linux-kernel - Re: [RFC PATCH v2 1/7] statx: add I/O alignment information

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Date:   Wed, 15 Jun 2022 06:12:04 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Dave Chinner <david@...morbit.com>,
        "Darrick J. Wong" <djwong@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, linux-xfs@...r.kernel.org,
        linux-api@...r.kernel.org, linux-fscrypt@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Keith Busch <kbusch@...nel.org>
Subject: Re: [RFC PATCH v2 1/7] statx: add I/O alignment information

On Mon, Jun 13, 2022 at 10:25:12PM -0700, Eric Biggers wrote:
> While working on the man-pages update, I'm having second thoughts about the
> stx_offset_align_optimal field.  Does any filesystem other than XFS actually
> want stx_offset_align_optimal, when st[x]_blksize already exists?  Many network
> filesystems, as well as tmpfs when hugepages are enabled, already report large
> (megabytes) sizes in st[x]_blksize.  And all documentation I looked at (man
> pages for Linux, POSIX, FreeBSD, NetBSD, macOS) documents st_blksize as
> something like "the preferred blocksize for efficient I/O".  It's never
> documented as being limited to PAGE_SIZE, which makes sense because it's not.

Yes.  While st_blksize is utterly misnamed, it has always aways been
the optimal I/O size.

> Perhaps for now we should just add STATX_DIOALIGN instead of STATX_IOALIGN,
> leaving out the stx_offset_align_optimal field?  What do people think?

Yes, this sounds like a good plan.