Commit 9a9b6cce authored Apr 01, 2020 by Yang Shi Committed by Linus Torvalds Apr 02, 2020

mm: swap: use smp_mb__after_atomic() to order LRU bit set



Memory barrier is needed after setting LRU bit, but smp_mb() is too
strong.  Some architectures, i.e.  x86, imply memory barrier with atomic
operations, so replacing it with smp_mb__after_atomic() sounds better,
which is nop on strong ordered machines, and full memory barriers on
others.  With this change the vm-scalability cases would perform better on
x86, I saw total 6% improvement with this patch and previous inline fix.

The test data (lru-file-readtwice throughput) against v5.6-rc4:
	mainline	w/ inline fix	w/ both (adding this)
	150MB		154MB		159MB

Fixes: 9c4e6b1a ("mm, mlock, vmscan: no more skipping pagevecs")
Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Shakeel Butt <shakeelb@google.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: http://lkml.kernel.org/r/1584500541-46817-2-git-send-email-yang.shi@linux.alibaba.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 1eb6234e

mm/swap.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -931,7 +931,6 @@ static void __pagevec_lru_add_fn(struct page page, struct lruvec lruvec,

		VM_BUG_ON_PAGE(PageLRU(page), page);

		SetPageLRU(page);
		/*
		* Page becomes evictable in two ways:
		* 1) Within LRU lock [munlock_vma_page() and __munlock_pagevec()].
		@@ -958,7 +957,8 @@ static void __pagevec_lru_add_fn(struct page page, struct lruvec lruvec,
		* looking at the same page) and the evictable page will be stranded
		* in an unevictable LRU.
		*/
		smp_mb();
		SetPageLRU(page);
		smp_mb__after_atomic();

		if (page_evictable(page)) {
		lru = page_lru(page);

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