Re: regression in DIO write behavior

[Jeff Layton <jlayton@redhat.com>]

On Tue, 2017-01-24 at 12:23 -0500, Weston Andros Adamson wrote:
> Hey Jeff,
> 
> That sounds like a regression to me. I don't think it's been around since the
> pgio rework, but maybe?
> 
> -dros
> 

I certainly could be wrong. :)

I did open this bug, and we'll track it down there:

https://bugzilla.redhat.com/show_bug.cgi?id=1416127

Looks like Scott bisected it down in RHEL7 kernels so we should be able
to ID it from there.

Cheers,
Jeff

> > On Jan 24, 2017, at 10:44 AM, Jeff Layton <jlayton@redhat.com> wrote:
> > 
> > I've noticed a probable regression in recent kernels. When you run the
> > attached program on an older kernel (I used 2.6.32-642.6.2.el6.x86_64),
> > I see the kernel generate wsize WRITE calls on the wire.
> > 
> > When I run the same program on a more modern kernel (mainline as of
> > today), it generates a ton of page-sized I/Os instead. I've verified
> > that iov_iter_get_pages_alloc is returning a wsize array of pages, it
> > just seems like the request handling code isn't stitching them together
> > like it should.
> > 
> > Is this an expected change or a regression? I'm guessing the latter, and
> > that it might have crept in during the pageio rework from a couple of
> > years ago.
> > 
> > Any idea where the bug might be?
> > -- 
> > Jeff Layton <jlayton@redhat.com><diotest2.c>
> 
> 

-- 
Jeff Layton <jlayton@redhat.com>