tree 45a3cbb1ece11f08072eb2b64c5e9d581a380b5f
parent 6ce54268d743ed8c7c03f8b475ff1f19f50cf128
author Vinayak Menon <vinmenon@codeaurora.org> 1487494831 +1100
committer Patrick Daly <pdaly@codeaurora.org> 1493322948 -0700

mm: vmscan: do not pass reclaimed slab to vmpressure

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 6b4f7799c6a5 ("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: 6b4f7799c6a5
("mm: vmscan: invoke slab shrinkers from shrink_zone()")
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>
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>