linux-kernel - Re: [PATCH] mm/workingset: don't count as refault (file/anon) if refault distance is too long

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Message-Id: <20210914203908.bdb8fa924dce80e15f149457@linux-foundation.org>
Date:   Tue, 14 Sep 2021 20:39:08 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Yongmei Xie <yongmeixie@...mail.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        hannes@...xchg.org
Subject: Re: [PATCH] mm/workingset: don't count as refault (file/anon) if
 refault distance is too long

On Sun, 12 Sep 2021 19:54:47 +0800 Yongmei Xie <yongmeixie@...mail.com> wrote:

> The current implementation count all the pages which have shadow entry in radix tree as
> the event of refault (page or anon). That means all the pages which have ever been
> cached in lru are counted as refault. But I think it's not 100% percent correct.
> 
> Because usually inode has much longer life cycle than the pages belonging to it.
> So if the inode was accessed from time to time, then it won't be reclaimed unless much
> severe memory pressure happens.
> 
> Then if page was reclaimed several days ago, when it's accessed again, it will be marked as
> refault event. Then page was reclaimed an hour ago, when it's accessed again, it will be
> marked as refault event as well. From the refault metric alone, I cannot tell whether the
> previous reclaim process has evicted some useful pages. That makes things worse in situation
> of proactive reclaim. We's like to known whehter the previous policy reclaim too much
> meaningful data other than working set transition. So we'd like see the refault rate, but it
> includes all the historical reclaim.
> 
> >From my point of view, if the refaut distance is larger than file cache size, we don't
> have to count it refault at all. Because it's too long to be memorized down.

Thanks.

Do you have any runtime testing results which demonstrate a benefit?