| Message ID | 3f6d04570907ee80f030ffaa85e8f506b3d31fc1.1659680600.git-series.apopple@nvidia.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2,1/2] mm/gup.c: Don't pass gup_flags to check_and_migrate_movable_pages() | expand |
On 05.08.22 08:29, Alistair Popple wrote: > When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() > is called to migrate pages out of zones which should not contain any > longterm pinned pages. > > When migration succeeds all pages will have been unpinned so pinning > needs to be retried. Migration can also fail, in which case the pages > will also have been unpinned but the operation should not be retried. If > all pages are in the correct zone nothing will be unpinned and no retry > is required. > > The logic in check_and_migrate_movable_pages() tracks unnecessary state > and the return codes for each case are difficult to follow. Refactor the > code to clean this up. No behaviour change is intended. > > Signed-off-by: Alistair Popple <apopple@nvidia.com> > > --- > > Changes for v2: > > - Split into different functions as suggested by John. > - Made error handling more conventional as requested by Jason. > > Personally I'm not entirely convinced the conventional approach to error > handling is easier to follow here but have left it in for feedback as I > might be getting too familiar with the code. > > Originally posted as "mm/gup.c: Simplify and fix > check_and_migrate_movable_pages() return codes"[1]. > > Changes from that version: > > - Restore the original isolation failure behaviour and don't fail the > pup. Instead retry indefinitely. > - Unpin all pages on retry or failure rather than just failure. > > [1] https://lore.kernel.org/linux-mm/814dee5d3aadd38c3370eaaf438ba7eee9bf9d2b.1659399696.git-series.apopple@nvidia.com/ > --- > mm/gup.c | 159 ++++++++++++++++++++++++++++++-------------------------- > 1 file changed, 88 insertions(+), 71 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index e26ccc0..60cb30a 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -1900,20 +1900,14 @@ struct page *get_dump_page(unsigned long addr) > #endif /* CONFIG_ELF_CORE */ > > #ifdef CONFIG_MIGRATION > -/* > - * Check whether all pages are pinnable, if so return number of pages. If some > - * pages are not pinnable, migrate them, and unpin all pages. Return zero if > - * pages were migrated, or if some pages were not successfully isolated. > - * Return negative error if migration fails. > - */ > -static long check_and_migrate_movable_pages(unsigned long nr_pages, > - struct page **pages) > +static int collect_unpinnable_pages(struct list_head *movable_page_list, If we're already renaming stuff, can we make it clearer, that we are dealing with *longterm* unpinnable pages?
On 8/4/22 23:29, Alistair Popple wrote: > When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() > is called to migrate pages out of zones which should not contain any > longterm pinned pages. > > When migration succeeds all pages will have been unpinned so pinning > needs to be retried. Migration can also fail, in which case the pages > will also have been unpinned but the operation should not be retried. If > all pages are in the correct zone nothing will be unpinned and no retry > is required. > > The logic in check_and_migrate_movable_pages() tracks unnecessary state > and the return codes for each case are difficult to follow. Refactor the > code to clean this up. No behaviour change is intended. > > Signed-off-by: Alistair Popple <apopple@nvidia.com> > > --- > > Changes for v2: > > - Split into different functions as suggested by John. > - Made error handling more conventional as requested by Jason. > > Personally I'm not entirely convinced the conventional approach to error > handling is easier to follow here but have left it in for feedback as I > might be getting too familiar with the code. > > Originally posted as "mm/gup.c: Simplify and fix > check_and_migrate_movable_pages() return codes"[1]. > > Changes from that version: > > - Restore the original isolation failure behaviour and don't fail the > pup. Instead retry indefinitely. > - Unpin all pages on retry or failure rather than just failure. > > [1] https://lore.kernel.org/linux-mm/814dee5d3aadd38c3370eaaf438ba7eee9bf9d2b.1659399696.git-series.apopple@nvidia.com/ > --- > mm/gup.c | 159 ++++++++++++++++++++++++++++++-------------------------- > 1 file changed, 88 insertions(+), 71 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index e26ccc0..60cb30a 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -1900,20 +1900,14 @@ struct page *get_dump_page(unsigned long addr) > #endif /* CONFIG_ELF_CORE */ > > #ifdef CONFIG_MIGRATION > -/* > - * Check whether all pages are pinnable, if so return number of pages. If some > - * pages are not pinnable, migrate them, and unpin all pages. Return zero if > - * pages were migrated, or if some pages were not successfully isolated. > - * Return negative error if migration fails. > - */ > -static long check_and_migrate_movable_pages(unsigned long nr_pages, > - struct page **pages) Let's add: /* * Returns the number of collected pages. Return value is always >= 0. */ > +static int collect_unpinnable_pages(struct list_head *movable_page_list, > + unsigned long nr_pages, > + struct page **pages) > { > - unsigned long isolation_error_count = 0, i; > + unsigned long i; > + int collected = 0; This should be an unsigned long. > struct folio *prev_folio = NULL; > - LIST_HEAD(movable_page_list); > - bool drain_allow = true, coherent_pages = false; > - int ret = 0; > + bool drain_allow = true; > > for (i = 0; i < nr_pages; i++) { > struct folio *folio = page_folio(pages[i]); > @@ -1922,43 +1916,16 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages, > continue; > prev_folio = folio; > > - /* > - * Device coherent pages are managed by a driver and should not > - * be pinned indefinitely as it prevents the driver moving the > - * page. So when trying to pin with FOLL_LONGTERM instead try > - * to migrate the page out of device memory. > - */ > - if (folio_is_device_coherent(folio)) { > - /* > - * We always want a new GUP lookup with device coherent > - * pages. > - */ > - pages[i] = 0; > - coherent_pages = true; > - > - /* > - * Migration will fail if the page is pinned, so convert > - * the pin on the source page to a normal reference. > - */ > - get_page(&folio->page); > - unpin_user_page(&folio->page); > + if (folio_is_longterm_pinnable(folio)) > + continue; > > - ret = migrate_device_coherent_page(&folio->page); > - if (ret) > - goto unpin_pages; > + collected++; > > + if (folio_is_device_coherent(folio)) > continue; > - } > > - if (folio_is_longterm_pinnable(folio)) > - continue; > - /* > - * Try to move out any movable page before pinning the range. > - */ > if (folio_test_hugetlb(folio)) { > - if (isolate_hugetlb(&folio->page, > - &movable_page_list)) > - isolation_error_count++; > + isolate_hugetlb(&folio->page, movable_page_list); > continue; > } > > @@ -1967,59 +1934,109 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages, > drain_allow = false; > } > > - if (folio_isolate_lru(folio)) { > - isolation_error_count++; > + if (!folio_isolate_lru(folio)) > continue; > - } > - list_add_tail(&folio->lru, &movable_page_list); > + > + list_add_tail(&folio->lru, movable_page_list); > node_stat_mod_folio(folio, > NR_ISOLATED_ANON + folio_is_file_lru(folio), > folio_nr_pages(folio)); > } > > - if (!list_empty(&movable_page_list) || isolation_error_count || > - coherent_pages) > - goto unpin_pages; > + return collected; > +} > > - /* > - * If list is empty, and no isolation errors, means that all pages are > - * in the correct zone. > - */ > - return nr_pages; Let's add approximately (maybe there is better wording): /* * Returns zero for success, or -errno for failure (or partial success). */ > +static int migrate_unpinnable_pages(struct list_head *movable_page_list, > + unsigned long nr_pages, > + struct page **pages) > +{ > + int ret, i; There is an uneasy mixing of int and long and unsigned long. Instead, this should use unsigned long whenever it deals with nr_pages. Like here. > > -unpin_pages: > - /* > - * pages[i] might be NULL if any device coherent pages were found. > - */ > for (i = 0; i < nr_pages; i++) { > - if (!pages[i]) > + struct folio *folio = page_folio(pages[i]); > + > + if (folio_is_device_coherent(folio)) { > + /* > + * Migration will fail if the page is pinned, so convert > + * the pin on the source page to a normal reference. > + */ > + pages[i] = NULL; > + get_page(&folio->page); > + unpin_user_page(&folio->page); > + > + if (migrate_device_coherent_page(&folio->page)) { > + ret = -EBUSY; > + goto err; > + } > + > continue; > + } > > + /* > + * We can't migrate pages with unexpected references, so drop > + * the reference obtained by get_user_pages(). The get_user_pages() reference is confusing, since we only handle FOLL_PIN here. It's hard to connect the comment to the code. Maybe a more precise pointer to where the reference was taken would help. > + * folio_isolate_lru() takes a reference so the page won't be > + * freed. Also confusing because it's difficult to connect the comment back to the code. Maybe mention where folio_isolate_lru() is called from in this case? > + */ > unpin_user_page(pages[i]); > + pages[i] = NULL; Is this correct? The loop covers all of nr_pages, so we are setting every pages[i] = NULL, for non-DEV_COHERENT cases. This seems wrong. > } > > - if (!list_empty(&movable_page_list)) { > + if (!list_empty(movable_page_list)) { > struct migration_target_control mtc = { > .nid = NUMA_NO_NODE, > .gfp_mask = GFP_USER | __GFP_NOWARN, > }; > > - ret = migrate_pages(&movable_page_list, alloc_migration_target, > - NULL, (unsigned long)&mtc, MIGRATE_SYNC, > - MR_LONGTERM_PIN, NULL); > - if (ret > 0) /* number of pages not migrated */ > + if (migrate_pages(movable_page_list, alloc_migration_target, > + NULL, (unsigned long)&mtc, MIGRATE_SYNC, > + MR_LONGTERM_PIN, NULL)) { > ret = -ENOMEM; > + goto err; > + } > } > > - if (ret && !list_empty(&movable_page_list)) > - putback_movable_pages(&movable_page_list); > + putback_movable_pages(movable_page_list); > + > + return 0; > + > +err: > + for (i = 0; i < nr_pages; i++) > + if (pages[i]) > + unpin_user_page(pages[i]); > + putback_movable_pages(movable_page_list); > + > return ret; > } > + > +/* > + * Check whether all pages are pinnable. If some pages are not pinnable migrate > + * them and unpin all the pages. Returns -EAGAIN if pages were unpinned or zero > + * if all pages are pinnable and in the right zone. Other errors indicate > + * migration failure. > + */ > +static long check_and_migrate_movable_pages(unsigned long nr_pages, > + struct page **pages) > +{ > + int ret; > + long collected; That should be unsigned long, too. > + LIST_HEAD(movable_page_list); > + > + collected = collect_unpinnable_pages(&movable_page_list, nr_pages, pages); > + if (!collected) > + return 0; > + > + ret = migrate_unpinnable_pages(&movable_page_list, nr_pages, pages); > + if (!ret) > + return -EAGAIN; > + else > + return ret; > +} > #else > static long check_and_migrate_movable_pages(unsigned long nr_pages, > struct page **pages) > { > - return nr_pages; > + return 0; > } > #endif /* CONFIG_MIGRATION */ > > @@ -2049,10 +2066,10 @@ static long __gup_longterm_locked(struct mm_struct *mm, > > WARN_ON_ONCE(!(gup_flags & FOLL_PIN)); > rc = check_and_migrate_movable_pages(rc, pages); > - } while (!rc); > + } while (rc == -EAGAIN); > memalloc_pin_restore(flags); > > - return rc; > + return rc ? rc : nr_pages; This seems to add some holes in the handling of error cases. If -EBUSY or -ENOMEM happens, then we return an -errno, rather than the number of pinned pages. But some pages may have been pinned. Previously it just looped if there was any error, so that couldn't happen. thanks,
John Hubbard <jhubbard@nvidia.com> writes: Thanks John, have fixed most of this but a couple of comments below. > On 8/4/22 23:29, Alistair Popple wrote: [...] >> + /* >> + * We can't migrate pages with unexpected references, so drop >> + * the reference obtained by get_user_pages(). > > The get_user_pages() reference is confusing, since we only handle FOLL_PIN > here. It's hard to connect the comment to the code. Maybe a more precise > pointer to where the reference was taken would help. Ok. Is changing the reference to __get_user_pages_locked() better? (I get that this is the FOLL_PIN case, but that is the function that actually does that in __gup_longterm_locked()). >> + * folio_isolate_lru() takes a reference so the page won't be >> + * freed. > > Also confusing because it's difficult to connect the comment back to the code. > Maybe mention where folio_isolate_lru() is called from in this case? Will update this to: /* * We can't migrate pages with unexpected references, so drop * the reference obtained by __get_user_pages_locked(). * Migrating pages have been added to movable_page_list after * calling folio_isolate_lru() which takes a reference so the * page won't be freed if it's migrating. */ I'd rather not explicitly call out the function where folio_isolate_lru() is called as that could change. However it should be pretty easy to find where pages are added to movable_page_list and pages should never be on that list without being isolated anyway so this better documents what the code assumes IMHO. >> + */ >> unpin_user_page(pages[i]); >> + pages[i] = NULL; > > Is this correct? The loop covers all of nr_pages, so we are setting every > pages[i] = NULL, for non-DEV_COHERENT cases. This seems wrong. Yes, this is correct. Regardless of error or success we have to unpin the pages, and if we've unpinned the pages we need to clear them from the pages[] array. Will update the function description to include this. This is also partly why I wasn't convinced the 'goto err' error handling was better - we need to take the same actions regardless of error or not and that perhaps makes it less clear. [...] >> @@ -2049,10 +2066,10 @@ static long __gup_longterm_locked(struct mm_struct >> *mm, >> WARN_ON_ONCE(!(gup_flags & FOLL_PIN)); >> rc = check_and_migrate_movable_pages(rc, pages); >> - } while (!rc); >> + } while (rc == -EAGAIN); >> memalloc_pin_restore(flags); >> - return rc; >> + return rc ? rc : nr_pages; > > This seems to add some holes in the handling of error cases. If -EBUSY > or -ENOMEM happens, then we return an -errno, rather than the number > of pinned pages. But some pages may have been pinned. No they won't - as mentioned above migrate_unpinnable_pages() will (or at least should) always clear and unpin all pages. - Alistair > Previously it just looped if there was any error, so that couldn't > happen. > > > thanks,
diff --git a/mm/gup.c b/mm/gup.c index e26ccc0..60cb30a 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1900,20 +1900,14 @@ struct page *get_dump_page(unsigned long addr) #endif /* CONFIG_ELF_CORE */ #ifdef CONFIG_MIGRATION -/* - * Check whether all pages are pinnable, if so return number of pages. If some - * pages are not pinnable, migrate them, and unpin all pages. Return zero if - * pages were migrated, or if some pages were not successfully isolated. - * Return negative error if migration fails. - */ -static long check_and_migrate_movable_pages(unsigned long nr_pages, - struct page **pages) +static int collect_unpinnable_pages(struct list_head *movable_page_list, + unsigned long nr_pages, + struct page **pages) { - unsigned long isolation_error_count = 0, i; + unsigned long i; + int collected = 0; struct folio *prev_folio = NULL; - LIST_HEAD(movable_page_list); - bool drain_allow = true, coherent_pages = false; - int ret = 0; + bool drain_allow = true; for (i = 0; i < nr_pages; i++) { struct folio *folio = page_folio(pages[i]); @@ -1922,43 +1916,16 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages, continue; prev_folio = folio; - /* - * Device coherent pages are managed by a driver and should not - * be pinned indefinitely as it prevents the driver moving the - * page. So when trying to pin with FOLL_LONGTERM instead try - * to migrate the page out of device memory. - */ - if (folio_is_device_coherent(folio)) { - /* - * We always want a new GUP lookup with device coherent - * pages. - */ - pages[i] = 0; - coherent_pages = true; - - /* - * Migration will fail if the page is pinned, so convert - * the pin on the source page to a normal reference. - */ - get_page(&folio->page); - unpin_user_page(&folio->page); + if (folio_is_longterm_pinnable(folio)) + continue; - ret = migrate_device_coherent_page(&folio->page); - if (ret) - goto unpin_pages; + collected++; + if (folio_is_device_coherent(folio)) continue; - } - if (folio_is_longterm_pinnable(folio)) - continue; - /* - * Try to move out any movable page before pinning the range. - */ if (folio_test_hugetlb(folio)) { - if (isolate_hugetlb(&folio->page, - &movable_page_list)) - isolation_error_count++; + isolate_hugetlb(&folio->page, movable_page_list); continue; } @@ -1967,59 +1934,109 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages, drain_allow = false; } - if (folio_isolate_lru(folio)) { - isolation_error_count++; + if (!folio_isolate_lru(folio)) continue; - } - list_add_tail(&folio->lru, &movable_page_list); + + list_add_tail(&folio->lru, movable_page_list); node_stat_mod_folio(folio, NR_ISOLATED_ANON + folio_is_file_lru(folio), folio_nr_pages(folio)); } - if (!list_empty(&movable_page_list) || isolation_error_count || - coherent_pages) - goto unpin_pages; + return collected; +} - /* - * If list is empty, and no isolation errors, means that all pages are - * in the correct zone. - */ - return nr_pages; +static int migrate_unpinnable_pages(struct list_head *movable_page_list, + unsigned long nr_pages, + struct page **pages) +{ + int ret, i; -unpin_pages: - /* - * pages[i] might be NULL if any device coherent pages were found. - */ for (i = 0; i < nr_pages; i++) { - if (!pages[i]) + struct folio *folio = page_folio(pages[i]); + + if (folio_is_device_coherent(folio)) { + /* + * Migration will fail if the page is pinned, so convert + * the pin on the source page to a normal reference. + */ + pages[i] = NULL; + get_page(&folio->page); + unpin_user_page(&folio->page); + + if (migrate_device_coherent_page(&folio->page)) { + ret = -EBUSY; + goto err; + } + continue; + } + /* + * We can't migrate pages with unexpected references, so drop + * the reference obtained by get_user_pages(). + * folio_isolate_lru() takes a reference so the page won't be + * freed. + */ unpin_user_page(pages[i]); + pages[i] = NULL; } - if (!list_empty(&movable_page_list)) { + if (!list_empty(movable_page_list)) { struct migration_target_control mtc = { .nid = NUMA_NO_NODE, .gfp_mask = GFP_USER | __GFP_NOWARN, }; - ret = migrate_pages(&movable_page_list, alloc_migration_target, - NULL, (unsigned long)&mtc, MIGRATE_SYNC, - MR_LONGTERM_PIN, NULL); - if (ret > 0) /* number of pages not migrated */ + if (migrate_pages(movable_page_list, alloc_migration_target, + NULL, (unsigned long)&mtc, MIGRATE_SYNC, + MR_LONGTERM_PIN, NULL)) { ret = -ENOMEM; + goto err; + } } - if (ret && !list_empty(&movable_page_list)) - putback_movable_pages(&movable_page_list); + putback_movable_pages(movable_page_list); + + return 0; + +err: + for (i = 0; i < nr_pages; i++) + if (pages[i]) + unpin_user_page(pages[i]); + putback_movable_pages(movable_page_list); + return ret; } + +/* + * Check whether all pages are pinnable. If some pages are not pinnable migrate + * them and unpin all the pages. Returns -EAGAIN if pages were unpinned or zero + * if all pages are pinnable and in the right zone. Other errors indicate + * migration failure. + */ +static long check_and_migrate_movable_pages(unsigned long nr_pages, + struct page **pages) +{ + int ret; + long collected; + LIST_HEAD(movable_page_list); + + collected = collect_unpinnable_pages(&movable_page_list, nr_pages, pages); + if (!collected) + return 0; + + ret = migrate_unpinnable_pages(&movable_page_list, nr_pages, pages); + if (!ret) + return -EAGAIN; + else + return ret; +} #else static long check_and_migrate_movable_pages(unsigned long nr_pages, struct page **pages) { - return nr_pages; + return 0; } #endif /* CONFIG_MIGRATION */ @@ -2049,10 +2066,10 @@ static long __gup_longterm_locked(struct mm_struct *mm, WARN_ON_ONCE(!(gup_flags & FOLL_PIN)); rc = check_and_migrate_movable_pages(rc, pages); - } while (!rc); + } while (rc == -EAGAIN); memalloc_pin_restore(flags); - return rc; + return rc ? rc : nr_pages; } static bool is_valid_gup_flags(unsigned int gup_flags)
When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() is called to migrate pages out of zones which should not contain any longterm pinned pages. When migration succeeds all pages will have been unpinned so pinning needs to be retried. Migration can also fail, in which case the pages will also have been unpinned but the operation should not be retried. If all pages are in the correct zone nothing will be unpinned and no retry is required. The logic in check_and_migrate_movable_pages() tracks unnecessary state and the return codes for each case are difficult to follow. Refactor the code to clean this up. No behaviour change is intended. Signed-off-by: Alistair Popple <apopple@nvidia.com> --- Changes for v2: - Split into different functions as suggested by John. - Made error handling more conventional as requested by Jason. Personally I'm not entirely convinced the conventional approach to error handling is easier to follow here but have left it in for feedback as I might be getting too familiar with the code. Originally posted as "mm/gup.c: Simplify and fix check_and_migrate_movable_pages() return codes"[1]. Changes from that version: - Restore the original isolation failure behaviour and don't fail the pup. Instead retry indefinitely. - Unpin all pages on retry or failure rather than just failure. [1] https://lore.kernel.org/linux-mm/814dee5d3aadd38c3370eaaf438ba7eee9bf9d2b.1659399696.git-series.apopple@nvidia.com/ --- mm/gup.c | 159 ++++++++++++++++++++++++++++++-------------------------- 1 file changed, 88 insertions(+), 71 deletions(-)