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mm/compaction: fix misbehaviors of fast_find_migrateblock() 

In the fast_find_migrateblock(), it iterates ocer the freelist to find the
proper pageblock.  But there are some misbehaviors.

First, if the page we found is equal to cc->migrate_pfn, it is considered
that we didn't find a suitable pageblock.  Secondly, if the loop was
terminated because order is less than PAGE_ALLOC_COSTLY_ORDER, it could be
considered that we found a suitable one.  Thirdly, if the skip bit is set
on the page block and we goto continue, it doesn't check nr_scanned.
Fourthly, if the page block's skip bit is set, it checks that page block
is the last of list, which is unnecessary.

Link: https://lkml.kernel.org/r/20210128130411.6125-1-vvghjk1234@gmail.com
Fixes: 70b44595ea ("mm, compaction: use free lists to quickly locate a migration source")
Signed-off-by: Wonhyuk Yang <vvghjk1234@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Wonhyuk Yang 2021-02-24 12:09:36 -08:00 committed by Linus Torvalds
parent 40d7e20320
commit 15d28d0d11
1 changed files with 12 additions and 15 deletions
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27
mm/compaction.c
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@ -1698,6 +1698,7 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
unsigned long pfn = cc->migrate_pfn; unsigned long pfn = cc->migrate_pfn;
unsigned long high_pfn; unsigned long high_pfn;
int order; int order;
bool found_block = false;
/* Skip hints are relied on to avoid repeats on the fast search */ /* Skip hints are relied on to avoid repeats on the fast search */
if (cc->ignore_skip_hint) if (cc->ignore_skip_hint)
@ -1740,7 +1741,7 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance); high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance);
for (order = cc->order - 1; for (order = cc->order - 1;
order >= PAGE_ALLOC_COSTLY_ORDER && pfn == cc->migrate_pfn && nr_scanned < limit; order >= PAGE_ALLOC_COSTLY_ORDER && !found_block && nr_scanned < limit;
order--) { order--) {
struct free_area *area = &cc->zone->free_area[order]; struct free_area *area = &cc->zone->free_area[order];
struct list_head *freelist; struct list_head *freelist;
@ -1755,7 +1756,11 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
list_for_each_entry(freepage, freelist, lru) { list_for_each_entry(freepage, freelist, lru) {
unsigned long free_pfn; unsigned long free_pfn;
nr_scanned++; if (nr_scanned++ >= limit) {
move_freelist_tail(freelist, freepage);
break;
}
free_pfn = page_to_pfn(freepage); free_pfn = page_to_pfn(freepage);
if (free_pfn < high_pfn) { if (free_pfn < high_pfn) {
/* /*
@ -1764,12 +1769,8 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
* the list assumes an entry is deleted, not * the list assumes an entry is deleted, not
* reordered. * reordered.
*/ */
if (get_pageblock_skip(freepage)) { if (get_pageblock_skip(freepage))
if (list_is_last(freelist, &freepage->lru))
break;
continue; continue;
}
/* Reorder to so a future search skips recent pages */ /* Reorder to so a future search skips recent pages */
move_freelist_tail(freelist, freepage); move_freelist_tail(freelist, freepage);
@ -1777,15 +1778,10 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
update_fast_start_pfn(cc, free_pfn); update_fast_start_pfn(cc, free_pfn);
pfn = pageblock_start_pfn(free_pfn); pfn = pageblock_start_pfn(free_pfn);
cc->fast_search_fail = 0; cc->fast_search_fail = 0;
found_block = true;
set_pageblock_skip(freepage); set_pageblock_skip(freepage);
break; break;
} }
if (nr_scanned >= limit) {
cc->fast_search_fail++;
move_freelist_tail(freelist, freepage);
break;
}
} }
spin_unlock_irqrestore(&cc->zone->lock, flags); spin_unlock_irqrestore(&cc->zone->lock, flags);
} }
@ -1796,9 +1792,10 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
* If fast scanning failed then use a cached entry for a page block * If fast scanning failed then use a cached entry for a page block
* that had free pages as the basis for starting a linear scan. * that had free pages as the basis for starting a linear scan.
*/ */
if (pfn == cc->migrate_pfn) if (!found_block) {
cc->fast_search_fail++;
pfn = reinit_migrate_pfn(cc); pfn = reinit_migrate_pfn(cc);
}
return pfn; return pfn;
} }