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Message-ID: <YnrcxjN9SRgHS05s@google.com>
Date: Tue, 10 May 2022 14:44:38 -0700
From: Minchan Kim <minchan@...nel.org>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
linux-mm <linux-mm@...ck.org>,
Suren Baghdasaryan <surenb@...gle.com>,
Michal Hocko <mhocko@...e.com>,
John Dias <joaodias@...gle.com>,
Tim Murray <timmurray@...gle.com>,
Matthew Wilcox <willy@...radead.org>,
Vladimir Davydov <vdavydov.dev@...il.com>,
Martin Liu <liumartin@...gle.com>
Subject: Re: [PATCH v3] mm: don't be stuck to rmap lock on reclaim path
On Tue, May 10, 2022 at 02:16:07PM -0400, Johannes Weiner wrote:
> Hi Minchan,
>
> The patch looks reasonable to me, but one thing stands out:
>
> On Tue, May 10, 2022 at 10:11:00AM -0700, Minchan Kim wrote:
> > @@ -1391,6 +1391,10 @@ static enum page_references folio_check_references(struct folio *folio,
> > if (vm_flags & VM_LOCKED)
> > return PAGEREF_ACTIVATE;
> >
> > + /* page_referenced didn't work due to lock contention */
> > + if (referenced_ptes == -1)
> > + return PAGEREF_KEEP;
> > +
> > if (referenced_ptes) {
> > /*
> > * All mapped folios start out with page table
>
> This means contended inactive pages get rotated.
>
> > @@ -2492,7 +2496,7 @@ static void shrink_active_list(unsigned long nr_to_scan,
> > }
> >
> > if (folio_referenced(folio, 0, sc->target_mem_cgroup,
> > - &vm_flags)) {
> > + &vm_flags) > 0) {
> > /*
> > * Identify referenced, file-backed active pages and
> > * give them one more trip around the active list. So
>
> This means contended active pages do NOT get rotated.
>
> It's a bit of an arbitrary choice what to do with reclaim candidates
> for which you can get no reference information, but staying consistent
> is likely a good idea. My preference would be to just rotate contended
> pages throughout rather than risk dropping the workingset on the floor.
>
> /* Referenced or rmap lock contention: rotate */
> if (folio_referenced() != 0) {
> ...
>
> What do you think?
Sure, it's good start before adding more heuristic later.
Thanks for the review. I will post v4.
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