linux-kernel - Re: [PATCH] mm: reduce spinlock contention in release

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Date:   Thu, 25 Nov 2021 11:13:54 +0800
From:   Hao Lee <haolee.swjtu@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Linux MM <linux-mm@...ck.org>,
        Johannes Weiner <hannes@...xchg.org>, mhocko@...nel.org,
        vdavydov.dev@...il.com, Shakeel Butt <shakeelb@...gle.com>,
        cgroups@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: reduce spinlock contention in release_pages()

On Wed, Nov 24, 2021 at 11:58 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Wed, Nov 24, 2021 at 03:19:15PM +0000, Hao Lee wrote:
> > When several tasks are terminated simultaneously, lots of pages will be
> > released, which can cause severe spinlock contention. Other tasks which
> > are running on the same core will be seriously affected. We can yield
> > cpu to fix this problem.
>
> The realtime people will eat you alive for this suggestion.

Thanks for pointing out this.

>
> > +++ b/mm/swap.c
> > @@ -960,8 +960,14 @@ void release_pages(struct page **pages, int nr)
> >               if (PageLRU(page)) {
> >                       struct lruvec *prev_lruvec = lruvec;
> >
> > -                     lruvec = folio_lruvec_relock_irqsave(folio, lruvec,
> > +retry:
> > +                     lruvec = folio_lruvec_tryrelock_irqsave(folio, lruvec,
> >                                                                       &flags);
> > +                     if (!lruvec) {
> > +                             cond_resched();
> > +                             goto retry;
> > +                     }
> > +
> >                       if (prev_lruvec != lruvec)