linux-kernel - Re: [PATCH] mm: Free unused swap cache page in write protection fault handler

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Date:   Wed, 13 Jan 2021 13:09:31 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     huang ying <huang.ying.caritas@...il.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Huang Ying <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Xu <peterx@...hat.com>, Hugh Dickins <hughd@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...riel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Tim Chen <tim.c.chen@...el.com>
Subject: Re: [PATCH] mm: Free unused swap cache page in write protection fault handler

On Tue, Jan 12, 2021 at 9:24 PM huang ying <huang.ying.caritas@...il.com> wrote:
> >
> > Couldn't we just move it to the tail of the LRU list so it's reclaimed
> > first?  Or is locking going to be a problem here?
>
> Yes.  That's a way to reduce the disturbance to the page reclaiming.
> For LRU lock contention, is it sufficient to use another pagevec?

I wonder if this is really worth it. I'd like to see numbers.

Because in probably 99%+ of all cases, that LRU dance is only going to
hurt and add extra locking overhead and dirty caches.

So I'd like to see some numbers that it actually helps measurably in
whatever paging-heavy case...

            Linus