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BACKPORT: FROMLIST: mm: disable LRU pagevec during the migration temporarily

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LRU pagevec holds refcount of pages until the pagevec are drained.
It could prevent migration since the refcount of the page is greater
than the expection in migration logic. To mitigate the issue,
callers of migrate_pages drains LRU pagevec via migrate_prep or
lru_add_drain_all before migrate_pages call.

However, it's not enough because pages coming into pagevec after the
draining call still could stay at the pagevec so it could keep
preventing page migration. Since some callers of migrate_pages have
retrial logic with LRU draining, the page would migrate at next trail
but it is still fragile in that it doesn't close the fundamental race
between upcoming LRU pages into pagvec and migration so the migration
failure could cause contiguous memory allocation failure in the end.

To close the race, this patch disables lru caches(i.e, pagevec)
during ongoing migration until migrate is done.

Since it's really hard to reproduce, I measured how many times
migrate_pages retried with force mode(it is about a fallback to a
sync migration) with below debug code.

int migrate_pages(struct list_head *from, new_page_t get_new_page,
			..
			..

if (rc && reason == MR_CONTIG_RANGE && pass > 2) {
       printk(KERN_ERR, "pfn 0x%lx reason %d\n", page_to_pfn(page), rc);
       dump_page(page, "fail to migrate");
}

The test was repeating android apps launching with cma allocation
in background every five seconds. Total cma allocation count was
about 500 during the testing. With this patch, the dump_page count
was reduced from 400 to 30.

The new interface is also useful for memory hotplug which currently
drains lru pcp caches after each migration failure. This is rather
suboptimal as it has to disrupt others running during the operation.
With the new interface the operation happens only once. This is also in
line with pcp allocator cache which are disabled for the offlining as
well.

Bug: 180018981
Link: https://lore.kernel.org/linux-mm/20210319175127.886124-1-minchan@kernel.org/
Reviewed-by: Chris Goldsworthy <cgoldswo@codeaurora.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Minchan Kim <minchan@google.com>
Change-Id: I838c63d11ca49a8734d8b37a7d5272ab6b802f9f
This commit is contained in:
Minchan Kim
2021-03-19 12:39:51 -07:00
committed by Suren Baghdasaryan
parent d3c1bf42af
commit 68a4731181
7 changed files with 86 additions and 14 deletions
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2
include/linux/migrate.h
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@@ -46,6 +46,7 @@ extern int isolate_movable_page(struct page *page, isolate_mode_t mode);
extern void putback_movable_page(struct page *page);
extern void migrate_prep(void);
extern void migrate_finish(void);
extern void migrate_prep_local(void);
extern void migrate_page_states(struct page *newpage, struct page *page);
extern void migrate_page_copy(struct page *newpage, struct page *page);
@@ -67,6 +68,7 @@ static inline int isolate_movable_page(struct page *page, isolate_mode_t mode)
{ return -EBUSY; }
static inline int migrate_prep(void) { return -ENOSYS; }
static inline int migrate_finish(void) { return -ENOSYS; }
static inline int migrate_prep_local(void) { return -ENOSYS; }
static inline void migrate_page_states(struct page *newpage, struct page *page)