linux-kernel - Re: [RFC/PATCH v2] mm: Introduce GFP

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Date:	Fri, 08 May 2009 10:37:02 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
CC:	Christoph Lameter <cl@...ux.com>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, mingo@...e.hu,
	mel@....ul.ie, linux-kernel@...r.kernel.org, rientjes@...gle.com,
	xemul@...nvz.org
Subject: Re: [RFC/PATCH v2] mm: Introduce GFP_PANIC for non-failing allocations

Pekka Enberg wrote:
> On Fri, 2009-05-08 at 10:29 -0400, Christoph Lameter wrote:
>> On Fri, 8 May 2009, Pekka Enberg wrote:
>>
>>> On Fri, 8 May 2009, Pekka Enberg wrote:
>>>>> +#define GFP_PANIC	(__GFP_NOFAIL | __GFP_NORETRY | __GFP_NOMEMALLOC)
>>> On Fri, 2009-05-08 at 10:20 -0400, Christoph Lameter wrote:
>>>> So this means not retrying the allocation a couple of times? Not delving
>>>> into reserve pools? Such behavior is good for a allocation that causes a
>>>> panic if it fails?
>>> If you do GFP_KERNEL|GFP_PANIC, we will cond_resched() and retry if we
>>> made some progress. So yes, I think the behavior is good for early-boot
>>> call-sites that can't really fail anyway.
>> Better make sure that GFP_PANIC is only used during early boot then.
>>
>> If memory is low on boot (due to node hotplug or some such thing, powerpc
>> may do evil tricks here) then the panic may trigger after the patch.
>> We would have just delved into the reserves a bit before.
> 
> Nah, it's probably better to drop __GFP_NOMEMALLOC instead. Does this
> look better?
> 
> 			Pekka
> 
>>>From c91c70265545f2fcc727b4a0d37162b5aa0f5ecf Mon Sep 17 00:00:00 2001
> From: Cyrill Gorcunov <gorcunov@...nvz.org>
> Date: Fri, 8 May 2009 15:44:50 +0300
> Subject: [PATCH] mm: Introduce GFP_PANIC for non-failing allocations
> 
> This patch introduces a GFP_PANIC flag that can be used as an annotation
> that a call to kmalloc() or alloc_pages() is expected to never fail.
> This is useful in early boot code, for example.
> 
> To save one GFP flag bit, use a combination of __GFP_NOFAIL,
> __GFP_NOREPEAT, and __GFP_NOMEMALLOC to make sure we always end up in
> the "nopage" path of the page allocator if an allocation fails.
> 
> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> Signed-off-by: Pekka Enberg <penberg@...helsinki.fi>
> ---
>  include/linux/gfp.h |    1 +
>  mm/page_alloc.c     |    6 +++++-
>  2 files changed, 6 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 0bbc15f..b34e6e5 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -70,6 +70,7 @@ struct vm_area_struct;
>  #define GFP_HIGHUSER_MOVABLE	(__GFP_WAIT | __GFP_IO | __GFP_FS | \
>  				 __GFP_HARDWALL | __GFP_HIGHMEM | \
>  				 __GFP_MOVABLE)
> +#define GFP_PANIC	(__GFP_NOFAIL | __GFP_NORETRY)
>  
>  #ifdef CONFIG_NUMA
>  #define GFP_THISNODE	(__GFP_THISNODE | __GFP_NOWARN | __GFP_NORETRY)
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index e2f2699..de7f666 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1556,7 +1556,8 @@ nofail_alloc:
>  				zonelist, high_zoneidx, ALLOC_NO_WATERMARKS);
>  			if (page)
>  				goto got_pg;
> -			if (gfp_mask & __GFP_NOFAIL) {
> +			/* GFP_PANIC sets both flags */
> +			if ((gfp_mask & __GFP_NOFAIL) && !(gfp_mask & __GFP_NORETRY)) {
>  				congestion_wait(WRITE, HZ/50);

Do you mean ((gfp_mask & GFP_PANIC) == GFP_PANIC))  ?

> @@ -1670,6 +1671,9 @@ nopage:
>  		dump_stack();
>  		show_mem();
>  	}
> +	if (unlikely(gfp_mask & GFP_PANIC))
> +		panic("Out of memory: %s order: %d, gfp_mask:0x%x\n",
> +			p->comm, order, gfp_mask);

Ditto here.

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