[PATCH] iomap: use largest_zero_folio() in iomap_dio_zero()

[PATCH] iomap: use largest_zero_folio() in iomap_dio_zero()

[Pankaj Raghav (Samsung)]

From: Pankaj Raghav <p.raghav@samsung.com>

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.

Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
---
 fs/iomap/direct-io.c | 38 +++++++++++++++-----------------------
 1 file changed, 15 insertions(+), 23 deletions(-)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index b84f6af2eb4c..a7a281ea3e50 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -24,13 +24,6 @@
 #define IOMAP_DIO_WRITE		(1U << 30)
 #define IOMAP_DIO_DIRTY		(1U << 31)
 
-/*
- * Used for sub block zeroing in iomap_dio_zero()
- */
-#define IOMAP_ZERO_PAGE_SIZE (SZ_64K)
-#define IOMAP_ZERO_PAGE_ORDER (get_order(IOMAP_ZERO_PAGE_SIZE))
-static struct page *zero_page;
-
 struct iomap_dio {
 	struct kiocb		*iocb;
 	const struct iomap_dio_ops *dops;
@@ -285,24 +278,35 @@ static int iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
 {
 	struct inode *inode = file_inode(dio->iocb->ki_filp);
 	struct bio *bio;
+	struct folio *zero_folio = largest_zero_folio();
+	int nr_vecs = max(1, i_blocksize(inode) / folio_size(zero_folio));
 
 	if (!len)
 		return 0;
+
 	/*
-	 * Max block size supported is 64k
+	 * This limit shall never be reached as most filesystems have a
+	 * maximum blocksize of 64k.
 	 */
-	if (WARN_ON_ONCE(len > IOMAP_ZERO_PAGE_SIZE))
+	if (WARN_ON_ONCE(nr_vecs > BIO_MAX_VECS))
 		return -EINVAL;
 
-	bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
+	bio = iomap_dio_alloc_bio(iter, dio, nr_vecs,
+				  REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
 	fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
 				  GFP_KERNEL);
 	bio->bi_iter.bi_sector = iomap_sector(&iter->iomap, pos);
 	bio->bi_private = dio;
 	bio->bi_end_io = iomap_dio_bio_end_io;
 
-	__bio_add_page(bio, zero_page, len, 0);
+	while (len > 0) {
+		unsigned int io_len = min(len, folio_size(zero_folio));
+
+		bio_add_folio_nofail(bio, zero_folio, io_len, 0);
+		len -= io_len;
+	}
 	iomap_dio_submit_bio(iter, dio, bio, pos);
+
 	return 0;
 }
 
@@ -822,15 +826,3 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 	return iomap_dio_complete(dio);
 }
 EXPORT_SYMBOL_GPL(iomap_dio_rw);
-
-static int __init iomap_dio_init(void)
-{
-	zero_page = alloc_pages(GFP_KERNEL | __GFP_ZERO,
-				IOMAP_ZERO_PAGE_ORDER);
-
-	if (!zero_page)
-		return -ENOMEM;
-
-	return 0;
-}
-fs_initcall(iomap_dio_init);

base-commit: 931e46dcbc7e6035a90e9c4a27a84b660e083f0a
-- 
2.50.1

Re: [PATCH] iomap: use largest_zero_folio() in iomap_dio_zero()

[Darrick J. Wong]

On Thu, Aug 14, 2025 at 04:21:37PM +0200, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@samsung.com>
> 
> 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.
> 
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>

Seems fine to me, though I wonder if this oughn't go along with the
rest of the largest_zero_folio changes?

Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  fs/iomap/direct-io.c | 38 +++++++++++++++-----------------------
>  1 file changed, 15 insertions(+), 23 deletions(-)
> 
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index b84f6af2eb4c..a7a281ea3e50 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -24,13 +24,6 @@
>  #define IOMAP_DIO_WRITE		(1U << 30)
>  #define IOMAP_DIO_DIRTY		(1U << 31)
>  
> -/*
> - * Used for sub block zeroing in iomap_dio_zero()
> - */
> -#define IOMAP_ZERO_PAGE_SIZE (SZ_64K)
> -#define IOMAP_ZERO_PAGE_ORDER (get_order(IOMAP_ZERO_PAGE_SIZE))
> -static struct page *zero_page;
> -
>  struct iomap_dio {
>  	struct kiocb		*iocb;
>  	const struct iomap_dio_ops *dops;
> @@ -285,24 +278,35 @@ static int iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
>  {
>  	struct inode *inode = file_inode(dio->iocb->ki_filp);
>  	struct bio *bio;
> +	struct folio *zero_folio = largest_zero_folio();
> +	int nr_vecs = max(1, i_blocksize(inode) / folio_size(zero_folio));
>  
>  	if (!len)
>  		return 0;
> +
>  	/*
> -	 * Max block size supported is 64k
> +	 * This limit shall never be reached as most filesystems have a
> +	 * maximum blocksize of 64k.
>  	 */
> -	if (WARN_ON_ONCE(len > IOMAP_ZERO_PAGE_SIZE))
> +	if (WARN_ON_ONCE(nr_vecs > BIO_MAX_VECS))
>  		return -EINVAL;
>  
> -	bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
> +	bio = iomap_dio_alloc_bio(iter, dio, nr_vecs,
> +				  REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
>  	fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
>  				  GFP_KERNEL);
>  	bio->bi_iter.bi_sector = iomap_sector(&iter->iomap, pos);
>  	bio->bi_private = dio;
>  	bio->bi_end_io = iomap_dio_bio_end_io;
>  
> -	__bio_add_page(bio, zero_page, len, 0);
> +	while (len > 0) {
> +		unsigned int io_len = min(len, folio_size(zero_folio));
> +
> +		bio_add_folio_nofail(bio, zero_folio, io_len, 0);
> +		len -= io_len;
> +	}
>  	iomap_dio_submit_bio(iter, dio, bio, pos);
> +
>  	return 0;
>  }
>  
> @@ -822,15 +826,3 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>  	return iomap_dio_complete(dio);
>  }
>  EXPORT_SYMBOL_GPL(iomap_dio_rw);
> -
> -static int __init iomap_dio_init(void)
> -{
> -	zero_page = alloc_pages(GFP_KERNEL | __GFP_ZERO,
> -				IOMAP_ZERO_PAGE_ORDER);
> -
> -	if (!zero_page)
> -		return -ENOMEM;
> -
> -	return 0;
> -}
> -fs_initcall(iomap_dio_init);
> 
> base-commit: 931e46dcbc7e6035a90e9c4a27a84b660e083f0a
> -- 
> 2.50.1
> 
> 

Re: [PATCH] iomap: use largest_zero_folio() in iomap_dio_zero()

[Pankaj Raghav (Samsung)]

On Thu, Aug 14, 2025 at 11:27:13AM -0700, Darrick J. Wong wrote:
> On Thu, Aug 14, 2025 at 04:21:37PM +0200, Pankaj Raghav (Samsung) wrote:
> > From: Pankaj Raghav <p.raghav@samsung.com>
> > 
> > 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.
> > 
> > Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> 
> Seems fine to me, though I wonder if this oughn't go along with the
> rest of the largest_zero_folio changes?

I included them in one of the early versions but later removed as we had
to rework the implementation multiple times. I just wanted to reduce the
scope of the series and send out changes that uses the API separately :).

> 
> Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

Thanks!

-- 
Pankaj Raghav

Re: [PATCH] iomap: use largest_zero_folio() in iomap_dio_zero()

[Christian Brauner]

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.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs-6.18.iomap

[1/1] iomap: use largest_zero_folio() in iomap_dio_zero()
      https://git.kernel.org/vfs/vfs/c/5589673e8d8d

Re: [PATCH] iomap: use largest_zero_folio() in iomap_dio_zero()

[Christoph Hellwig]

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?

Re: [PATCH] iomap: use largest_zero_folio() in iomap_dio_zero()

[André Almeida]

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.

Re: [PATCH] iomap: use largest_zero_folio() in iomap_dio_zero()

[Pankaj Raghav]

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

Re: [PATCH] iomap: use largest_zero_folio() in iomap_dio_zero()

[Andrew Morton]

On Mon, 18 Aug 2025 16:35:04 +0200 Pankaj Raghav <p.raghav@samsung.com> wrote:

> >>> 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

Thanks, I added it to mm.git.

Re: [PATCH] iomap: use largest_zero_folio() in iomap_dio_zero()

[Christian Brauner]

On Mon, Aug 18, 2025 at 08:14:03PM -0700, Andrew Morton wrote:
> On Mon, 18 Aug 2025 16:35:04 +0200 Pankaj Raghav <p.raghav@samsung.com> wrote:
> 
> > >>> 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
> 
> Thanks, I added it to mm.git.

Please ask before you move stuff around between trees. You've complained
to me before about this before too. I haven't agreed to that at all.

There's a bunch more iomap work coming and this will most certainly not
start going through mm trees. So if there's merge conflicts where we
rely on a helper that's in mm-next the good thing would simply to
provide a branch for us with that helper that we can base this off of.