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

[Nikolay Borisov <nborisov@suse.com>]

On 15.07.2017 10:09, Omar Sandoval wrote:
> 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.

It's failing even on current upstream kernels with premature ENOSPC.

>