Re: [PATCH] Btrfs: fix early ENOSPC due to delalloc

[Omar Sandoval <osandov@osandov.com>]

On Sat, Jul 15, 2017 at 09:43:18AM +0300, Nikolay Borisov wrote:
> 
> 
> On 15.07.2017 00:36, Omar Sandoval wrote:
> > On Thu, Jul 06, 2017 at 10:59:27PM -0700, Omar Sandoval wrote:
> >> From: Omar Sandoval <osandov@fb.com>
> >>
> >> If a lot of metadata is reserved for outstanding delayed allocations, we
> >> rely on shrink_delalloc() to reclaim metadata space in order to fulfill
> >> reservation tickets. However, shrink_delalloc() has a shortcut where if
> >> it determines that space can be overcommitted, it will stop early. This
> >> made sense before the ticketed enospc system, but now it means that
> >> shrink_delalloc() will often not reclaim enough space to fulfill any
> >> tickets, leading to an early ENOSPC. (Reservation tickets don't care
> >> about being able to overcommit, they need every byte accounted for.)
> >>
> >> Fix it by getting rid of the shortcut so that shrink_delalloc() reclaims
> >> all of the metadata it is supposed to. This fixes early ENOSPCs we were
> >> seeing when doing a btrfs receive to populate a new filesystem.
> > 
> > Jeff, Nikolay, did either of you get a chance to test this yet?
> 
> I tested this patch with generic/273 and it didn't prevent ENOSPC there.

Weird, I've never seen generic/273 fail. Anyways, I'm more interested in
the installer ENOSPCs Jeff mentioned.