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mm/compaction: remove rcu_read_lock during page compaction 

isolate_migratepages_block() used rcu_read_lock() with the intention of
safeguarding against the mem_cgroup being destroyed concurrently; but
its TestClearPageLRU already protects against that.  Delete the
unnecessary rcu_read_lock() and _unlock().

Hugh Dickins helped on commit log polishing, Thanks!

Link: https://lkml.kernel.org/r/1608614453-10739-3-git-send-email-alex.shi@linux.alibaba.com
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Alex Shi 2021-02-24 12:09:25 -08:00 committed by Linus Torvalds
parent c457cd96f1
commit d99fd5feb0
1 changed files with 1 additions and 4 deletions
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5
mm/compaction.c
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@ -995,7 +995,6 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
if (!TestClearPageLRU(page)) if (!TestClearPageLRU(page))
goto isolate_fail_put; goto isolate_fail_put;
rcu_read_lock();
lruvec = mem_cgroup_page_lruvec(page, pgdat); lruvec = mem_cgroup_page_lruvec(page, pgdat);
/* If we already hold the lock, we can skip some rechecking */ /* If we already hold the lock, we can skip some rechecking */
@ -1005,7 +1004,6 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
compact_lock_irqsave(&lruvec->lru_lock, &flags, cc); compact_lock_irqsave(&lruvec->lru_lock, &flags, cc);
locked = lruvec; locked = lruvec;
rcu_read_unlock();
lruvec_memcg_debug(lruvec, page); lruvec_memcg_debug(lruvec, page);
@ -1026,8 +1024,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
SetPageLRU(page); SetPageLRU(page);
goto isolate_fail_put; goto isolate_fail_put;
} }
} else }
rcu_read_unlock();
/* The whole page is taken off the LRU; skip the tail pages. */ /* The whole page is taken off the LRU; skip the tail pages. */
if (PageCompound(page)) if (PageCompound(page))