Commit 4167e9b2cf10 ("mm: remove GFP_THISNODE") removed the
GFP_THISNODE flag combination due to confusing semantics. It noted that
alloc_misplaced_dst_page() was one such user after changes made by commit
e97ca8e5b864 ("mm: fix GFP_THISNODE callers and clarify"). Unfortunately
when GFP_THISNODE was removed, users of alloc_misplaced_dst_page() started
waking kswapd and entering direct reclaim because the wrong GFP flags are
cleared. The consequence is that workloads that used to fit into memory
now get reclaimed which is addressed by this patch.
The problem can be demonstrated with "mutilate" that exercises memcached
which is software dedicated to memory object caching. The configuration
uses 80% of memory and is run 3 times for varying numbers of clients. The
results on a 4-socket NUMA box are
mutilate
4.4.0 4.4.0
vanilla numaswap-v1
Hmean 1 8394.71 ( 0.00%) 8395.32 ( 0.01%)
Hmean 4 30024.62 ( 0.00%) 34513.54 ( 14.95%)
Hmean 7 32821.08 ( 0.00%) 70542.96 (114.93%)
Hmean 12 55229.67 ( 0.00%) 93866.34 ( 69.96%)
Hmean 21 39438.96 ( 0.00%) 85749.21 (117.42%)
Hmean 30 37796.10 ( 0.00%) 50231.49 ( 32.90%)
Hmean 47 18070.91 ( 0.00%) 38530.13 (113.22%)
The metric is queries/second with the more the better. The results are way
outside of the noise and the reason for the improvement is obvious from
some of the vmstats
4.4.0 4.4.0
vanillanumaswap-v1r1
Minor Faults 1929399272 2146148218
Major Faults 19746529 3567
Swap Ins 57307366 9913
Swap Outs 50623229 17094
Allocation stalls 35909 443
DMA allocs 0 0
DMA32 allocs 72976349 170567396
Normal allocs 5306640898 5310651252
Movable allocs 0 0
Direct pages scanned 404130893 799577
Kswapd pages scanned 160230174 0
Kswapd pages reclaimed 55928786 0
Direct pages reclaimed 1843936 41921
Page writes file 2391 0
Page writes anon 50623229 17094
The vanilla kernel is swapping like crazy with large amounts of
direct reclaim and kswapd activity. The figures are aggregate but it's
known that the bad activity is throughout the entire test.
Note that simple streaming anon/file memory consumers also see this problem
but it's not as obvious. In those cases, kswapd is awake when it should
not be.
As there are at least two reclaim-related bugs out there, it's worth spelling
out the user-visible impact. This patch only addresses bugs related to
excessive reclaim on NUMA hardware when the working set is larger than a NUMA
node. There is a bug related to high kswapd CPU usage but the reports are
against laptops and other UMA hardware and is not addressed by this patch.
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v4.1+
---
mm/migrate.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/migrate.c b/mm/migrate.c
index 7890d0bb5e23..6d17e0ab42d4 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1578,7 +1578,7 @@ static struct page *alloc_misplaced_dst_page(struct page *page,
(GFP_HIGHUSER_MOVABLE |
__GFP_THISNODE | __GFP_NOMEMALLOC |
__GFP_NORETRY | __GFP_NOWARN) &
- ~(__GFP_IO | __GFP_FS), 0);
+ ~__GFP_RECLAIM, 0);
return newpage;
}
--
2.6.4
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