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From: Nikolay Borisov <nborisov@suse.com>
To: Josef Bacik <josef@toxicpanda.com>
Cc: linux-btrfs@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH 5/8] btrfs: don't enospc all tickets on flush failure
Date: Wed, 28 Nov 2018 10:11:21 +0200
Message-ID: <684d2544-315c-330a-f0be-925963019c8a@suse.com> (raw)
In-Reply-To: <20181127194601.sdl3qhekvixvevgu@macbook-pro-91.dhcp.thefacebook.com>



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
> 

  reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-21 19:03 [PATCH 0/8] Enospc cleanups and fixes Josef Bacik
2018-11-21 19:03 ` [PATCH 1/8] btrfs: check if free bgs for commit Josef Bacik
2018-11-26 10:45   ` Nikolay Borisov
2018-11-21 19:03 ` [PATCH 2/8] btrfs: dump block_rsv whe dumping space info Josef Bacik
2018-11-21 19:03 ` [PATCH 3/8] btrfs: don't use global rsv for chunk allocation Josef Bacik
2018-11-26 11:25   ` Nikolay Borisov
2018-11-21 19:03 ` [PATCH 4/8] btrfs: add ALLOC_CHUNK_FORCE to the flushing code Josef Bacik
2018-11-26 11:28   ` Nikolay Borisov
2018-11-21 19:03 ` [PATCH 5/8] btrfs: don't enospc all tickets on flush failure Josef Bacik
2018-11-26 12:25   ` Nikolay Borisov
2018-11-27 19:46     ` Josef Bacik
2018-11-28  8:11       ` Nikolay Borisov [this message]
2018-11-21 19:03 ` [PATCH 6/8] btrfs: loop in inode_rsv_refill Josef Bacik
2018-11-21 19:03 ` [PATCH 7/8] btrfs: be more explicit about allowed flush states Josef Bacik
2018-11-26 12:41   ` Nikolay Borisov
2018-11-26 12:45     ` Nikolay Borisov
2018-11-21 19:03 ` [PATCH 8/8] btrfs: reserve extra space during evict() Josef Bacik
2018-12-03 15:24 [PATCH 0/8][V2] Enospc cleanups and fixeS Josef Bacik
2018-12-03 15:24 ` [PATCH 5/8] btrfs: don't enospc all tickets on flush failure Josef Bacik
2018-12-11 14:32   ` Nikolay Borisov

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