On 27.11.18 г. 21:46 ч., Josef Bacik wrote:
> On Mon, Nov 26, 2018 at 02:25:52PM +0200, Nikolay Borisov wrote:
>>
>>
>> On 21.11.18 г. 21:03 ч., Josef Bacik wrote:
>>> With the introduction of the per-inode block_rsv it became possible to
>>> have really really large reservation requests made because of data
>>> fragmentation. Since the ticket stuff assumed that we'd always have
>>> relatively small reservation requests it just killed all tickets if we
>>> were unable to satisfy the current request. However this is generally
>>> not the case anymore. So fix this logic to instead see if we had a
>>> ticket that we were able to give some reservation to, and if we were
>>> continue the flushing loop again. Likewise we make the tickets use the
>>> space_info_add_old_bytes() method of returning what reservation they did
>>> receive in hopes that it could satisfy reservations down the line.
>>
>>
>> The logic of the patch can be summarised as follows:
>>
>> If no progress is made for a ticket, then start fail all tickets until
>> the first one that has progress made on its reservation (inclusive). In
>> this case this first ticket will be failed but at least it's space will
>> be reused via space_info_add_old_bytes.
>>
>> Frankly this seem really arbitrary.
>
> It's not though. The tickets are in order of who requested the reservation.
> Because we will backfill reservations for things like hugely fragmented files
> or
> large amounts of delayed refs we can have spikes where we're trying to reserve
> 100mb's of metadata space. We may fill 50mb of that before we run out of
> space.
> Well so we can't satisfy that reservation, but the small 100k reservations
> that
> are waiting to be serviced can be satisfied and they can run. The alternative
> is you get ENOSPC and then you can turn around and touch a file no problem
> because it's a small reservation and there was room for it. This patch
> enables
> better behavior for the user. Thanks,
Well this information needs to be in the changelog since it describe the
situation where this patch is useful.
>
> Josef
>
