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From:   Joonsoo Kim <js1304@gmail.com>
Date:   Thu, 19 Mar 2020 13:01:24 +0900
Message-ID: <CAAmzW4NE30PX27K55o_5kZuXsqM6jTeshd0tEzq+BLRK5kxJXw@mail.gmail.com>
Subject: Re: [PATCH v3 2/9] mm/vmscan: protect the workingset on anonymous LRU
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Michal Hocko <mhocko@kernel.org>,
        Hugh Dickins <hughd@google.com>,
        Minchan Kim <minchan@kernel.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Mel Gorman <mgorman@techsingularity.net>, kernel-team@lge.com,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>
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2020=EB=85=84 3=EC=9B=94 19=EC=9D=BC (=EB=AA=A9) =EC=98=A4=EC=A0=84 2:52, J=
ohannes Weiner <hannes@cmpxchg.org>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
>
> On Tue, Mar 17, 2020 at 02:41:50PM +0900, js1304@gmail.com wrote:
> > From: Joonsoo Kim <iamjoonsoo.kim@lge.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 inactiv=
e
> > 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 th=
an
> > the size of inactive list but less than the size of total(active+inacti=
ve).
> > 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@lge.com>
>
> Acked-by: Johannes Weiner <hannes@cmpxchg.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)) !=3D VM_LOC=
KED))
> > -             SetPageActive(page);
> > -     else if (!TestSetPageMlocked(page)) {
> > +     evictable =3D (vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) !=3D 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.