linux-kernel - Re: [PATCH v2] vma remove the unneeded avc bound with non-CoWed folio

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Message-ID: <aba1cad3-ab23-4b42-8ce8-0ed662919c99@lucifer.local>
Date: Sat, 24 Aug 2024 19:04:11 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Zhiguo Jiang <justinjiang@...o.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, oe-lkp@...ts.linux.dev, lkp@...el.com,
        opensource.kernel@...o.com
Subject: Re: [PATCH v2] vma remove the unneeded avc bound with non-CoWed folio

On Sat, Aug 24, 2024 at 05:26:46PM GMT, Lorenzo Stoakes wrote:
> On Fri, Aug 23, 2024 at 11:02:06PM GMT, Zhiguo Jiang wrote:
> > After CoWed by do_wp_page, the vma established a new mapping relationship
> > with the CoWed folio instead of the non-CoWed folio. However, regarding
> > the situation where vma->anon_vma and the non-CoWed folio's anon_vma are
> > not same, the avc binding relationship between them will no longer be
> > needed, so it is issue for the avc binding relationship still existing
> > between them.
> >
> > This patch will remove the avc binding relationship between vma and the
> > non-CoWed folio's anon_vma, which each has their own independent
> > anon_vma. It can also alleviates rmap overhead simultaneously.
> >
> > Signed-off-by: Zhiguo Jiang <justinjiang@...o.com>
>
>
> NACK (until fixed). This is broken (see below).
>

[snip]

I enclose a patch that fixes the issue, but leaves a LOT still
broken/resolved/todo including locking of the reparented anon_vma (that'll
really need re-rooting too).

I still seriously doubt the value of this patch given the complexity risks,
but since I got bored and looked into this it's useful to examine something
that works, and which might be helpful to you in testing.

View attachment "0001-mm-fixup-orphan-avc-cleanup-logic.patch" of type "text/plain" (6111 bytes)