linux-kernel - Re: [PATCH] mm,hugetlb: Allocate frozen pages in alloc_buddy_hugetlb

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Message-ID: <f0373427-b4e8-4612-b668-980d93febe26@redhat.com>
Date: Fri, 11 Apr 2025 15:44:31 +0200
From: David Hildenbrand <david@...hat.com>
To: Oscar Salvador <osalvador@...e.de>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Muchun Song <muchun.song@...ux.dev>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
 Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH] mm,hugetlb: Allocate frozen pages in
 alloc_buddy_hugetlb_folio

On 11.04.25 15:23, Oscar Salvador wrote:
> alloc_buddy_hugetlb_folio() allocates a rmappable folio, then strips the
> rmappable part and freezes it.
> We can simplify all that by allocating frozen pages directly.
> 
> Suggested-by: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> ---
>   mm/hugetlb.c | 17 +----------------
>   1 file changed, 1 insertion(+), 16 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index e3e6ac991b9c..83fa2b9f6fc4 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1950,7 +1950,6 @@ static struct folio *alloc_buddy_hugetlb_folio(struct hstate *h,
>   	int order = huge_page_order(h);
>   	struct folio *folio;
>   	bool alloc_try_hard = true;
> -	bool retry = true;
>   
>   	/*
>   	 * By default we always try hard to allocate the folio with
> @@ -1965,22 +1964,8 @@ static struct folio *alloc_buddy_hugetlb_folio(struct hstate *h,
>   		gfp_mask |= __GFP_RETRY_MAYFAIL;
>   	if (nid == NUMA_NO_NODE)
>   		nid = numa_mem_id();
> -retry:
> -	folio = __folio_alloc(gfp_mask, order, nid, nmask);
> -	/* Ensure hugetlb folio won't have large_rmappable flag set. */
> -	if (folio)
> -		folio_clear_large_rmappable(folio);
>   
> -	if (folio && !folio_ref_freeze(folio, 1)) {
> -		folio_put(folio);
> -		if (retry) {	/* retry once */
> -			retry = false;
> -			goto retry;
> -		}
> -		/* WOW!  twice in a row. */
> -		pr_warn("HugeTLB unexpected inflated folio ref count\n");
> -		folio = NULL;
> -	}
> +	folio = (struct folio *)__alloc_frozen_pages(gfp_mask, order, nid, nmask);
>   
>   	/*
>   	 * If we did not specify __GFP_RETRY_MAYFAIL, but still got a

I assume htlb_alloc_mask() will always include _GFP_COMP.

But semantically, it might be wrong: __folio_alloc() will in the memdesc 
world also make sure to allocate the memdesc, __alloc_frozen_pages() not.

Maybe one would want a __alloc_frozen_folio() .... @willy?

-- 
Cheers,

David / dhildenb