From d99fd5feb0ac1d56c36c760a8d922a46bd6c5521 Mon Sep 17 00:00:00 2001 From: Alex Shi <alex.shi@linux.alibaba.com> Date: Wed, 24 Feb 2021 12:09:25 -0800 Subject: [PATCH] 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> --- mm/compaction.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index 3aef10c61d0ec..69ca3d6f97644 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -995,7 +995,6 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, if (!TestClearPageLRU(page)) goto isolate_fail_put; - rcu_read_lock(); lruvec = mem_cgroup_page_lruvec(page, pgdat); /* 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); locked = lruvec; - rcu_read_unlock(); lruvec_memcg_debug(lruvec, page); @@ -1026,8 +1024,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, SetPageLRU(page); goto isolate_fail_put; } - } else - rcu_read_unlock(); + } /* The whole page is taken off the LRU; skip the tail pages. */ if (PageCompound(page)) -- 2.30.2