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

[Chris Mason <clm@fb.com>]

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.

-chris