Re: [PATCH v2 09/10] mm: Skip might_alloc() warnings when PF_MEMALLOC is set

[Michal Hocko <mhocko@suse.com>]

On Mon 15-09-25 15:40:39, Uladzislau Rezki wrote:
> might_alloc() catches invalid blocking allocations in contexts
> where sleeping is not allowed.
> 
> However when PF_MEMALLOC is set, the page allocator already skips
> reclaim and other blocking paths. In such cases, a blocking gfp_mask
> does not actually lead to blocking, so triggering might_alloc() splats
> is misleading.
> 
> Adjust might_alloc() to skip warnings when the current task has
> PF_MEMALLOC set, matching the allocator's actual blocking behaviour.
> 
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

I would probably just bail out early for PF_MEMALLOC to not meddle with
might_sleep_if condition as it seems to read better but I do not insist.
Acked-by: Michal Hocko <mhocko@suse.com>
Thanks

> ---
>  include/linux/sched/mm.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index 2201da0afecc..dc2d3cab32ef 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -318,7 +318,8 @@ static inline void might_alloc(gfp_t gfp_mask)
>  	fs_reclaim_acquire(gfp_mask);
>  	fs_reclaim_release(gfp_mask);
>  
> -	might_sleep_if(gfpflags_allow_blocking(gfp_mask));
> +	might_sleep_if(gfpflags_allow_blocking(gfp_mask) &&
> +		!(current->flags & PF_MEMALLOC));
>  }
>  
>  /**
> -- 
> 2.47.3

-- 
Michal Hocko
SUSE Labs