linux-kernel - [PATCH v2 3/3] mm/compaction: remove rcu_read

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Message-Id: <1608614453-10739-3-git-send-email-alex.shi@linux.alibaba.com>
Date:   Tue, 22 Dec 2020 13:20:53 +0800
From:   Alex Shi <alex.shi@...ux.alibaba.com>
To:     hughd@...gle.com
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 3/3] 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 Dickin' helped on commit log polishing, Thanks!

Signed-off-by: Alex Shi <alex.shi@...ux.alibaba.com>
Acked-by: Hugh Dickins <hughd@...gle.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
---
 mm/compaction.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 8049d3530812..02af220fb992 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))
-- 
2.29.GIT