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

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Message-Id: <20260202183918.057dac34b3a1819328814fc9@linux-foundation.org>
Date: Mon, 2 Feb 2026 18:39:18 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Joshua Hahn <joshua.hahnjy@...il.com>, 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 Wed, 21 Jan 2026 09:47:54 -0800 Andrew Morton <akpm@...ux-foundation.org> wrote:

> 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.

Oh.

Joshua, it's unclear from the changelog - what are the userspace-visible
effects of the bug?