linux-kernel - Re: [PATCH] coredump_filter: add hugepage core dumping

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Date:	Fri, 29 Aug 2008 08:35:28 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Kawai Hidehiro <hidehiro.kawai.ez@...achi.com>,
	William Irwin <wli@...omorphy.com>,
	Adam Litke <agl@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] coredump_filter: add hugepage core dumping

Hi

> > I think VM_RESERVED default dumping bahavior is good,
> > then I'd like to add coredump_filter mask.
> > 
> > This patch doesn't change dafault behavior.
> 
> This seems very reasonable to me
> (though I've little use for coredumps or hugepages myself).

Thanks a lot.

> One caution though: how well does it behave when coredumping a large
> area of hugepages which have not actually been instantiated prior to
> the coredump?  We have that funny FOLL_ANON ZERO_PAGE code in
> follow_page() to avoid wasting memory on large uninstantiated anon
> areas, but hugepages won't go that way.  If the dump hangs waiting for
> memory to be freed, or OOMkills other processes, that wouldn't be good;
> whereas if hugepage reservations (I've not followed what happens with
> them) or whatever just make it skip when no more, that should be okay.

I think hugepage reservation pages always exist when hugepage COW happend.
Then, hugepage access never cause try_to_free_pages() nor OOM.

Adam, if I talk lie, please tell us truth.




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