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

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Message-ID: <43bca78e-fa89-4b0e-94f1-de7385818950@samsung.com>
Date: Mon, 18 Aug 2025 16:35:04 +0200
From: Pankaj Raghav <p.raghav@...sung.com>
To: André Almeida <andrealmeid@...lia.com>, Christoph
	Hellwig <hch@...radead.org>, Christian Brauner <brauner@...nel.org>,
	<akpm@...ux-foundation.org>, Stephen Rothwell <sfr@...b.auug.org.au>
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>
Subject: Re: [PATCH] iomap: use largest_zero_folio() in iomap_dio_zero()

On 18/08/2025 16:12, André Almeida wrote:
> 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.
> 

I also got some reports from Stephen in linux-next. As Christoph 
suggested, maybe we drop the patches from Christian's tree and queue it 
up via Andrew's tree

--
Pankaj