| Message ID | 879d62a8-91cc-d3c6-fb3b-69768236df68@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [mmotm] mm: __isolate_lru_page_prepare() in isolate_migratepages_block() | expand |
On Fri, 4 Mar 2022, Hugh Dickins wrote: > __isolate_lru_page_prepare() conflates two unrelated functions, with > the flags to one disjoint from the flags to the other; and hides some > of the important checks outside of isolate_migratepages_block(), where > the sequence is better to be visible. It comes from the days of lumpy > reclaim, before compaction, when the combination made more sense. > > Move what's needed by mm/compaction.c isolate_migratepages_block() inline > there, and what's needed by mm/vmscan.c isolate_lru_pages() inline there. > > Shorten "isolate_mode" to "mode", so the sequence of conditions is easier > to read. Declare a "mapping" variable, to save one call to page_mapping() > (but not another: calling again after page is locked is necessary). > Simplify isolate_lru_pages() with a "move_to" list pointer. > > Signed-off-by: Hugh Dickins <hughd@google.com> Acked-by: David Rientjes <rientjes@google.com>
On Sat, Mar 5, 2022 at 1:01 PM Hugh Dickins <hughd@google.com> wrote: > > __isolate_lru_page_prepare() conflates two unrelated functions, with > the flags to one disjoint from the flags to the other; and hides some > of the important checks outside of isolate_migratepages_block(), where > the sequence is better to be visible. It comes from the days of lumpy > reclaim, before compaction, when the combination made more sense. > > Move what's needed by mm/compaction.c isolate_migratepages_block() inline > there, and what's needed by mm/vmscan.c isolate_lru_pages() inline there. > > Shorten "isolate_mode" to "mode", so the sequence of conditions is easier > to read. Declare a "mapping" variable, to save one call to page_mapping() > (but not another: calling again after page is locked is necessary). > Simplify isolate_lru_pages() with a "move_to" list pointer. > > Signed-off-by: Hugh Dickins <hughd@google.com> Reviewed-by: Alex Shi <alexs@kernel.org> > --- > > include/linux/swap.h | 1 - > mm/compaction.c | 51 ++++++++++++++++++++++---- > mm/vmscan.c | 101 +++++++++------------------------------------------ > 3 files changed, 62 insertions(+), 91 deletions(-) > > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -386,7 +386,6 @@ extern void lru_cache_add_inactive_or_unevictable(struct page *page, > extern unsigned long zone_reclaimable_pages(struct zone *zone); > extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order, > gfp_t gfp_mask, nodemask_t *mask); > -extern bool __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode); > extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, > unsigned long nr_pages, > gfp_t gfp_mask, > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -785,7 +785,7 @@ static bool too_many_isolated(pg_data_t *pgdat) > * @cc: Compaction control structure. > * @low_pfn: The first PFN to isolate > * @end_pfn: The one-past-the-last PFN to isolate, within same pageblock > - * @isolate_mode: Isolation mode to be used. > + * @mode: Isolation mode to be used. > * > * Isolate all pages that can be migrated from the range specified by > * [low_pfn, end_pfn). The range is expected to be within same pageblock. > @@ -798,7 +798,7 @@ static bool too_many_isolated(pg_data_t *pgdat) > */ > static int > isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > - unsigned long end_pfn, isolate_mode_t isolate_mode) > + unsigned long end_pfn, isolate_mode_t mode) > { > pg_data_t *pgdat = cc->zone->zone_pgdat; > unsigned long nr_scanned = 0, nr_isolated = 0; > @@ -806,6 +806,7 @@ static bool too_many_isolated(pg_data_t *pgdat) > unsigned long flags = 0; > struct lruvec *locked = NULL; > struct page *page = NULL, *valid_page = NULL; > + struct address_space *mapping; > unsigned long start_pfn = low_pfn; > bool skip_on_failure = false; > unsigned long next_skip_pfn = 0; > @@ -990,7 +991,7 @@ static bool too_many_isolated(pg_data_t *pgdat) > locked = NULL; > } > > - if (!isolate_movable_page(page, isolate_mode)) > + if (!isolate_movable_page(page, mode)) > goto isolate_success; > } > > @@ -1002,15 +1003,15 @@ static bool too_many_isolated(pg_data_t *pgdat) > * so avoid taking lru_lock and isolating it unnecessarily in an > * admittedly racy check. > */ > - if (!page_mapping(page) && > - page_count(page) > page_mapcount(page)) > + mapping = page_mapping(page); > + if (!mapping && page_count(page) > page_mapcount(page)) > goto isolate_fail; > > /* > * Only allow to migrate anonymous pages in GFP_NOFS context > * because those do not depend on fs locks. > */ > - if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page)) > + if (!(cc->gfp_mask & __GFP_FS) && mapping) > goto isolate_fail; > > /* > @@ -1021,9 +1022,45 @@ static bool too_many_isolated(pg_data_t *pgdat) > if (unlikely(!get_page_unless_zero(page))) > goto isolate_fail; > > - if (!__isolate_lru_page_prepare(page, isolate_mode)) > + /* Only take pages on LRU: a check now makes later tests safe */ > + if (!PageLRU(page)) > + goto isolate_fail_put; > + > + /* Compaction might skip unevictable pages but CMA takes them */ > + if (!(mode & ISOLATE_UNEVICTABLE) && PageUnevictable(page)) > + goto isolate_fail_put; > + > + /* > + * To minimise LRU disruption, the caller can indicate with > + * ISOLATE_ASYNC_MIGRATE that it only wants to isolate pages > + * it will be able to migrate without blocking - clean pages > + * for the most part. PageWriteback would require blocking. > + */ > + if ((mode & ISOLATE_ASYNC_MIGRATE) && PageWriteback(page)) > goto isolate_fail_put; > > + if ((mode & ISOLATE_ASYNC_MIGRATE) && PageDirty(page)) { > + bool migrate_dirty; > + > + /* > + * Only pages without mappings or that have a > + * ->migratepage callback are possible to migrate > + * without blocking. However, we can be racing with > + * truncation so it's necessary to lock the page > + * to stabilise the mapping as truncation holds > + * the page lock until after the page is removed > + * from the page cache. > + */ > + if (!trylock_page(page)) > + goto isolate_fail_put; > + > + mapping = page_mapping(page); > + migrate_dirty = !mapping || mapping->a_ops->migratepage; > + unlock_page(page); > + if (!migrate_dirty) > + goto isolate_fail_put; > + } > + > /* Try isolate the page */ > if (!TestClearPageLRU(page)) > goto isolate_fail_put; > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2009,69 +2009,6 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone, > } > > /* > - * Attempt to remove the specified page from its LRU. Only take this page > - * if it is of the appropriate PageActive status. Pages which are being > - * freed elsewhere are also ignored. > - * > - * page: page to consider > - * mode: one of the LRU isolation modes defined above > - * > - * returns true on success, false on failure. > - */ > -bool __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode) > -{ > - /* Only take pages on the LRU. */ > - if (!PageLRU(page)) > - return false; > - > - /* Compaction should not handle unevictable pages but CMA can do so */ > - if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE)) > - return false; > - > - /* > - * To minimise LRU disruption, the caller can indicate that it only > - * wants to isolate pages it will be able to operate on without > - * blocking - clean pages for the most part. > - * > - * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages > - * that it is possible to migrate without blocking > - */ > - if (mode & ISOLATE_ASYNC_MIGRATE) { > - /* All the caller can do on PageWriteback is block */ > - if (PageWriteback(page)) > - return false; > - > - if (PageDirty(page)) { > - struct address_space *mapping; > - bool migrate_dirty; > - > - /* > - * Only pages without mappings or that have a > - * ->migratepage callback are possible to migrate > - * without blocking. However, we can be racing with > - * truncation so it's necessary to lock the page > - * to stabilise the mapping as truncation holds > - * the page lock until after the page is removed > - * from the page cache. > - */ > - if (!trylock_page(page)) > - return false; > - > - mapping = page_mapping(page); > - migrate_dirty = !mapping || mapping->a_ops->migratepage; > - unlock_page(page); > - if (!migrate_dirty) > - return false; > - } > - } > - > - if ((mode & ISOLATE_UNMAPPED) && page_mapped(page)) > - return false; > - > - return true; > -} > - > -/* > * Update LRU sizes after isolating pages. The LRU size updates must > * be complete before mem_cgroup_update_lru_size due to a sanity check. > */ > @@ -2122,11 +2059,11 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, > unsigned long skipped = 0; > unsigned long scan, total_scan, nr_pages; > LIST_HEAD(pages_skipped); > - isolate_mode_t mode = (sc->may_unmap ? 0 : ISOLATE_UNMAPPED); > > total_scan = 0; > scan = 0; > while (scan < nr_to_scan && !list_empty(src)) { > + struct list_head *move_to = src; > struct page *page; > > page = lru_to_page(src); > @@ -2136,9 +2073,9 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, > total_scan += nr_pages; > > if (page_zonenum(page) > sc->reclaim_idx) { > - list_move(&page->lru, &pages_skipped); > nr_skipped[page_zonenum(page)] += nr_pages; > - continue; > + move_to = &pages_skipped; > + goto move; > } > > /* > @@ -2146,37 +2083,34 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, > * return with no isolated pages if the LRU mostly contains > * ineligible pages. This causes the VM to not reclaim any > * pages, triggering a premature OOM. > - * > - * Account all tail pages of THP. This would not cause > - * premature OOM since __isolate_lru_page() returns -EBUSY > - * only when the page is being freed somewhere else. > + * Account all tail pages of THP. > */ > scan += nr_pages; > - if (!__isolate_lru_page_prepare(page, mode)) { > - /* It is being freed elsewhere */ > - list_move(&page->lru, src); > - continue; > - } > + > + if (!PageLRU(page)) > + goto move; > + if (!sc->may_unmap && page_mapped(page)) > + goto move; > + > /* > * Be careful not to clear PageLRU until after we're > * sure the page is not being freed elsewhere -- the > * page release code relies on it. > */ > - if (unlikely(!get_page_unless_zero(page))) { > - list_move(&page->lru, src); > - continue; > - } > + if (unlikely(!get_page_unless_zero(page))) > + goto move; > > if (!TestClearPageLRU(page)) { > /* Another thread is already isolating this page */ > put_page(page); > - list_move(&page->lru, src); > - continue; > + goto move; > } > > nr_taken += nr_pages; > nr_zone_taken[page_zonenum(page)] += nr_pages; > - list_move(&page->lru, dst); > + move_to = dst; > +move: > + list_move(&page->lru, move_to); > } > > /* > @@ -2200,7 +2134,8 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, > } > *nr_scanned = total_scan; > trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan, > - total_scan, skipped, nr_taken, mode, lru); > + total_scan, skipped, nr_taken, > + sc->may_unmap ? 0 : ISOLATE_UNMAPPED, lru); > update_lru_sizes(lruvec, lru, nr_zone_taken); > return nr_taken; > }
--- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -386,7 +386,6 @@ extern void lru_cache_add_inactive_or_unevictable(struct page *page, extern unsigned long zone_reclaimable_pages(struct zone *zone); extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order, gfp_t gfp_mask, nodemask_t *mask); -extern bool __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode); extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, unsigned long nr_pages, gfp_t gfp_mask, --- a/mm/compaction.c +++ b/mm/compaction.c @@ -785,7 +785,7 @@ static bool too_many_isolated(pg_data_t *pgdat) * @cc: Compaction control structure. * @low_pfn: The first PFN to isolate * @end_pfn: The one-past-the-last PFN to isolate, within same pageblock - * @isolate_mode: Isolation mode to be used. + * @mode: Isolation mode to be used. * * Isolate all pages that can be migrated from the range specified by * [low_pfn, end_pfn). The range is expected to be within same pageblock. @@ -798,7 +798,7 @@ static bool too_many_isolated(pg_data_t *pgdat) */ static int isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, - unsigned long end_pfn, isolate_mode_t isolate_mode) + unsigned long end_pfn, isolate_mode_t mode) { pg_data_t *pgdat = cc->zone->zone_pgdat; unsigned long nr_scanned = 0, nr_isolated = 0; @@ -806,6 +806,7 @@ static bool too_many_isolated(pg_data_t *pgdat) unsigned long flags = 0; struct lruvec *locked = NULL; struct page *page = NULL, *valid_page = NULL; + struct address_space *mapping; unsigned long start_pfn = low_pfn; bool skip_on_failure = false; unsigned long next_skip_pfn = 0; @@ -990,7 +991,7 @@ static bool too_many_isolated(pg_data_t *pgdat) locked = NULL; } - if (!isolate_movable_page(page, isolate_mode)) + if (!isolate_movable_page(page, mode)) goto isolate_success; } @@ -1002,15 +1003,15 @@ static bool too_many_isolated(pg_data_t *pgdat) * so avoid taking lru_lock and isolating it unnecessarily in an * admittedly racy check. */ - if (!page_mapping(page) && - page_count(page) > page_mapcount(page)) + mapping = page_mapping(page); + if (!mapping && page_count(page) > page_mapcount(page)) goto isolate_fail; /* * Only allow to migrate anonymous pages in GFP_NOFS context * because those do not depend on fs locks. */ - if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page)) + if (!(cc->gfp_mask & __GFP_FS) && mapping) goto isolate_fail; /* @@ -1021,9 +1022,45 @@ static bool too_many_isolated(pg_data_t *pgdat) if (unlikely(!get_page_unless_zero(page))) goto isolate_fail; - if (!__isolate_lru_page_prepare(page, isolate_mode)) + /* Only take pages on LRU: a check now makes later tests safe */ + if (!PageLRU(page)) + goto isolate_fail_put; + + /* Compaction might skip unevictable pages but CMA takes them */ + if (!(mode & ISOLATE_UNEVICTABLE) && PageUnevictable(page)) + goto isolate_fail_put; + + /* + * To minimise LRU disruption, the caller can indicate with + * ISOLATE_ASYNC_MIGRATE that it only wants to isolate pages + * it will be able to migrate without blocking - clean pages + * for the most part. PageWriteback would require blocking. + */ + if ((mode & ISOLATE_ASYNC_MIGRATE) && PageWriteback(page)) goto isolate_fail_put; + if ((mode & ISOLATE_ASYNC_MIGRATE) && PageDirty(page)) { + bool migrate_dirty; + + /* + * Only pages without mappings or that have a + * ->migratepage callback are possible to migrate + * without blocking. However, we can be racing with + * truncation so it's necessary to lock the page + * to stabilise the mapping as truncation holds + * the page lock until after the page is removed + * from the page cache. + */ + if (!trylock_page(page)) + goto isolate_fail_put; + + mapping = page_mapping(page); + migrate_dirty = !mapping || mapping->a_ops->migratepage; + unlock_page(page); + if (!migrate_dirty) + goto isolate_fail_put; + } + /* Try isolate the page */ if (!TestClearPageLRU(page)) goto isolate_fail_put; --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2009,69 +2009,6 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone, } /* - * Attempt to remove the specified page from its LRU. Only take this page - * if it is of the appropriate PageActive status. Pages which are being - * freed elsewhere are also ignored. - * - * page: page to consider - * mode: one of the LRU isolation modes defined above - * - * returns true on success, false on failure. - */ -bool __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode) -{ - /* Only take pages on the LRU. */ - if (!PageLRU(page)) - return false; - - /* Compaction should not handle unevictable pages but CMA can do so */ - if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE)) - return false; - - /* - * To minimise LRU disruption, the caller can indicate that it only - * wants to isolate pages it will be able to operate on without - * blocking - clean pages for the most part. - * - * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages - * that it is possible to migrate without blocking - */ - if (mode & ISOLATE_ASYNC_MIGRATE) { - /* All the caller can do on PageWriteback is block */ - if (PageWriteback(page)) - return false; - - if (PageDirty(page)) { - struct address_space *mapping; - bool migrate_dirty; - - /* - * Only pages without mappings or that have a - * ->migratepage callback are possible to migrate - * without blocking. However, we can be racing with - * truncation so it's necessary to lock the page - * to stabilise the mapping as truncation holds - * the page lock until after the page is removed - * from the page cache. - */ - if (!trylock_page(page)) - return false; - - mapping = page_mapping(page); - migrate_dirty = !mapping || mapping->a_ops->migratepage; - unlock_page(page); - if (!migrate_dirty) - return false; - } - } - - if ((mode & ISOLATE_UNMAPPED) && page_mapped(page)) - return false; - - return true; -} - -/* * Update LRU sizes after isolating pages. The LRU size updates must * be complete before mem_cgroup_update_lru_size due to a sanity check. */ @@ -2122,11 +2059,11 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, unsigned long skipped = 0; unsigned long scan, total_scan, nr_pages; LIST_HEAD(pages_skipped); - isolate_mode_t mode = (sc->may_unmap ? 0 : ISOLATE_UNMAPPED); total_scan = 0; scan = 0; while (scan < nr_to_scan && !list_empty(src)) { + struct list_head *move_to = src; struct page *page; page = lru_to_page(src); @@ -2136,9 +2073,9 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, total_scan += nr_pages; if (page_zonenum(page) > sc->reclaim_idx) { - list_move(&page->lru, &pages_skipped); nr_skipped[page_zonenum(page)] += nr_pages; - continue; + move_to = &pages_skipped; + goto move; } /* @@ -2146,37 +2083,34 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, * return with no isolated pages if the LRU mostly contains * ineligible pages. This causes the VM to not reclaim any * pages, triggering a premature OOM. - * - * Account all tail pages of THP. This would not cause - * premature OOM since __isolate_lru_page() returns -EBUSY - * only when the page is being freed somewhere else. + * Account all tail pages of THP. */ scan += nr_pages; - if (!__isolate_lru_page_prepare(page, mode)) { - /* It is being freed elsewhere */ - list_move(&page->lru, src); - continue; - } + + if (!PageLRU(page)) + goto move; + if (!sc->may_unmap && page_mapped(page)) + goto move; + /* * Be careful not to clear PageLRU until after we're * sure the page is not being freed elsewhere -- the * page release code relies on it. */ - if (unlikely(!get_page_unless_zero(page))) { - list_move(&page->lru, src); - continue; - } + if (unlikely(!get_page_unless_zero(page))) + goto move; if (!TestClearPageLRU(page)) { /* Another thread is already isolating this page */ put_page(page); - list_move(&page->lru, src); - continue; + goto move; } nr_taken += nr_pages; nr_zone_taken[page_zonenum(page)] += nr_pages; - list_move(&page->lru, dst); + move_to = dst; +move: + list_move(&page->lru, move_to); } /* @@ -2200,7 +2134,8 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, } *nr_scanned = total_scan; trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan, - total_scan, skipped, nr_taken, mode, lru); + total_scan, skipped, nr_taken, + sc->may_unmap ? 0 : ISOLATE_UNMAPPED, lru); update_lru_sizes(lruvec, lru, nr_zone_taken); return nr_taken; }
__isolate_lru_page_prepare() conflates two unrelated functions, with the flags to one disjoint from the flags to the other; and hides some of the important checks outside of isolate_migratepages_block(), where the sequence is better to be visible. It comes from the days of lumpy reclaim, before compaction, when the combination made more sense. Move what's needed by mm/compaction.c isolate_migratepages_block() inline there, and what's needed by mm/vmscan.c isolate_lru_pages() inline there. Shorten "isolate_mode" to "mode", so the sequence of conditions is easier to read. Declare a "mapping" variable, to save one call to page_mapping() (but not another: calling again after page is locked is necessary). Simplify isolate_lru_pages() with a "move_to" list pointer. Signed-off-by: Hugh Dickins <hughd@google.com> --- include/linux/swap.h | 1 - mm/compaction.c | 51 ++++++++++++++++++++++---- mm/vmscan.c | 101 +++++++++------------------------------------------ 3 files changed, 62 insertions(+), 91 deletions(-)