linux-kernel - Re: [RFC][PATCH 3/4] filemap: implement filemap allocate post callback for page

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Message-ID: <ZUz+8nlEaRMU8QaO@casper.infradead.org>
Date:   Thu, 9 Nov 2023 15:46:58 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     jeff.xie@...ux.dev
Cc:     akpm@...ux-foundation.org, iamjoonsoo.kim@....com, vbabka@...e.cz,
        cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        roman.gushchin@...ux.dev, 42.hyeyoo@...il.com, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        chensong_2000@....cn, xiehuan09@...il.com
Subject: Re: [RFC][PATCH 3/4] filemap: implement filemap allocate post
 callback for page_owner

On Thu, Nov 09, 2023 at 03:43:10PM +0000, jeff.xie@...ux.dev wrote:
> November 9, 2023 at 10:09 PM, "Matthew Wilcox" <willy@...radead.org> wrote:
> > Why not just walk the rmap directly to find out where it's mapped in
> > any process instead of the one which allocated it?
> 
> Since the page_owner's result only shows which PID allocated this page, we only need to obtain the address space of the corresponding process for that PID.

But that's probably uninteresting.  Consider, eg, a page from libc.
That's going to be mapped by hundreds or even thousands of processes.
And the one which originally allocated it may well have exited by this
point; files often live long past the process that first reads them.