linux-kernel - Re: [PATCH v3 2/9] mm/vmscan: protect the workingset on anonymous LRU

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Date:   Thu, 19 Mar 2020 13:01:24 +0900
From:   Joonsoo Kim <js1304@...il.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>, kernel-team@....com,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v3 2/9] mm/vmscan: protect the workingset on anonymous LRU

2020년 3월 19일 (목) 오전 2:52, Johannes Weiner <hannes@...xchg.org>님이 작성:
>
> On Tue, Mar 17, 2020 at 02:41:50PM +0900, js1304@...il.com wrote:
> > From: Joonsoo Kim <iamjoonsoo.kim@....com>
> >
> > In current implementation, newly created or swap-in anonymous page
> > is started on active list. Growing active list results in rebalancing
> > active/inactive list so old pages on active list are demoted to inactive
> > list. Hence, the page on active list isn't protected at all.
> >
> > Following is an example of this situation.
> >
> > Assume that 50 hot pages on active list. Numbers denote the number of
> > pages on active/inactive list (active | inactive).
> >
> > 1. 50 hot pages on active list
> > 50(h) | 0
> >
> > 2. workload: 50 newly created (used-once) pages
> > 50(uo) | 50(h)
> >
> > 3. workload: another 50 newly created (used-once) pages
> > 50(uo) | 50(uo), swap-out 50(h)
> >
> > This patch tries to fix this issue.
> > Like as file LRU, newly created or swap-in anonymous pages will be
> > inserted to the inactive list. They are promoted to active list if
> > enough reference happens. This simple modification changes the above
> > example as following.
> >
> > 1. 50 hot pages on active list
> > 50(h) | 0
> >
> > 2. workload: 50 newly created (used-once) pages
> > 50(h) | 50(uo)
> >
> > 3. workload: another 50 newly created (used-once) pages
> > 50(h) | 50(uo), swap-out 50(uo)
> >
> > As you can see, hot pages on active list would be protected.
> >
> > Note that, this implementation has a drawback that the page cannot
> > be promoted and will be swapped-out if re-access interval is greater than
> > the size of inactive list but less than the size of total(active+inactive).
> > To solve this potential issue, following patch will apply workingset
> > detection that is applied to file LRU some day before.
> >
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
>
> Acked-by: Johannes Weiner <hannes@...xchg.org>
>
> > -void lru_cache_add_active_or_unevictable(struct page *page,
> > +void lru_cache_add_inactive_or_unevictable(struct page *page,
> >                                        struct vm_area_struct *vma)
> >  {
> > +     bool evictable;
> > +
> >       VM_BUG_ON_PAGE(PageLRU(page), page);
> >
> > -     if (likely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) != VM_LOCKED))
> > -             SetPageActive(page);
> > -     else if (!TestSetPageMlocked(page)) {
> > +     evictable = (vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) != VM_LOCKED;
> > +     if (!evictable && !TestSetPageMlocked(page)) {
>
> Minor point, but in case there is a v4: `unevictable` instead of
> !evictable would be a bit easier to read, match the function name,
> PageUnevictable etc.

Okay. Looks like v4 is needed so I will change it as you said.

Thanks.