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From: Vivek Goyal <vgoyal@redhat.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, Pei Zhang <pezhang@redhat.com>,
	Miklos Szeredi <miklos@szeredi.hu>,
	linux-unionfs@vger.kernel.org
Subject: Re: [PATCH] block: loop: set discard_granularity as PAGE_SIZE if sb->s_blocksize is 0
Date: Mon, 24 Jan 2022 10:22:01 -0500	[thread overview]
Message-ID: <Ye7EGS2eYzhJX/e0@redhat.com> (raw)
In-Reply-To: <Ye6yE2Ephyv+WBYY@infradead.org>

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


      parent reply	other threads:[~2022-01-24 15:22 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20220124100628.1327718-1-ming.lei@redhat.com>
2022-01-24 13:36 ` [PATCH] block: loop: set discard_granularity as PAGE_SIZE if sb->s_blocksize is 0 Vivek Goyal
     [not found] ` <Ye6yE2Ephyv+WBYY@infradead.org>
2022-01-24 15:22   ` Vivek Goyal [this message]

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