linux-kernel - Re: [PATCH v2] mm/hugetlb: Restore failed global reservations to subpool

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Message-Id: <20260121094754.8a30b7f7fcff34f579883e40@linux-foundation.org>
Date: Wed, 21 Jan 2026 09:47:54 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Joshua Hahn <joshua.hahnjy@...il.com>
Cc: David Hildenbrand <david@...nel.org>, Muchun Song
 <muchun.song@...ux.dev>, Oscar Salvador <osalvador@...e.de>, Wupeng Ma
 <mawupeng1@...wei.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 stable@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH v2] mm/hugetlb: Restore failed global reservations to
 subpool

On Fri, 16 Jan 2026 15:40:36 -0500 Joshua Hahn <joshua.hahnjy@...il.com> wrote:

> Commit a833a693a490 ("mm: hugetlb: fix incorrect fallback for subpool")
> fixed an underflow error for hstate->resv_huge_pages caused by
> incorrectly attributing globally requested pages to the subpool's
> reservation.
> 
> Unfortunately, this fix also introduced the opposite problem, which would
> leave spool->used_hpages elevated if the globally requested pages could
> not be acquired. This is because while a subpool's reserve pages only
> accounts for what is requested and allocated from the subpool, its
> "used" counter keeps track of what is consumed in total, both from the
> subpool and globally. Thus, we need to adjust spool->used_hpages in the
> other direction, and make sure that globally requested pages are
> uncharged from the subpool's used counter.
> 
> ...
> 
> Fixes: a833a693a490 ("mm: hugetlb: fix incorrect fallback for subpool")
> Signed-off-by: Joshua Hahn <joshua.hahnjy@...il.com>
> Cc: stable@...r.kernel.org

This (simple, cc:stable) patch presently has no reviews, if someone
could please be so kind.

> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6713,6 +6713,15 @@ long hugetlb_reserve_pages(struct inode *inode,
>  		 */
>  		hugetlb_acct_memory(h, -gbl_resv);
>  	}
> +	/* Restore used_hpages for pages that failed global reservation */
> +	if (gbl_reserve && spool) {
> +		unsigned long flags;
> +
> +		spin_lock_irqsave(&spool->lock, flags);
> +		if (spool->max_hpages != -1)
> +			spool->used_hpages -= gbl_reserve;
> +		unlock_or_release_subpool(spool, flags);
> +	}
>  out_uncharge_cgroup:
>  	hugetlb_cgroup_uncharge_cgroup_rsvd(hstate_index(h),
>  					    chg * pages_per_huge_page(h), h_cg);
>