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Subject: Re: [PATCH v3 00/12] block: always associate blkg and refcount
 cleanup
To:     Dennis Zhou <dennisszhou@gmail.com>
Cc:     Tejun Heo <tj@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>,
        Josef Bacik <josef@toxicpanda.com>, kernel-team@fb.com,
        linux-block@vger.kernel.org, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20180911184137.35897-1-dennisszhou@gmail.com>
 <20180921205640.GA50648@dennisz-mbp.dhcp.thefacebook.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <b1bcc8b3-f15f-08e3-e5e0-c1877fba144e@kernel.dk>
Date:   Fri, 21 Sep 2018 20:29:51 -0600
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On 9/21/18 2:56 PM, Dennis Zhou wrote:
> Hi Jens,
> 
> On Tue, Sep 11, 2018 at 02:41:25PM -0400, Dennis Zhou wrote:
>> Hi everyone,
>>
>> v3: a few minor fixes.
>>   0003: Updated the comment to bio_associate_blkg to reflect closest
>>         association.
>>         Removed a return branch in __bio_lookup_create.
>>   0009: Removed an unnecessary rcu_read_(un)lock pair.
>>   0010: Fixed blkg null pointer... blkg->blkcg => blkcg.
>>
>> This is rebased onto axboe#for-4.20/block 902d53914f64.
>>
>> From v2 below (updated):
>> ------
>> This is a followup to the patch series I sent out earlier [1] containing
>> the middle two points:
>>   1. always associate a bio with a blkg
>>   2. remove the extra css ref held by bios and utilize the blkg ref
>>
>> The major difference with v2 is that error handling on blkg creation
>> and association failure is handled more gracefully. Rather than having
>> the complex logic to fallback to root, failures walk up the blkg tree.
>> This seems more natural and less prone to error with the many possible
>> failure scenarios.
>>
>> Additionally, there are fixes for kbuild errors and some key details
>> overlooked by me in the first series that were pointed out in review.
>>
>> Modified from the first patchset:
>> First, both blk-throttle and blk-iolatency rely on blkg association
>> to enable their policies. Rather than each policy (and future policies)
>> implement this logic independently, this consolidates it such that
>> all bios are tagged with a blkg.
>>
>> Second, with the addition of always having a blkg reference, the blkcg
>> can now be referenced through it rather than maintaining an additional
>> pointer and reference. So let's clean this up.
>>
>> [1] https://lore.kernel.org/lkml/20180831015356.69796-1-dennisszhou@gmail.com/T
>>
>> This patchset contains the following 12 patches:
>>   0001-blkcg-fix-ref-count-issue-with-bio_blkcg-using-task_.patch
>>   0002-blkcg-update-blkg_lookup_create-to-do-locking.patch
>>   0003-blkcg-convert-blkg_lookup_create-to-find-closest-blk.patch
>>   0004-blkcg-always-associate-a-bio-with-a-blkg.patch
>>   0005-blkcg-consolidate-bio_issue_init-to-be-a-part-of-cor.patch
>>   0006-blkcg-associate-a-blkg-for-pages-being-evicted-by-sw.patch
>>   0007-blkcg-associate-writeback-bios-with-a-blkg.patch
>>   0008-blkcg-remove-bio-bi_css-and-instead-use-bio-bi_blkg.patch
>>   0009-blkcg-remove-additional-reference-to-the-css.patch
>>   0010-blkcg-cleanup-and-make-blk_get_rl-use-blkg_lookup_cr.patch
>>   0011-blkcg-change-blkg-reference-counting-to-use-percpu_r.patch
>>   0012-blkcg-rename-blkg_try_get-to-blkg_tryget.patch
>>
>> This patchset is on top of axboe#for-4.20/block 902d53914f64.
>>
>> diffstats below:
>>
>> Dennis Zhou (Facebook) (12):
>>   blkcg: fix ref count issue with bio_blkcg using task_css
>>   blkcg: update blkg_lookup_create to do locking
>>   blkcg: convert blkg_lookup_create to find closest blkg
>>   blkcg: always associate a bio with a blkg
>>   blkcg: consolidate bio_issue_init to be a part of core
>>   blkcg: associate a blkg for pages being evicted by swap
>>   blkcg: associate writeback bios with a blkg
>>   blkcg: remove bio->bi_css and instead use bio->bi_blkg
>>   blkcg: remove additional reference to the css
>>   blkcg: cleanup and make blk_get_rl use blkg_lookup_create
>>   blkcg: change blkg reference counting to use percpu_ref
>>   blkcg: rename blkg_try_get to blkg_tryget
>>
>>  Documentation/admin-guide/cgroup-v2.rst |   8 +-
>>  block/bfq-cgroup.c                      |   4 +-
>>  block/bfq-iosched.c                     |   2 +-
>>  block/bio.c                             | 158 ++++++++++++++++--------
>>  block/blk-cgroup.c                      | 123 ++++++++++++------
>>  block/blk-iolatency.c                   |  26 +---
>>  block/blk-throttle.c                    |  13 +-
>>  block/bounce.c                          |   4 +-
>>  block/cfq-iosched.c                     |   4 +-
>>  drivers/block/loop.c                    |   5 +-
>>  drivers/md/raid0.c                      |   2 +-
>>  fs/buffer.c                             |  10 +-
>>  fs/ext4/page-io.c                       |   2 +-
>>  include/linux/bio.h                     |  23 ++--
>>  include/linux/blk-cgroup.h              | 145 +++++++++++++++-------
>>  include/linux/blk_types.h               |   1 -
>>  include/linux/cgroup.h                  |   2 +
>>  include/linux/writeback.h               |   5 +-
>>  kernel/cgroup/cgroup.c                  |  48 +++++--
>>  kernel/trace/blktrace.c                 |   4 +-
>>  mm/page_io.c                            |   2 +-
>>  21 files changed, 381 insertions(+), 210 deletions(-)
>>
>> Thanks,
>> Dennis
> 
> I reran some basic test again for sanity and it seems to be fine on my
> end. There are at least acks, and some reviewed-by's on the series. Is
> there anything else you think needs to be done before we let this bake
> in for-4.20/for-next?

Looks like it's good to go, I have applied it for 4.20. Thanks Dennis.

-- 
Jens Axboe