Re: [RFC/PATCH v2] mm: Introduce GFP_PANIC for non-failing allocations

[Rik van Riel]

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@xxxxxxxxxx>
> 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@xxxxxxxxxx>
> Signed-off-by: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
> ---
>  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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