Re: [PATCH v2] mm/page_alloc: apply per-task GFP context in bulk allocator

[Vlastimil Babka (SUSE)]

On 9/14/26 10:04, Qiqi Liu wrote:
> alloc_pages_bulk_noprof() does not call current_gfp_context(), so
> per-task scoped allocation constraints (PF_MEMALLOC_NOIO,
> PF_MEMALLOC_NOFS, PF_MEMALLOC_PIN) are not applied on the bulk fast
> path.
> 
> The most direct consequence is PF_MEMALLOC_PIN: without clearing

I'd say ignoring PF_MEMALLOC_NOFS/PF_MEMALLOC_NOIO also can have a direct
consequence?

Let's replace the line above with:

By ignoring PF_MEMALLOC_NOIO and PF_MEMALLOC_NOFS, the allocation can
theoretically result in a deadlock.

Ignoring PF_MEMALLOC_PIN also has consequences: without clearing ...

> __GFP_MOVABLE, prepare_alloc_pages() selects MIGRATE_MOVABLE for
> the PCP list, and a task with PF_MEMALLOC_PIN set receives movable
> pages from the bulk allocator.  Once pinned, these pages can no
> longer be migrated but remain in MOVABLE pageblocks, violating the
> mobility contract.  This can increase fragmentation and interfere
> with compaction or contiguous-memory allocations, eventually
> surfacing as higher allocation latency or allocation failures under
> memory pressure.
> 
> Found via review of the bulk allocation tracepoint hooks [1].
> 
> [1] https://lore.kernel.org/all/20260907120949.418450-1-liuqiqi@xxxxxxxxxx/
> Link: https://sashiko.dev/#/patchset/20260907120949.418450-1-liuqiqi%40kylinos.cn
> Fixes: 387ba26fb1cb ("mm/page_alloc: add a bulk page allocator")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Qiqi Liu <liuqiqi@xxxxxxxxxx>

LGTM.

Reviewed-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>

> ---
>  mm/page_alloc.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 12fac9084c48..3be7288a1aa7 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5207,6 +5207,7 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
>  
>  	/* May set ALLOC_NOFRAGMENT, fragmentation will return 1 page. */
>  	gfp &= gfp_allowed_mask;
> +	gfp = current_gfp_context(gfp);
>  	if (!prepare_alloc_pages(gfp, 0, preferred_nid, nodemask, &ac, &gfp, &alloc_flags))
>  		goto out;
>