linux-kernel - Re: [PATCH] block: Remove special-casing of compound pages

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Date: Thu, 29 Feb 2024 19:37:11 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Greg Edwards <gedwards@....com>
Cc: Jens Axboe <axboe@...nel.dk>, Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
	linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	qemu-devel@...gnu.org
Subject: Re: [PATCH] block: Remove special-casing of compound pages

On Thu, Feb 29, 2024 at 11:25:13AM -0700, Greg Edwards wrote:
> > [1/1] block: Remove special-casing of compound pages
> >       commit: 1b151e2435fc3a9b10c8946c6aebe9f3e1938c55
> 
> This commit results in a change of behavior for QEMU VMs backed by hugepages
> that open their VM disk image file with O_DIRECT (QEMU cache=none or
> cache.direct=on options).  When the VM shuts down and the QEMU process exits,
> one or two hugepages may fail to free correctly.  It appears to be a race, as
> it doesn't happen every time.

Hi Greg,

By sheer coincidence the very next email after this one was:

https://lore.kernel.org/linux-mm/86e592a9-98d4-4cff-a646-0c0084328356@cybernetics.com/T/#u

Can you try Tony's patch and see if it fixes your problem?
I haven't even begun to analyse either your email or his patch,
but there's a strong likelihood that they're the same thing.