[PATCH 5.10 006/106] mm: __isolate_lru_page_prepare() in isolate_migratepages_block()

Greg Kroah-Hartman
2022-12-12T13:12:56Z

From: Hugh Dickins <hughd@google.com>

[ Upstream commit 89f6c88a6ab4a11deb14c270f7f1454cda4f73d6 ]

__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.

Link: https://lkml.kernel.org/r/879d62a8-91cc-d3c6-fb3b-69768236df68@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: David Rientjes <rientjes@google.com>
Reviewed-by: Alex Shi <alexs@kernel.org>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Stable-dep-of: 829ae0f81ce0 ("mm: migrate: fix THP's mapcount on isolation")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/swap.h | 1 -
mm/compaction.c | 51 +++++++++++++++++++---
mm/vmscan.c | 101 ++++++++-----------------------------------
3 files changed, 62 insertions(+), 91 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 394d5de5d4b4..a502928c29c5 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -358,7 +358,6 @@ 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,
diff --git a/mm/compaction.c b/mm/compaction.c
index ea46aadc7c21..57ce6b001b10 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -784,7 +784,7 @@ 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 unsigned long
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 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
unsigned long flags = 0;
bool locked = false;
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;
@@ -949,7 +950,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
locked = false;
}

- if (!isolate_movable_page(page, isolate_mode))
+ if (!isolate_movable_page(page, mode))
goto isolate_success;
}

@@ -961,15 +962,15 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
* 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;

/*
@@ -980,9 +981,45 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
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;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 00a47845a15b..9cba0f890b33 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1535,69 +1535,6 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
return nr_reclaimed;
}

-/*
- * 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.
@@ -1647,11 +1584,11 @@ 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);
@@ -1661,9 +1598,9 @@ 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;
}

/*
@@ -1671,37 +1608,34 @@ 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);
}

/*
@@ -1725,7 +1659,8 @@ 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;
}
--
2.35.1