +++ b/fs/xfs/xfs_file.c > @@ -750,7 +750,7 @@ xfs_break_dax_layouts( > > *retry = true; > return ___wait_var_event(&page->_refcount, > - atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE, > + dax_layout_is_idle_page(page), TASK_INTERRUPTIBLE, > 0, 0, xfs_wait_dax_page(inode)); > } > > diff --git a/include/linux/dax.h b/include/linux/dax.h > index 43b39ab9de1a..3f78ed78d1d6 100644 > --- a/include/linux/dax.h > +++ b/include/linux/dax.h > @@ -238,4 +238,9 @@ static inline bool dax_mapping(struct address_space *mapping) > return mapping->host && IS_DAX(mapping->host); > } > > +static inline bool dax_layout_is_idle_page(struct page *page) > +{ > + return page_ref_count(page) <= 1; Why convert the check from "== 1" to "<= 1" and then back to the == operator in the next patch? A refcount < 1 in this path before your other change is a bug.
On 9/25/20 1:51 PM, Dan Williams wrote: > On Fri, Sep 25, 2020 at 1:45 PM Ralph Campbell <rcampbell@nvidia.com> wrote: >> >> There are several places where ZONE_DEVICE struct pages assume a reference >> count == 1 means the page is idle and free. Instead of open coding this, >> add a helper function to hide this detail. >> >> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> >> --- >> fs/dax.c | 8 ++++---- >> fs/ext4/inode.c | 2 +- >> fs/xfs/xfs_file.c | 2 +- >> include/linux/dax.h | 5 +++++ >> 4 files changed, 11 insertions(+), 6 deletions(-) >> >> diff --git a/fs/dax.c b/fs/dax.c >> index 994ab66a9907..8eddbcc0e149 100644 >> --- a/fs/dax.c >> +++ b/fs/dax.c >> @@ -358,7 +358,7 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping, >> for_each_mapped_pfn(entry, pfn) { >> struct page *page = pfn_to_page(pfn); >> >> - WARN_ON_ONCE(trunc && page_ref_count(page) > 1); >> + WARN_ON_ONCE(trunc && !dax_layout_is_idle_page(page)); >> WARN_ON_ONCE(page->mapping && page->mapping != mapping); >> page->mapping = NULL; >> page->index = 0; >> @@ -372,7 +372,7 @@ static struct page *dax_busy_page(void *entry) >> for_each_mapped_pfn(entry, pfn) { >> struct page *page = pfn_to_page(pfn); >> >> - if (page_ref_count(page) > 1) >> + if (!dax_layout_is_idle_page(page)) >> return page; >> } >> return NULL; >> @@ -560,11 +560,11 @@ static void *grab_mapping_entry(struct xa_state *xas, >> >> /** >> * dax_layout_busy_page - find first pinned page in @mapping >> - * @mapping: address space to scan for a page with ref count > 1 >> + * @mapping: address space to scan for a page with ref count > 0 >> * >> * DAX requires ZONE_DEVICE mapped pages. These pages are never >> * 'onlined' to the page allocator so they are considered idle when >> - * page->count == 1. A filesystem uses this interface to determine if >> + * page->count == 0. A filesystem uses this interface to determine if >> * any page in the mapping is busy, i.e. for DMA, or other >> * get_user_pages() usages. >> * >> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c >> index bf596467c234..d9f8ad55523a 100644 >> --- a/fs/ext4/inode.c >> +++ b/fs/ext4/inode.c >> @@ -3927,7 +3927,7 @@ int ext4_break_layouts(struct inode *inode) >> return 0; >> >> error = ___wait_var_event(&page->_refcount, >> - atomic_read(&page->_refcount) == 1, >> + dax_layout_is_idle_page(page), >> TASK_INTERRUPTIBLE, 0, 0, >> ext4_wait_dax_page(ei)); >> } while (error == 0); >> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c >> index a29f78a663ca..29ab96541bc1 100644 >> --- a/fs/xfs/xfs_file.c >> +++ b/fs/xfs/xfs_file.c >> @@ -750,7 +750,7 @@ xfs_break_dax_layouts( >> >> *retry = true; >> return ___wait_var_event(&page->_refcount, >> - atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE, >> + dax_layout_is_idle_page(page), TASK_INTERRUPTIBLE, >> 0, 0, xfs_wait_dax_page(inode)); >> } >> >> diff --git a/include/linux/dax.h b/include/linux/dax.h >> index 43b39ab9de1a..3f78ed78d1d6 100644 >> --- a/include/linux/dax.h >> +++ b/include/linux/dax.h >> @@ -238,4 +238,9 @@ static inline bool dax_mapping(struct address_space *mapping) >> return mapping->host && IS_DAX(mapping->host); >> } >> >> +static inline bool dax_layout_is_idle_page(struct page *page) >> +{ >> + return page_ref_count(page) <= 1; > > Why convert the check from "== 1" to "<= 1" and then back to the == > operator in the next patch? A refcount < 1 in this path before your > other change is a bug. > Mostly I was thinking > 1 was busy so <= 1 is idle. And yes, <=0 is never supposed to happen. Checking for == 1 is probably better though.
On Fri, Sep 25, 2020 at 01:44:41PM -0700, Ralph Campbell wrote: > error = ___wait_var_event(&page->_refcount, > - atomic_read(&page->_refcount) == 1, > + dax_layout_is_idle_page(page), > TASK_INTERRUPTIBLE, 0, 0, > ext4_wait_dax_page(ei)); > +++ b/fs/xfs/xfs_file.c > @@ -750,7 +750,7 @@ xfs_break_dax_layouts( > > *retry = true; > return ___wait_var_event(&page->_refcount, > - atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE, > + dax_layout_is_idle_page(page), TASK_INTERRUPTIBLE, > 0, 0, xfs_wait_dax_page(inode)); > } I still think a litte helper macro would be nice here: #define dax_wait_page(_inode, _page, _wait_cb) \ ___wait_var_event(&(_page)->_refcount, \ atomic_read(&(_page)->_refcount) == 1, \ TASK_INTERRUPTIBLE, dax_layout_is_idle_page(_page), \ TASK_INTERRUPTIBLE, 0, 0, _wait_cb(_inode));
On 9/25/20 11:35 PM, Christoph Hellwig wrote: > On Fri, Sep 25, 2020 at 01:44:41PM -0700, Ralph Campbell wrote: >> error = ___wait_var_event(&page->_refcount, >> - atomic_read(&page->_refcount) == 1, >> + dax_layout_is_idle_page(page), >> TASK_INTERRUPTIBLE, 0, 0, >> ext4_wait_dax_page(ei)); > >> +++ b/fs/xfs/xfs_file.c >> @@ -750,7 +750,7 @@ xfs_break_dax_layouts( >> >> *retry = true; >> return ___wait_var_event(&page->_refcount, >> - atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE, >> + dax_layout_is_idle_page(page), TASK_INTERRUPTIBLE, >> 0, 0, xfs_wait_dax_page(inode)); >> } > > I still think a litte helper macro would be nice here: > > #define dax_wait_page(_inode, _page, _wait_cb) \ > ___wait_var_event(&(_page)->_refcount, \ > atomic_read(&(_page)->_refcount) == 1, \ > TASK_INTERRUPTIBLE, dax_layout_is_idle_page(_page), \ > TASK_INTERRUPTIBLE, 0, 0, _wait_cb(_inode)); OK, I'll add it in v3.
diff --git a/fs/dax.c b/fs/dax.c index 994ab66a9907..8eddbcc0e149 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -358,7 +358,7 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping, for_each_mapped_pfn(entry, pfn) { struct page *page = pfn_to_page(pfn); - WARN_ON_ONCE(trunc && page_ref_count(page) > 1); + WARN_ON_ONCE(trunc && !dax_layout_is_idle_page(page)); WARN_ON_ONCE(page->mapping && page->mapping != mapping); page->mapping = NULL; page->index = 0; @@ -372,7 +372,7 @@ static struct page *dax_busy_page(void *entry) for_each_mapped_pfn(entry, pfn) { struct page *page = pfn_to_page(pfn); - if (page_ref_count(page) > 1) + if (!dax_layout_is_idle_page(page)) return page; } return NULL; @@ -560,11 +560,11 @@ static void *grab_mapping_entry(struct xa_state *xas, /** * dax_layout_busy_page - find first pinned page in @mapping - * @mapping: address space to scan for a page with ref count > 1 + * @mapping: address space to scan for a page with ref count > 0 * * DAX requires ZONE_DEVICE mapped pages. These pages are never * 'onlined' to the page allocator so they are considered idle when - * page->count == 1. A filesystem uses this interface to determine if + * page->count == 0. A filesystem uses this interface to determine if * any page in the mapping is busy, i.e. for DMA, or other * get_user_pages() usages. * diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index bf596467c234..d9f8ad55523a 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -3927,7 +3927,7 @@ int ext4_break_layouts(struct inode *inode) return 0; error = ___wait_var_event(&page->_refcount, - atomic_read(&page->_refcount) == 1, + dax_layout_is_idle_page(page), TASK_INTERRUPTIBLE, 0, 0, ext4_wait_dax_page(ei)); } while (error == 0); diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index a29f78a663ca..29ab96541bc1 100644 --- a/fs/xfs/xfs_file.c +++ b/fs/xfs/xfs_file.c @@ -750,7 +750,7 @@ xfs_break_dax_layouts( *retry = true; return ___wait_var_event(&page->_refcount, - atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE, + dax_layout_is_idle_page(page), TASK_INTERRUPTIBLE, 0, 0, xfs_wait_dax_page(inode)); } diff --git a/include/linux/dax.h b/include/linux/dax.h index 43b39ab9de1a..3f78ed78d1d6 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -238,4 +238,9 @@ static inline bool dax_mapping(struct address_space *mapping) return mapping->host && IS_DAX(mapping->host); } +static inline bool dax_layout_is_idle_page(struct page *page) +{ + return page_ref_count(page) <= 1; +} + #endif
There are several places where ZONE_DEVICE struct pages assume a reference count == 1 means the page is idle and free. Instead of open coding this, add a helper function to hide this detail. Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> --- fs/dax.c | 8 ++++---- fs/ext4/inode.c | 2 +- fs/xfs/xfs_file.c | 2 +- include/linux/dax.h | 5 +++++ 4 files changed, 11 insertions(+), 6 deletions(-)