linux-kernel - Re: [PATCH v3 1/8] statx: add direct I/O alignment information

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Message-ID: <YrShiIjNCIANjSwL@sol.localdomain>
Date:   Thu, 23 Jun 2022 10:23:20 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     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: [PATCH v3 1/8] statx: add direct I/O alignment information

On Thu, Jun 23, 2022 at 08:58:12AM -0700, Darrick J. Wong wrote:
> > diff --git a/include/linux/stat.h b/include/linux/stat.h
> > index 7df06931f25d8..ff277ced50e9f 100644
> > --- a/include/linux/stat.h
> > +++ b/include/linux/stat.h
> > @@ -50,6 +50,8 @@ struct kstat {
> >  	struct timespec64 btime;			/* File creation time */
> >  	u64		blocks;
> >  	u64		mnt_id;
> > +	u32		dio_mem_align;
> > +	u32		dio_offset_align;
> 
> Hmm.  Does the XFS port of XFS_IOC_DIOINFO to STATX_DIOALIGN look like
> this?
> 
> 	struct xfs_buftarg	*target = xfs_inode_buftarg(ip);
> 
> 	kstat.dio_mem_align = target->bt_logical_sectorsize;
> 	kstat.dio_offset_align = target->bt_logical_sectorsize;
> 	kstat.result_mask |= STATX_DIOALIGN;

Yes, I think so.

However, if we need more fields as Avi Kivity requested at
https://lore.kernel.org/r/6c06b2d4-2d96-c4a6-7aca-5147a91e7cf2@scylladb.com
that is going to complicate things.  I haven't had a chance to look
into whether those extra fields are really needed.  Your opinion on whether XFS
(and any other filesystem) needs them would be appreciated.

> 
> And I guess you're tabling the "optimal" IO discussions for now, because
> there are too many variants of what that means?
> 

Yes, that's omitted for now due to the apparent redundancy with stx_blksize.

- Eric