During global reclaim, the nr_reclaimed passed to vmpressure includes the
pages reclaimed from slab. But the corresponding scanned slab pages is
not passed. There is an impact to the vmpressure values because of this.
While moving from kernel version 3.18 to 4.4, a difference is seen in the
vmpressure values for the same workload resulting in a different behaviour
of the vmpressure consumer. One such case is of a vmpressure based
lowmemorykiller. It is observed that the vmpressure events are received
late and less in number resulting in tasks not being killed at the right
time. The following numbers show the impact on reclaim activity due to
the change in behaviour of lowmemorykiller on a 4GB device. The test
launches a number of apps in sequence and repeats it multiple times.
v4.4 v3.18
pgpgin 163016456 145617236
pgpgout 4366220 4188004
workingset_refault 29857868 26781854
workingset_activate 6293946 5634625
pswpin 1327601 1133912
pswpout 3593842 3229602
pgalloc_dma 99520618 94402970
pgalloc_normal 104046854 98124798
pgfree 203772640 192600737
pgmajfault 2126962 1851836
pgsteal_kswapd_dma 19732899 18039462
pgsteal_kswapd_normal 19945336 17977706
pgsteal_direct_dma 206757 131376
pgsteal_direct_normal 236783 138247
pageoutrun 116622 108370
allocstall 7220 4684
compact_stall 931 856
This is a regression introduced by commit 6b4f7799c6 ("mm: vmscan:
invoke slab shrinkers from shrink_zone()").
So do not consider reclaimed slab pages for vmpressure calculation. The
reclaimed pages from slab can be excluded because the freeing of a page by
slab shrinking depends on each slab's object population, making the cost
model (i.e. scan:free) different from that of LRU. Also, not every
shrinker accounts the pages it reclaims. But ideally the pages reclaimed
from slab should be passed to vmpressure, otherwise higher vmpressure
levels can be triggered even when there is a reclaim progress. But
accounting only the reclaimed slab pages without the scanned, and adding
something which does not fit into the cost model just adds noise to the
vmpressure values.
Fixes: 6b4f7799c6 ("mm: vmscan: invoke slab shrinkers from shrink_zone()")
Link: http://lkml.kernel.org/r/1486641577-11685-2-git-send-email-vinmenon@codeaurora.org
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Anton Vorontsov <anton.vorontsov@linaro.org>
Cc: Shiraz Hashim <shashim@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Git-commit: 97a9668a428e9651a4aa3ff5d4e7e60024be2d87
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
Change-Id: If46b1cee6fd9723bebd87d76e0bb8451de05a9c1
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
280a2d3683