linux-kernel - Re: [PATCH 7/7] iov_iter: remove iov_iter_is

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Message-ID: <aJDReEEeiVBWEYLy@kernel.org>
Date: Mon, 4 Aug 2025 11:27:52 -0400
From: Mike Snitzer <snitzer@...nel.org>
To: Keith Busch <kbusch@...nel.org>
Cc: Keith Busch <kbusch@...a.com>, linux-block@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	axboe@...nel.dk, dw@...idwei.uk, brauner@...nel.org,
	Chuck Lever <chuck.lever@...cle.com>, linux-nfs@...r.kernel.org
Subject: Re: [PATCH 7/7] iov_iter: remove iov_iter_is_aligned

On Mon, Aug 04, 2025 at 11:25:08AM -0400, Mike Snitzer wrote:
> On Mon, Aug 04, 2025 at 08:16:39AM -0600, Keith Busch wrote:
> > On Fri, Aug 01, 2025 at 10:02:49PM -0400, Mike Snitzer wrote:
> > > On Fri, Aug 01, 2025 at 04:47:36PM -0700, Keith Busch wrote:
> > > > From: Keith Busch <kbusch@...nel.org>
> > > > 
> > > > No more callers.
> > > > 
> > > > Signed-off-by: Keith Busch <kbusch@...nel.org>
> > > 
> > > You had me up until this last patch.
> > > 
> > > I'm actually making use of iov_iter_is_aligned() in a series of
> > > changes for both NFS and NFSD.  Chuck has included some of the
> > > NFSD changes in his nfsd-testing branch, see:
> > > https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git/commit/?h=nfsd-testing&id=5d78ac1e674b45f9c9e3769b48efb27c44f4e4d3
> > > 
> > > And the balance of my work that is pending review/inclusion is:
> > > https://lore.kernel.org/linux-nfs/20250731230633.89983-1-snitzer@kernel.org/
> > > https://lore.kernel.org/linux-nfs/20250801171049.94235-1-snitzer@kernel.org/
> > > 
> > > I only need iov_iter_aligned_bvec, but recall I want to relax its
> > > checking with this patch:
> > > https://lore.kernel.org/linux-nfs/20250708160619.64800-5-snitzer@kernel.org/
> > > 
> > > Should I just add iov_iter_aligned_bvec() to fs/nfs_common/ so that
> > > both NFS and NFSD can use it?
> > 
> > If at all possible, I recommend finding a place that already walks the
> > vectors and do an opprotunistic check for the alignments there. This
> > will save CPU cycles. For example, nfsd_iter_read already iterates the
> > bvec while setting each page. Could you check the alignment while doing
> > that instead of iterating a second time immediately after?
> 
> Nice goal, I'll see if I can pull it off.
> 
> I'm currently using iov_iter_is_aligned() in 3 new call sites (for
> READ and WRITE) in both NFS and NFSD: nfs_local_iter_init,
> nfsd_iter_read, nfsd_vfs_write
> 
> nfsd_vfs_write is the only one that doesn't iterate the bvec as-is,
> but it does work that _should_ obviate the need to doable check the
> alignment.

Freudian typo: s/doable/double/ :)