linux-kernel - Re: [PATCH v4 1/4] mm: Don't skip swap entry even if zap

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Message-Id: <20220216185455.c5af4f44f90b103971f34e1f@linux-foundation.org>
Date:   Wed, 16 Feb 2022 18:54:55 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Matthew Wilcox <willy@...radead.org>,
        Yang Shi <shy828301@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Alistair Popple <apopple@...dia.com>,
        David Hildenbrand <david@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v4 1/4] mm: Don't skip swap entry even if zap_details
 specified

On Wed, 16 Feb 2022 17:48:07 +0800 Peter Xu <peterx@...hat.com> wrote:

> The "details" pointer shouldn't be the token to decide whether we should skip
> swap entries.  For example, when the user specified details->zap_mapping==NULL,
> it means the user wants to zap all the pages (including COWed pages), then we
> need to look into swap entries because there can be private COWed pages that
> was swapped out.

I assume "user" here means "caller".

> Skipping some swap entries when details is non-NULL may lead to wrongly leaving
> some of the swap entries while we should have zapped them.
> 
> A reproducer of the problem:
> 
> ...
>
> The issue seems to exist starting from the initial commit of git.

I'll add cc:stable to this one, thanks.