linux-kernel - Re: [PATCH] mm: Fix the pgtable leak

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Date:   Thu, 14 Feb 2019 16:23:52 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Liu Bo <bo.liu@...ux.alibaba.com>, stable@...r.kernel.org
Subject: Re: [PATCH] mm: Fix the pgtable leak

On Wed, Feb 13, 2019 at 02:36:24PM +0100, Greg KH wrote:
> On Wed, Feb 13, 2019 at 08:29:00PM +0900, Minchan Kim wrote:
> > [1] was backported to v4.9 stable tree but it introduces pgtable
> > memory leak because with fault retrial, preallocated pagetable
> > could be leaked in second iteration.
> > To fix the problem, this patch backport [2].
> > 
> > [1] 5cf3e5ff95876, mm, memcg: fix reclaim deadlock with writeback
> 
> This is really commit 63f3655f9501 ("mm, memcg: fix reclaim deadlock
> with writeback") which was in 4.9.152, 4.14.94, 4.19.16, and 4.20.3 as
> well as 5.0-rc2.

Since 4.10, we has [2] so it should be okay other (tree > 4.10)

> 
> > [2] b0b9b3df27d10, mm: stop leaking PageTables
> 
> This commit was in 4.10, so I am guessing that this really is just a
> backport of that commit?

Yub.

> 
> If so, it's not the full backport, why not take the whole thing?  Why
> only cherry-pick one chunk of it?  Why do we not need the other parts?

Because [2] actually aims for fixing [3] which was introduced at 4.10.
Since then, [1] relies on the chunk I sent. Thus we don't need other part
for 4.9.

[3] 953c66c2b22a ("mm: THP page cache support for ppc64")

Thanks.