Re: [PATCH] mm,page_alloc: apply gfp_allowed_mask before the first allocation attempt.

[Vlastimil Babka <vbabka@suse.cz>]

On 09/01/2017 05:16 PM, Tetsuo Handa wrote:
> Michal Hocko wrote:
>> On Fri 01-09-17 23:11:31, Tetsuo Handa wrote:
>>> We are by error initializing alloc_flags before gfp_allowed_mask is
>>> applied. Apply gfp_allowed_mask before initializing alloc_flags so that
>>> the first allocation attempt uses correct flags.
>>
>> It would be worth noting that this will not matter in most cases,
>> actually when only the node reclaim is enabled we can misbehave because
>> NOFS request for PM paths would be ignored.

Hmm don't we have the same problem with the god-damned node reclaim by
applying current_gfp_context() also only after the first attempt? But
that would be present since 21caf2fc1931b.
Hm, actually no, because reclaim calls current_gfp_context() by itself.
Good. Maybe reclaim should also do the gfp_allowed_mask filtering? I
wonder how safe the pm_restrict_gfp_mask() update is when an allocation
is already looping in __alloc_pages_slowpath()...
What exactly are your ideas to get rid of gfp_allowed_mask, Michal?

>>> Fixes: 9cd7555875bb09da ("mm, page_alloc: split alloc_pages_nodemask()")
>>
>> AFAICS this patch hasn't changed the logic and it was broken since
>> 83d4ca8148fd ("mm, page_alloc: move __GFP_HARDWALL modifications out of
>> the fastpath")
> 
> Indeed. Updated patch follows.
> 
>>
>>> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>>> Cc: Mel Gorman <mgorman@techsingularity.net>
>>> Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
>>> Cc: Vlastimil Babka <vbabka@suse.cz>
>>> Cc: Jesper Dangaard Brouer <brouer@redhat.com>
>>
>> Other than that this looks correct to me. 
>> Acked-by: Michal Hocko <mhocko@suse.com>
>>
>> I wish we can finally get rid of gfp_allowed_mask. I have it on my todo
>> list but never got to it.
>>
>> Thanks!
>>
> ----------
>>From b454863bea884158a25460aa29a26c5feb16fe94 Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Date: Fri, 1 Sep 2017 23:11:31 +0900
> Subject: [PATCH v2] mm,page_alloc: apply gfp_allowed_mask before the first
>  allocation attempt.
> 
> We are by error initializing alloc_flags before gfp_allowed_mask is
> applied. This could cause problems after pm_restrict_gfp_mask() is
> called during suspend operation. Apply gfp_allowed_mask before
> initializing alloc_flags so that the first allocation attempt uses
> correct flags.
> 
> Fixes: 83d4ca8148fd9092 ("mm, page_alloc: move __GFP_HARDWALL modifications out of the fastpath")
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Jesper Dangaard Brouer <brouer@redhat.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  mm/page_alloc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6dbc49e..a123dee 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4179,10 +4179,11 @@ struct page *
>  {
>  	struct page *page;
>  	unsigned int alloc_flags = ALLOC_WMARK_LOW;
> -	gfp_t alloc_mask = gfp_mask; /* The gfp_t that was actually used for allocation */
> +	gfp_t alloc_mask; /* The gfp_t that was actually used for allocation */
>  	struct alloc_context ac = { };
>  
>  	gfp_mask &= gfp_allowed_mask;
> +	alloc_mask = gfp_mask;
>  	if (!prepare_alloc_pages(gfp_mask, order, preferred_nid, nodemask, &ac, &alloc_mask, &alloc_flags))
>  		return NULL;
>  
> 

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>