From: Michal Hocko <mhocko@suse.com>
To: Rik van Riel <riel@surriel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, stable@kernel.org,
Chris Down <chris@chrisdown.name>,
Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH] mm,vmscan: fix divide by zero in get_scan_count
Date: Mon, 30 Aug 2021 15:41:19 +0200 [thread overview]
Message-ID: <YSzf/3A6b0R3kR5v@dhcp22.suse.cz> (raw)
In-Reply-To: <d77b816458f9df3839345f0ee0144b797ec176be.camel@surriel.com>
On Mon 30-08-21 09:24:22, Rik van Riel wrote:
> On Mon, 2021-08-30 at 13:33 +0200, Michal Hocko wrote:
[...]
> > I must be missing something but how can cgroup_size be ever 0 when it
> > is
> > max(cgroup_size, protection) and protection != 0?
>
> Going into the condition we use if (low || min), where
> it is possible for low > 0 && min == 0.
>
> Inside the conditional, we can end up testing against
> min.
Dang, I was looking at the tree without f56ce412a59d7 applied. My bad!
Personally I would consider the following slightly easier to follow
scan = lruvec_size - lruvec_size * protection /
max(cgroup_size, 1);
The code is quite tricky already and if you asked me what kind of effect
cgroup_size + 1 have there I would just shrug shoulders...
Anyway your fix will prevent the reported problem and I cannot see any
obvious problem with it either so
Acked-by: Michal Hocko <mhocko@suse.com>
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2021-08-30 13:41 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-27 2:01 [PATCH] mm,vmscan: fix divide by zero in get_scan_count Rik van Riel
2021-08-27 16:28 ` Roman Gushchin
2021-08-30 11:33 ` Michal Hocko
2021-08-30 13:24 ` Rik van Riel
2021-08-30 13:41 ` Michal Hocko [this message]
2021-08-30 20:48 ` Johannes Weiner
2021-08-31 9:59 ` Michal Hocko
2021-08-31 15:48 ` Rik van Riel
2021-09-01 19:40 ` Johannes Weiner
2021-08-31 12:58 ` Chris Down
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