linux-kernel - Re: [PATCH 1/5] mm: Add __GFP_NO_OOM

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Message-ID: <alpine.DEB.2.00.0905041253380.23036@chino.kir.corp.google.com>
Date:	Mon, 4 May 2009 13:02:30 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Wu Fengguang <fengguang.wu@...el.com>,
	linux-pm@...ts.linux-foundation.org,
	Andrew Morton <akpm@...ux-foundation.org>, pavel@....cz,
	torvalds@...ux-foundation.org, jens.axboe@...cle.com,
	alan-jenkins@...fmail.co.uk, linux-kernel@...r.kernel.org,
	kernel-testers@...r.kernel.org
Subject: Re: [PATCH 1/5] mm: Add __GFP_NO_OOM_KILL flag

On Mon, 4 May 2009, Rafael J. Wysocki wrote:

> Index: linux-2.6/mm/page_alloc.c
> ===================================================================
> --- linux-2.6.orig/mm/page_alloc.c
> +++ linux-2.6/mm/page_alloc.c
> @@ -1599,7 +1599,8 @@ nofail_alloc:
>  					zonelist, high_zoneidx, alloc_flags);
>  		if (page)
>  			goto got_pg;
> -	} else if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY)) {
> +	} else if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY)
> +			&& !(gfp_mask & __GFP_NO_OOM_KILL)) {
>  		if (!try_set_zone_oom(zonelist, gfp_mask)) {
>  			schedule_timeout_uninterruptible(1);
>  			goto restart;
> Index: linux-2.6/include/linux/gfp.h
> ===================================================================
> --- linux-2.6.orig/include/linux/gfp.h
> +++ linux-2.6/include/linux/gfp.h
> @@ -51,8 +51,9 @@ struct vm_area_struct;
>  #define __GFP_THISNODE	((__force gfp_t)0x40000u)/* No fallback, no policies */
>  #define __GFP_RECLAIMABLE ((__force gfp_t)0x80000u) /* Page is reclaimable */
>  #define __GFP_MOVABLE	((__force gfp_t)0x100000u)  /* Page is movable */
> +#define __GFP_NO_OOM_KILL ((__force gfp_t)0x200000u)  /* Don't invoke out_of_memory() */
>  
> -#define __GFP_BITS_SHIFT 21	/* Room for 21 __GFP_FOO bits */
> +#define __GFP_BITS_SHIFT 22	/* Number of __GFP_FOO bits */
>  #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
>  
>  /* This equals 0, but use constants in case they ever change */
> 

Yeah, that's much better, thanks.  There's currently concerns about adding 
a new gfp flag in another thread (__GFP_PANIC), though, so you might find 
some resistance in adding a flag with a very specific and limited use cae.

I think you might have better luck in doing

	struct zone *z;

	for_each_populated_zone(z)
		zone_set_flag(z, ZONE_OOM_LOCKED);
	
if all other tasks are really in D state at this point since oom killer 
serialization is done with try locks in the page allocator.  This is 
equivalent to __GFP_NO_OOM_KILL.
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