linux-kernel - Re: [RFC] propagate gfp_t to page table alloc functions

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Date:	Tue, 24 Apr 2012 19:55:43 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Hugh Dickins <hughd@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC] propagate gfp_t to page table alloc functions

On Tue, Apr 24, 2012 at 7:49 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> (2012/04/25 6:30), Andrew Morton wrote:
>
>> On Tue, 24 Apr 2012 17:48:29 +1000
>> Nick Piggin <npiggin@...il.com> wrote:
>>
>>>> Hmm, there are several places to use GFP_NOIO and GFP_NOFS even, GFP_ATOMIC.
>>>> I believe it's not trivial now.
>>>
>>> They're all buggy then. Unfortunately not through any real fault of their own.
>>
>> There are gruesome problems in block/blk-throttle.c (thread "mempool,
>> percpu, blkcg: fix percpu stat allocation and remove stats_lock").  It
>> wants to do an alloc_percpu()->vmalloc() from the IO submission path,
>> under GFP_NOIO.
>>
>> Changing vmalloc() to take a gfp_t does make lots of sense, although I
>> worry a bit about making vmalloc() easier to use!
>>
>> I do wonder whether the whole scheme of explicitly passing a gfp_t was
>> a mistake and that the allocation context should be part of the task
>> context.  ie: pass the allocation mode via *current.
>
> yes...that's very interesting.

I think GFP_ATOMIC is used non task context too. ;-)
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