linux-kernel - Re: exit_mmap() BUG_ON triggering since 3.1

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Message-ID: <20120216214245.GD23585@redhat.com>
Date:	Thu, 16 Feb 2012 22:42:45 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Dave Jones <davej@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kernel-team@...oraproject.org
Subject: Re: exit_mmap() BUG_ON triggering since 3.1

On Thu, Feb 16, 2012 at 01:53:04AM -0800, Hugh Dickins wrote:
> Yes (and I think less troublesome than most BUGs, coming at exit
> while not holding locks; though we could well make it a WARN_ON,
> I don't think that existed back in the day).

A WARN_ON would be fine with me, go ahead if you prefer it... only
risk would be to go unnoticed or be underestimated. I am ok with the
BUG_ON too (even if this time it triggered false positives... sigh).

> Acked-by: Hugh Dickins <hughd@...gle.com>

Thanks for the quick review!

> In looking into the bug, it had actually bothered me a little that you
> were setting aside those pages, yet not counting them into nr_ptes;
> though the only thing that cares is oom_kill.c, and the count of pages
> in each hugepage can only dwarf the count in nr_ptes (whereas, without
> hugepages, it's possible to populate very sparsely and nr_ptes become
> significant).

Agreed, it's not significant either ways.

Running my two primary systems with this applied for half a day and no
problem so far so it should be good for -mm at least.
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