Messages in this thread Patch in this message | | | Subject | Re: [v4 PATCH 1/2] mm: vmscan: remove double slab pressure by inc'ing sc->nr_scanned | From | Yang Shi <> | Date | Fri, 24 May 2019 13:37:56 +0800 |
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On 5/24/19 12:15 PM, Hillf Danton wrote: > On Thu, 23 May 2019 10:27:37 +0800 Yang Shi wrote: >> The commit 9092c71bb724 ("mm: use sc->priority for slab shrink targets") >> has broken up the relationship between sc->nr_scanned and slab pressure. >> The sc->nr_scanned can't double slab pressure anymore. So, it sounds no >> sense to still keep sc->nr_scanned inc'ed. Actually, it would prevent >> from adding pressure on slab shrink since excessive sc->nr_scanned would >> prevent from scan->priority raise. >> > The deleted code below wants to get more slab pages shrinked, and it can do > that without raising scan priority first even after commit 9092c71bb724. Or > we may face the risk that priority goes up too much faster than thought, per > the following snippet.
The priority is raised if kswapd_shrink_node() returns false for kswapd (The direct reclaim would just raise the priority if sc->nr_reclaimed >= sc->nr_to_reclaim). The kswapd_shrink_node() returns "return sc->nr_scanned >= sc->nr_to_reclaim". So, the old "double pressure" doesn't work as it was designed anymore since it would prevent from make "sc->nr_scanned < sc->nr_to_reclaim".
And, the patch 2/2 would not make the priority go up too much since one THP would be accounted as 512 base page.
> > /* > * If we're getting trouble reclaiming, start doing > * writepage even in laptop mode. > */ > if (sc->priority < DEF_PRIORITY - 2) > >> The bonnie test doesn't show this would change the behavior of >> slab shrinkers. >> >> w/ w/o >> /sec %CP /sec %CP >> Sequential delete: 3960.6 94.6 3997.6 96.2 >> Random delete: 2518 63.8 2561.6 64.6 >> >> The slight increase of "/sec" without the patch would be caused by the >> slight increase of CPU usage. >> >> Cc: Josef Bacik <josef@toxicpanda.com> >> Cc: Michal Hocko <mhocko@kernel.org> >> Acked-by: Johannes Weiner <hannes@cmpxchg.org> >> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> >> --- >> v4: Added Johannes's ack >> >> mm/vmscan.c | 5 ----- >> 1 file changed, 5 deletions(-) >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index 7acd0af..b65bc50 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -1137,11 +1137,6 @@ static unsigned long shrink_page_list(struct list_head *page_list, >> if (!sc->may_unmap && page_mapped(page)) >> goto keep_locked; >> >> - /* Double the slab pressure for mapped and swapcache pages */ >> - if ((page_mapped(page) || PageSwapCache(page)) && >> - !(PageAnon(page) && !PageSwapBacked(page))) >> - sc->nr_scanned++; >> - >> may_enter_fs = (sc->gfp_mask & __GFP_FS) || >> (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO)); >> >> -- >> 1.8.3.1 >> > Best Regards > Hillf
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