Re: [PATCH v5 03/36] mm/page_alloc: let the bulk and folio allocators carry alloc_flags

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The newly added `alloc_flags` parameter is ignored during the bulk allocation fastpath when calling `prep_new_page`.
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--- Patch [3]: [PATCH v5 03/36] mm/page_alloc: let the bulk and folio allocators carry alloc_flags ---
commit 00718b17ea28c0a7382f9831d41a8a45df59e496
Author: Gregory Price <[email protected]>

mm/page_alloc: let the bulk and folio allocators carry alloc_flags

This commit threads the alloc_flags parameter through the bulk and folio
allocators to allow callers to select specific allocator behavior. It updates
__alloc_pages_bulk_noprof and __folio_alloc_noprof to accept and pass these
flags internally.

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c

[ ... ]

> @@ -5238,11 +5239,19 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
>  	return nr_populated;
>  
>  failed:
> -	page = __alloc_pages_noprof(gfp, 0, preferred_nid, nodemask, ALLOC_DEFAULT);
> +	page = __alloc_pages_noprof(gfp, 0, preferred_nid, nodemask, alloc_flags);
>  	if (page)
>  		page_array[nr_populated++] = page;
>  	goto out;
>  }

[Severity: Medium]
Will the fast path ignore the caller's new alloc_flags parameter?

In the slow path fallback above, the code correctly passes the new alloc_flags
parameter to __alloc_pages_noprof(). However, in the fast path batch
allocation loop just above this hunk, the pages are still initialized with a
hardcoded ALLOC_DEFAULT:

__alloc_pages_bulk_noprof() {
    ...
    while (nr_populated < nr_pages) {
        ...
        page = __rmqueue_pcplist(...);
        ...
        prep_new_page(page, 0, gfp, ALLOC_DEFAULT);
        set_page_refcounted(page);
        page_array[nr_populated++] = page;
    }
}

If a caller passes custom alloc_flags to __alloc_pages_bulk_noprof(), it
appears the flags will be dropped by the fast path but honored by the slow
path, leading to inconsistent allocator behavior.

Should prep_new_page() in the fast path loop be updated to use the provided
alloc_flags instead of ALLOC_DEFAULT?

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Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=3