Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | From | Vinayak Menon <> | Subject | [PATCH v6] mm: vmscan: do not pass reclaimed slab to vmpressure | Date | Thu, 23 Feb 2017 14:52:50 +0530 |
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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. In this use case, The number of critical vmpressure events received is around 50% less on 4.4 than 3.18. 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. The difference in reclaim behaviour is because of lesser number of kills and kills happening late, resulting in more swapping and page cache reclaim.
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
The lowmemorykiller example above is just for indicating the difference in vmpressure events between 4.4 and 3.18.
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. 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()") Link: http://lkml.kernel.org/r/1486641577-11685-2-git-send-email-vinmenon@codeaurora.org Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Vinayak Menon <vinmenon@codeaurora.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> --- v6: Modifying the changelog as per Michal's suggestion
mm/vmscan.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c index 70aa739..26c3b40 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2603,16 +2603,23 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc) sc->nr_scanned - nr_scanned, node_lru_pages); + /* + * Record the subtree's reclaim efficiency. The reclaimed + * pages from slab is excluded here because the corresponding + * scanned pages is not accounted. Moreover, freeing 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. + */ + vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true, + sc->nr_scanned - nr_scanned, + sc->nr_reclaimed - nr_reclaimed); + if (reclaim_state) { sc->nr_reclaimed += reclaim_state->reclaimed_slab; reclaim_state->reclaimed_slab = 0; } - /* Record the subtree's reclaim efficiency */ - vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true, - sc->nr_scanned - nr_scanned, - sc->nr_reclaimed - nr_reclaimed); - if (sc->nr_reclaimed - nr_reclaimed) reclaimable = true; -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation
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