* [PATCH] block: loop: set discard_granularity as PAGE_SIZE if sb->s_blocksize is 0
@ 2022-01-24 10:06 Ming Lei
2022-01-24 13:36 ` Vivek Goyal
2022-01-24 14:05 ` Christoph Hellwig
0 siblings, 2 replies; 4+ messages in thread
From: Ming Lei @ 2022-01-24 10:06 UTC (permalink / raw)
To: Jens Axboe; +Cc: linux-block, Ming Lei, Vivek Goyal, Pei Zhang
If backing file's filesystem has implemented ->fallocate(), we think the
loop device can support discard, then pass sb->s_blocksize as
discard_granularity. However, some underlying FS, such as overlayfs,
doesn't set sb->s_blocksize, and causes discard_granularity to be set as
zero, then the warning in __blkdev_issue_discard() is triggered.
Fix the issue by setting discard_granularity as PAGE_SIZE in this case
since PAGE_SIZE is the most common data unit for FS.
Cc: Vivek Goyal <vgoyal@redhat.com>
Reported-by: Pei Zhang <pezhang@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
drivers/block/loop.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index b1b05c45c07c..8c15bfab7e1a 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -776,6 +776,10 @@ static void loop_config_discard(struct loop_device *lo)
} else {
max_discard_sectors = UINT_MAX >> 9;
granularity = inode->i_sb->s_blocksize;
+
+ /* Take PAGE_SIZE if the FS doesn't provide us one hint */
+ if (!granularity)
+ granularity = PAGE_SIZE;
}
if (max_discard_sectors) {
--
2.31.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] block: loop: set discard_granularity as PAGE_SIZE if sb->s_blocksize is 0
2022-01-24 10:06 [PATCH] block: loop: set discard_granularity as PAGE_SIZE if sb->s_blocksize is 0 Ming Lei
@ 2022-01-24 13:36 ` Vivek Goyal
2022-01-24 14:05 ` Christoph Hellwig
1 sibling, 0 replies; 4+ messages in thread
From: Vivek Goyal @ 2022-01-24 13:36 UTC (permalink / raw)
To: Ming Lei
Cc: Jens Axboe, linux-block, Pei Zhang, Miklos Szeredi, linux-unionfs
On Mon, Jan 24, 2022 at 06:06:28PM +0800, Ming Lei wrote:
> If backing file's filesystem has implemented ->fallocate(), we think the
> loop device can support discard, then pass sb->s_blocksize as
> discard_granularity. However, some underlying FS, such as overlayfs,
> doesn't set sb->s_blocksize, and causes discard_granularity to be set as
> zero, then the warning in __blkdev_issue_discard() is triggered.
[ Copying linux-unionfs and Miklos ]
Miklos mentioned that it might be ok to copy upper->s_blocksize into
ovl->s_blocksize in overlayfs as other anonymous filesystem set it to
some value (nfs, 9p, fuse, cifs) as well.
So it might be reasonable to fix overlayfs as well. But I think we need
a block layer fix as well to deal with any filesystem which supports
->fallocate() and does not advertize ->s_blocksize. Not advertizing
->s_blocksize will probably only lead to suboptimial performance and
nothing more.
>
> Fix the issue by setting discard_granularity as PAGE_SIZE in this case
> since PAGE_SIZE is the most common data unit for FS.
>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Reported-by: Pei Zhang <pezhang@redhat.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Vivek
> ---
> drivers/block/loop.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index b1b05c45c07c..8c15bfab7e1a 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -776,6 +776,10 @@ static void loop_config_discard(struct loop_device *lo)
> } else {
> max_discard_sectors = UINT_MAX >> 9;
> granularity = inode->i_sb->s_blocksize;
> +
> + /* Take PAGE_SIZE if the FS doesn't provide us one hint */
> + if (!granularity)
> + granularity = PAGE_SIZE;
> }
>
> if (max_discard_sectors) {
> --
> 2.31.1
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] block: loop: set discard_granularity as PAGE_SIZE if sb->s_blocksize is 0
2022-01-24 10:06 [PATCH] block: loop: set discard_granularity as PAGE_SIZE if sb->s_blocksize is 0 Ming Lei
2022-01-24 13:36 ` Vivek Goyal
@ 2022-01-24 14:05 ` Christoph Hellwig
2022-01-24 15:22 ` Vivek Goyal
1 sibling, 1 reply; 4+ messages in thread
From: Christoph Hellwig @ 2022-01-24 14:05 UTC (permalink / raw)
To: Ming Lei; +Cc: Jens Axboe, linux-block, Vivek Goyal, Pei Zhang
On Mon, Jan 24, 2022 at 06:06:28PM +0800, Ming Lei wrote:
> If backing file's filesystem has implemented ->fallocate(), we think the
> loop device can support discard, then pass sb->s_blocksize as
> discard_granularity. However, some underlying FS, such as overlayfs,
> doesn't set sb->s_blocksize, and causes discard_granularity to be set as
> zero, then the warning in __blkdev_issue_discard() is triggered.
>
> Fix the issue by setting discard_granularity as PAGE_SIZE in this case
> since PAGE_SIZE is the most common data unit for FS.
sb->s_blocksize really does not mean anything. kstat.blksize might
be a better choice, even if it someimes errs on the too large side.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] block: loop: set discard_granularity as PAGE_SIZE if sb->s_blocksize is 0
2022-01-24 14:05 ` Christoph Hellwig
@ 2022-01-24 15:22 ` Vivek Goyal
0 siblings, 0 replies; 4+ messages in thread
From: Vivek Goyal @ 2022-01-24 15:22 UTC (permalink / raw)
To: Christoph Hellwig
Cc: Ming Lei, Jens Axboe, linux-block, Pei Zhang, Miklos Szeredi,
linux-unionfs
On Mon, Jan 24, 2022 at 06:05:07AM -0800, Christoph Hellwig wrote:
> On Mon, Jan 24, 2022 at 06:06:28PM +0800, Ming Lei wrote:
> > If backing file's filesystem has implemented ->fallocate(), we think the
> > loop device can support discard, then pass sb->s_blocksize as
> > discard_granularity. However, some underlying FS, such as overlayfs,
> > doesn't set sb->s_blocksize, and causes discard_granularity to be set as
> > zero, then the warning in __blkdev_issue_discard() is triggered.
> >
> > Fix the issue by setting discard_granularity as PAGE_SIZE in this case
> > since PAGE_SIZE is the most common data unit for FS.
>
> sb->s_blocksize really does not mean anything. kstat.blksize might
> be a better choice, even if it someimes errs on the too large side.
[ CC linux-unionfs, Miklos ]
This should work well for overlayfs too. I see it just passes the query
to underlying filesystem and that should report optimal I/O size.
On my overlayfs instance, I see.
# stat -c '%o' foo.txt
4096
Vivek
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-01-24 15:22 UTC | newest]
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2022-01-24 10:06 [PATCH] block: loop: set discard_granularity as PAGE_SIZE if sb->s_blocksize is 0 Ming Lei
2022-01-24 13:36 ` Vivek Goyal
2022-01-24 14:05 ` Christoph Hellwig
2022-01-24 15:22 ` Vivek Goyal
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