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

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Date:   Fri, 15 Jan 2021 16:47:37 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     huang ying <huang.ying.caritas@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        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

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> 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...

OK.  I will start from a simpler version and only use a pagevec if
there's measurable difference.

Best Regards,
Huang, Ying