linux-kernel - Re: [PATCH] iomap: use largest_zero_folio() in iomap_dio

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Message-ID: <4b225908-f788-413b-ba07-57a0d6012145@igalia.com>
Date: Mon, 18 Aug 2025 11:12:58 -0300
From: André Almeida <andrealmeid@...lia.com>
To: Christoph Hellwig <hch@...radead.org>,
 Christian Brauner <brauner@...nel.org>
Cc: "Darrick J . Wong" <djwong@...nel.org>,
 "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>,
 linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 mcgrof@...nel.org, gost.dev@...sung.com, linux-xfs@...r.kernel.org,
 Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH] iomap: use largest_zero_folio() in iomap_dio_zero()

Em 18/08/2025 01:41, Christoph Hellwig escreveu:
> On Fri, Aug 15, 2025 at 04:02:58PM +0200, Christian Brauner wrote:
>> On Thu, 14 Aug 2025 16:21:37 +0200, Pankaj Raghav (Samsung) wrote:
>>> iomap_dio_zero() uses a custom allocated memory of zeroes for padding
>>> zeroes. This was a temporary solution until there was a way to request a
>>> zero folio that was greater than the PAGE_SIZE.
>>>
>>> Use largest_zero_folio() function instead of using the custom allocated
>>> memory of zeroes. There is no guarantee from largest_zero_folio()
>>> function that it will always return a PMD sized folio. Adapt the code so
>>> that it can also work if largest_zero_folio() returns a ZERO_PAGE.
>>>
>>> [...]
>>
>> Applied to the vfs-6.18.iomap branch of the vfs/vfs.git tree.
>> Patches in the vfs-6.18.iomap branch should appear in linux-next soon.
> 
> Hmm, AFAIK largest_zero_folio just showed up in mm.git a few days ago.
> Wouldn't it be better to queue up this change there?
> 
> 

Indeed, compiling vfs/vfs.all as of today fails with:

fs/iomap/direct-io.c:281:36: error: implicit declaration of function 
‘largest_zero_folio’; did you mean ‘is_zero_folio’? 
[-Wimplicit-function-declaration]

Reverting "iomap: use largest_zero_folio() in iomap_dio_zero()" fixes 
the compilation.