Re: [PATCH AUTOSEL 4.18 107/113] btrfs: Rewrite retry logic in do_chunk_alloc

[Sasha Levin <Alexander.Levin@microsoft.com>]

On Wed, Sep 05, 2018 at 11:22:32AM +0200, David Sterba wrote:
>On Thu, Aug 30, 2018 at 06:08:33PM +0000, Sasha Levin wrote:
>> From: Nikolay Borisov <nborisov@suse.com>
>>
>> [ Upstream commit 2556fbb0bead7929ddf67f8b4184f434cee4e7d7 ]
>>
>> do_chunk_alloc implements logic to detect whether there is currently
>> pending chunk allocation (by means of space_info->chunk_alloc being
>> set) and if so it loops around to the 'again' label. Additionally,
>> based on the state of the space_info (e.g. whether it's full or not)
>> and the return value of should_alloc_chunk() it decides whether this
>> is a "hard" error (ENOSPC) or we can just return 0.
>>
>> This patch refactors all of this:
>>
>> 1. Put order to the scattered ifs handling the various cases in an
>> easy-to-read if {} else if{} branches. This makes clear the various
>> cases we are interested in handling.
>>
>> 2. Call should_alloc_chunk only once and use the result in the
>> if/else if constructs. All of this is done under space_info->lock, so
>> even before multiple calls of should_alloc_chunk were unnecessary.
>>
>> 3. Rewrite the "do {} while()" loop currently implemented via label
>> into an explicit loop construct.
>>
>> 4. Move the mutex locking for the case where the caller is the one doing
>> the allocation. For the case where the caller needs to wait a concurrent
>> allocation, introduce a pair of mutex_lock/mutex_unlock to act as a
>> barrier and reword the comment.
>>
>> 5. Switch local vars to bool type where pertinent.
>>
>> All in all this shouldn't introduce any functional changes.
>
>Unless there are other followup patches "No functional changes" is a
>hint for autosel not to pick the patch.

Out it goes, thanks!