* Purpose of block reserves
@ 2010-12-09 8:34 Arne Jansen
2010-12-10 8:37 ` Arne Jansen
0 siblings, 1 reply; 2+ messages in thread
From: Arne Jansen @ 2010-12-09 8:34 UTC (permalink / raw)
To: linux-btrfs; +Cc: yanzheng
Hi,
while reading btrfs source code, I try to make sense of the various uses
of block reserves. The working theory is as follows:
1. Every operation has to reserve upfront every single byte it needs to
complete its operation fully.
2. If an operation cannot determine how much space it will need, it has
to be able to cope with running out of space. Normally it does it by
inserting an orphan item, doing its work in multiple transactions and
removing the orphan item. The commits in between normally free up enough
space to continue the operation.
3. All other enospc situations are errors in program logic and should result
in BUG_ON.
It would be great of someone with a deeper knowledge could correct, expand
or just confirm this.
Thanks,
Arne
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Purpose of block reserves
2010-12-09 8:34 Purpose of block reserves Arne Jansen
@ 2010-12-10 8:37 ` Arne Jansen
0 siblings, 0 replies; 2+ messages in thread
From: Arne Jansen @ 2010-12-10 8:37 UTC (permalink / raw)
To: linux-btrfs; +Cc: yanzheng
Arne Jansen wrote:
>
> while reading btrfs source code, I try to make sense of the various uses
> of block reserves. The working theory is as follows:
Since there have been no protests, I added this information to the wiki, section
"Code documentation".
--
Arne
>
> 1. Every operation has to reserve upfront every single byte it needs to
> complete its operation fully.
> 2. If an operation cannot determine how much space it will need, it has
> to be able to cope with running out of space. Normally it does it by
> inserting an orphan item, doing its work in multiple transactions and
> removing the orphan item. The commits in between normally free up enough
> space to continue the operation.
> 3. All other enospc situations are errors in program logic and should result
> in BUG_ON.
>
> It would be great of someone with a deeper knowledge could correct, expand
> or just confirm this.
>
> Thanks,
> Arne
> --
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