Re: [PATCH v2] iomap: skip pages past eof in iomap_do_writepage()

[Dave Chinner <david@fromorbit.com>]

On Sat, Jun 11, 2022 at 07:34:01PM -0400, Chris Mason wrote:
> On 6/9/22 5:15 PM, Chris Mason wrote:
> > On 6/8/22 8:53 PM, Dave Chinner wrote:
> 
> > > Reviewed-by: Dave Chinner <dchinner@redhat.com>
> > 
> > Thanks!  Johannes and I are both going on vacation, but I'll get an
> > experiment rolled to enough hosts to see if the long tails get shorter.
> >  We're unlikely to come back with results before July.
> > 
> 
> Of course, the easiest way to test my theory is live patching against v5.6,
> but there's a wrinkle because v5.6 still has xfs_vm_writepage()
> 
> Looks like the iomap conversion deleted the warning that Jan was originally
> fixing, and I went through some hoops to trigger skipping the pages from
> inside writepage().  As you noted in the commit to delete writepage, this is
> pretty hard to trigger but it does happen once I get down to a few hundred
> MB free.  It doesn't seem to impact fsx runs or other load, and we
> unmount/xfs_repair cleanly.
>
> I don't like to ask people to think about ancient kernels, but am I missing
> any huge problems?  I've got this patch backported on v5.6, and writepage is
> still in place.

Just backport the patch to remove ->writepage as well? I've run test
kernels since ~2017 with the writepage delete in it and never seen
any problems as a result of it. That would seem to me to be the
simplest way of avoiding unexpected issues with reclaim writeback
and truncate races...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com