linux-kernel - Re: [PATCH 13/12] ksm: fix munlock during exit

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Date:	Wed, 26 Aug 2009 20:57:27 +0100 (BST)
From:	Hugh Dickins <hugh.dickins@...cali.co.uk>
To:	Andrea Arcangeli <aarcange@...hat.com>
cc:	Izik Eidus <ieidus@...hat.com>, Rik van Riel <riel@...hat.com>,
	Chris Wright <chrisw@...hat.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Justin M. Forbes" <jmforbes@...uxtx.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 13/12] ksm: fix munlock during exit_mmap deadlock

On Wed, 26 Aug 2009, Andrea Arcangeli wrote:
> 
> All is left to address is to teach page_alloc.c that the mm is going
> away in a second patch. That might also help when it's aio triggering
> gup page allocations or other kernel threads with use_mm just like ksm
> and the oom killer selected those "mm" for release.
> 
> Having ksm using use_mm before triggering the handle_mm_fault (so
> tsk->mm points to the mm of the task) and adding a MMF_MEMDIE to
> mm->flags checked by page_alloc would work just fine and should solve
> the double task killed... but then I'm unsure.. this is just the first
> idea I had.

Yes, I began to have thoughts along those lines too as I was writing
my reply.  It is a different angle on the problem, I hadn't looked at
it that way before, and it does seem worth pursuing.  MMF_MEMDIE, yes,
that might be useful.  But KSM_RUN_UNMERGE wouldn't be able to use_mm
since it's coming from a normal user process - perhaps it should be a
kill-me-first like swapoff via PF_SWAPOFF.

Hugh
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