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Date: Thu, 29 Feb 2024 13:05:02 -0700
From: Greg Edwards <gedwards@ddn.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>, Andrew Morton <akpm@linux-foundation.org>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Hugh Dickins <hughd@google.com>, linux-mm@kvack.org,
	linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org,
	qemu-devel@nongnu.org
Subject: Re: [PATCH] block: Remove special-casing of compound pages
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On Thu, Feb 29, 2024 at 07:37:11PM +0000, Matthew Wilcox wrote:
> 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.
>
> 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.

This does appear to fix it.  Thank you!

I'll do some more testing on it today, then add a Tested-by: tag if it
holds up.

Greg