__vmalloc()/kvmalloc() and no-block support(v3)

[PATCH v3 08/10] mm: Skip might_alloc() warnings when PF_MEMALLOC is set

Posted by Uladzislau Rezki (Sony) 4 months, 1 week ago

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.

Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 include/linux/sched/mm.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 0232d983b715..a74582aed747 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -318,6 +318,9 @@ static inline void might_alloc(gfp_t gfp_mask)
 	fs_reclaim_acquire(gfp_mask);
 	fs_reclaim_release(gfp_mask);
 
+	if (current->flags & PF_MEMALLOC)
+		return;
+
 	might_sleep_if(gfpflags_allow_blocking(gfp_mask));
 }
 
-- 
2.47.3

Re: [PATCH v3 08/10] mm: Skip might_alloc() warnings when PF_MEMALLOC is set

Posted by Baoquan He 4 months, 1 week ago

On 10/01/25 at 09:26pm, Uladzislau Rezki (Sony) 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.
> 
> Acked-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> ---
>  include/linux/sched/mm.h | 3 +++
>  1 file changed, 3 insertions(+)

Reviewed-by: Baoquan He <bhe@redhat.com>

> 
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index 0232d983b715..a74582aed747 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -318,6 +318,9 @@ static inline void might_alloc(gfp_t gfp_mask)
>  	fs_reclaim_acquire(gfp_mask);
>  	fs_reclaim_release(gfp_mask);
>  
> +	if (current->flags & PF_MEMALLOC)
> +		return;
> +
>  	might_sleep_if(gfpflags_allow_blocking(gfp_mask));
>  }
>  
> -- 
> 2.47.3
>