Re: [PATCH 7/7] iov_iter: remove iov_iter_is_aligned

[Mike Snitzer <snitzer@kernel.org>]

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@kernel.org>
> > > 
> > > No more callers.
> > > 
> > > Signed-off-by: Keith Busch <kbusch@kernel.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.