From: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>
To: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org,
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khlebnikov-XoJtRXgx1JseBXzfvpsJ4g@public.gmane.org
Subject: Re: [PATCH 06/51] memcg: add mem_cgroup_root_css
Date: Thu, 18 Jun 2015 13:12:27 +0200 [thread overview]
Message-ID: <20150618111227.GA5858@dhcp22.suse.cz> (raw)
In-Reply-To: <20150617182500.GI22637-qYNAdHglDFBN0TnZuCh8vA@public.gmane.org>
On Wed 17-06-15 14:25:00, Tejun Heo wrote:
> Hey, Michal.
>
> On Wed, Jun 17, 2015 at 04:56:42PM +0200, Michal Hocko wrote:
> > On Fri 22-05-15 17:13:20, Tejun Heo wrote:
> > > Add global mem_cgroup_root_css which points to the root memcg css.
> >
> > Is there any reason to using css rather than mem_cgroup other than the
> > structure is not visible outside of memcontrol.c? Because I have a
> > patchset which exports it. It is not merged yet so a move to mem_cgroup
> > could be done later. I am just interested whether there is a stronger
> > reason.
>
> It doesn't really matter either way but I think it makes a bit more
> sense to use css as the common type when external code interacts with
> cgroup controllers. e.g. cgroup writeback interacts with both memcg
> and blkcg and in most cases it doesn't know or care about their
> internal states. Most of what it wants is tracking them and doing
> some common css operations (refcnting, printing and so on) on them.
I see and yes, it makes some sense. I just think we can get rid of the
accessor functions when the struct mem_cgroup is visible and the code
can simply do &{page->}mem_cgroup->css.
> > > This will be used by cgroup writeback support. If memcg is disabled,
> > > it's defined as ERR_PTR(-EINVAL).
> >
> > Hmm. Why EINVAL? I can see only mm/backing-dev.c (in
> > review-cgroup-writeback-switch-20150528 branch) which uses it and that
> > shouldn't even try to compile if !CONFIG_MEMCG no? Otherwise we would
> > simply blow up.
>
> Hmm... the code maybe has changed inbetween but there was something
> which depended on the root css being defined when
> !CONFIG_CGROUP_WRITEBACK or maybe it was on blkcg_root_css and memcg
> side was added for consistency.
I have tried to compile with !CONFIG_MEMCG and !CONFIG_CGROUP_WRITEBACK
without mem_cgroup_root_css defined for this configuration and
mm/backing-dev.c compiles just fine. So maybe we should get rid of it
rather than have a potentially tricky code?
> An ERR_PTR value is non-zero, which
> is an invariant which is often depended upon, while guaranteeing oops
> when deref'd.
Yeah, but css_{get,put} and others consumers of the pointer are not
checking for ERR_PTR. So I think this is really misleading.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2015-06-18 11:12 UTC|newest]
Thread overview: 131+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-22 21:13 [PATCHSET 1/3 v4 block/for-4.2/core] writeback: cgroup writeback support Tejun Heo
2015-05-22 21:13 ` [PATCH 01/51] page_writeback: revive cancel_dirty_page() in a restricted form Tejun Heo
2015-05-22 21:13 ` [PATCH 02/51] memcg: add per cgroup dirty page accounting Tejun Heo
2015-05-22 21:13 ` [PATCH 03/51] blkcg: move block/blk-cgroup.h to include/linux/blk-cgroup.h Tejun Heo
2015-05-22 21:13 ` [PATCH 04/51] update !CONFIG_BLK_CGROUP dummies in include/linux/blk-cgroup.h Tejun Heo
2015-05-22 21:13 ` [PATCH 05/51] blkcg: always create the blkcg_gq for the root blkcg Tejun Heo
2015-05-22 21:13 ` [PATCH 06/51] memcg: add mem_cgroup_root_css Tejun Heo
2015-06-17 14:56 ` Michal Hocko
[not found] ` <20150617145642.GI25056-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org>
2015-06-17 18:25 ` Tejun Heo
[not found] ` <20150617182500.GI22637-qYNAdHglDFBN0TnZuCh8vA@public.gmane.org>
2015-06-18 11:12 ` Michal Hocko [this message]
2015-06-18 17:49 ` Tejun Heo
[not found] ` <20150618174930.GA12934-qYNAdHglDFBN0TnZuCh8vA@public.gmane.org>
2015-06-19 9:18 ` Michal Hocko
[not found] ` <20150619091848.GE4913-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org>
2015-06-19 15:17 ` Tejun Heo
2015-05-22 21:13 ` [PATCH 07/51] blkcg: add blkcg_root_css Tejun Heo
2015-05-22 21:13 ` [PATCH 08/51] cgroup, block: implement task_get_css() and use it in bio_associate_current() Tejun Heo
2015-05-22 21:13 ` [PATCH 09/51] blkcg: implement task_get_blkcg_css() Tejun Heo
2015-05-22 21:13 ` [PATCH 10/51] blkcg: implement bio_associate_blkcg() Tejun Heo
2015-05-22 21:13 ` [PATCH 11/51] memcg: implement mem_cgroup_css_from_page() Tejun Heo
[not found] ` <1432329245-5844-12-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2015-05-22 23:28 ` Johannes Weiner
2015-05-24 21:24 ` Tejun Heo
[not found] ` <20150524212440.GD7099-piEFEHQLUPpN0TnZuCh8vA@public.gmane.org>
2015-05-27 12:58 ` Johannes Weiner
2015-05-27 16:13 ` [PATCH v2 " Tejun Heo
2015-05-27 17:09 ` Johannes Weiner
[not found] ` <20150527170955.GA25324-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
2015-05-27 17:48 ` Tejun Heo
2015-05-27 17:57 ` [PATCH v3 " Tejun Heo
2015-05-28 0:00 ` [PATCH v4 " Tejun Heo
2015-05-22 21:13 ` [PATCH 12/51] writeback: move backing_dev_info->state into bdi_writeback Tejun Heo
2015-05-22 21:13 ` [PATCH 13/51] writeback: move backing_dev_info->bdi_stat[] " Tejun Heo
2015-05-22 21:13 ` [PATCH 14/51] writeback: move bandwidth related fields from backing_dev_info " Tejun Heo
2015-05-22 21:13 ` [PATCH 15/51] writeback: s/bdi/wb/ in mm/page-writeback.c Tejun Heo
2015-05-22 21:13 ` [PATCH 16/51] writeback: move backing_dev_info->wb_lock and ->worklist into bdi_writeback Tejun Heo
2015-06-07 0:49 ` Sasha Levin
2015-06-08 5:57 ` [PATCH block/for-4.2-writeback] v9fs: fix error handling in v9fs_session_init() Tejun Heo
2015-06-08 15:10 ` Jens Axboe
2015-05-22 21:13 ` [PATCH 17/51] writeback: reorganize mm/backing-dev.c Tejun Heo
2015-05-22 21:13 ` [PATCH 18/51] writeback: separate out include/linux/backing-dev-defs.h Tejun Heo
2015-05-22 21:13 ` [PATCH 19/51] bdi: make inode_to_bdi() inline Tejun Heo
2015-06-30 6:47 ` Jan Kara
2015-05-22 21:13 ` [PATCH 20/51] writeback: add @gfp to wb_init() Tejun Heo
2015-05-22 21:13 ` [PATCH 21/51] bdi: separate out congested state into a separate struct Tejun Heo
2015-06-30 9:21 ` Jan Kara
2015-05-22 21:13 ` [PATCH 22/51] writeback: add {CONFIG|BDI_CAP|FS}_CGROUP_WRITEBACK Tejun Heo
2015-06-30 9:37 ` Jan Kara
2015-07-02 1:10 ` Tejun Heo
2015-07-03 10:49 ` Jan Kara
2015-07-03 17:14 ` Tejun Heo
2015-05-22 21:13 ` [PATCH 23/51] writeback: make backing_dev_info host cgroup-specific bdi_writebacks Tejun Heo
2015-06-30 10:14 ` Jan Kara
2015-05-22 21:13 ` [PATCH 24/51] writeback, blkcg: associate each blkcg_gq with the corresponding bdi_writeback_congested Tejun Heo
[not found] ` <1432329245-5844-25-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2015-06-30 9:08 ` Jan Kara
2015-05-22 21:13 ` [PATCH 25/51] writeback: attribute stats to the matching per-cgroup bdi_writeback Tejun Heo
[not found] ` <1432329245-5844-26-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2015-06-30 14:17 ` Jan Kara
2015-05-22 21:13 ` [PATCH 26/51] writeback: let balance_dirty_pages() work on the matching cgroup bdi_writeback Tejun Heo
2015-06-30 14:31 ` Jan Kara
2015-07-02 1:26 ` Tejun Heo
2015-05-22 21:13 ` [PATCH 27/51] writeback: make congestion functions per bdi_writeback Tejun Heo
2015-06-30 14:50 ` Jan Kara
2015-05-22 21:13 ` [PATCH 28/51] writeback, blkcg: restructure blk_{set|clear}_queue_congested() Tejun Heo
[not found] ` <1432329245-5844-29-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2015-06-30 15:02 ` Jan Kara
2015-07-02 1:38 ` Tejun Heo
[not found] ` <20150702013815.GE26440-qYNAdHglDFBN0TnZuCh8vA@public.gmane.org>
2015-07-03 12:16 ` Jan Kara
2015-05-22 21:13 ` [PATCH 29/51] writeback, blkcg: propagate non-root blkcg congestion state Tejun Heo
2015-06-30 15:03 ` Jan Kara
2015-05-22 21:13 ` [PATCH 30/51] writeback: implement and use inode_congested() Tejun Heo
2015-06-30 15:21 ` Jan Kara
2015-07-02 1:46 ` Tejun Heo
2015-07-03 12:17 ` Jan Kara
[not found] ` <20150703121721.GJ23329-+0h/O2h83AeN3ZZ/Hiejyg@public.gmane.org>
2015-07-03 17:07 ` Tejun Heo
2015-07-04 15:12 ` [PATCH block/for-4.3] writeback: explain why @inode is allowed to be NULL for inode_congested() Tejun Heo
2015-07-08 8:12 ` Jan Kara
2015-05-22 21:13 ` [PATCH 31/51] writeback: implement WB_has_dirty_io wb_state flag Tejun Heo
2015-06-30 15:42 ` Jan Kara
2015-05-22 21:13 ` [PATCH 32/51] writeback: implement backing_dev_info->tot_write_bandwidth Tejun Heo
[not found] ` <1432329245-5844-33-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2015-06-30 16:14 ` Jan Kara
2015-06-30 16:42 ` Jan Kara
2015-05-22 21:13 ` [PATCH 33/51] writeback: make bdi_has_dirty_io() take multiple bdi_writeback's into account Tejun Heo
2015-06-30 16:48 ` Jan Kara
[not found] ` <20150630164824.GU7252-+0h/O2h83AeN3ZZ/Hiejyg@public.gmane.org>
2015-07-02 2:01 ` Tejun Heo
2015-05-22 21:13 ` [PATCH 34/51] writeback: don't issue wb_writeback_work if clean Tejun Heo
[not found] ` <1432329245-5844-35-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2015-06-30 16:18 ` Jan Kara
2015-05-22 21:13 ` [PATCH 35/51] writeback: make bdi->min/max_ratio handling cgroup writeback aware Tejun Heo
[not found] ` <1432329245-5844-36-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2015-07-01 7:00 ` Jan Kara
2015-05-22 21:13 ` [PATCH 36/51] writeback: implement bdi_for_each_wb() Tejun Heo
[not found] ` <1432329245-5844-37-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2015-07-01 7:27 ` Jan Kara
2015-07-02 2:22 ` Tejun Heo
[not found] ` <20150702022226.GH26440-qYNAdHglDFBN0TnZuCh8vA@public.gmane.org>
2015-07-03 12:26 ` Jan Kara
2015-07-03 17:06 ` Tejun Heo
2015-05-22 21:13 ` [PATCH 37/51] writeback: remove bdi_start_writeback() Tejun Heo
[not found] ` <1432329245-5844-38-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2015-07-01 7:30 ` Jan Kara
2015-05-22 21:13 ` [PATCH 38/51] writeback: make laptop_mode_timer_fn() handle multiple bdi_writeback's Tejun Heo
[not found] ` <1432329245-5844-39-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2015-07-01 7:32 ` Jan Kara
2015-05-22 21:13 ` [PATCH 39/51] writeback: make writeback_in_progress() take bdi_writeback instead of backing_dev_info Tejun Heo
[not found] ` <1432329245-5844-40-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2015-07-01 7:47 ` Jan Kara
2015-07-02 2:28 ` Tejun Heo
2015-05-22 21:13 ` [PATCH 40/51] writeback: make bdi_start_background_writeback() " Tejun Heo
2015-07-01 7:50 ` Jan Kara
2015-07-02 2:29 ` Tejun Heo
[not found] ` <20150701075009.GA7252-+0h/O2h83AeN3ZZ/Hiejyg@public.gmane.org>
2015-07-06 19:36 ` [PATCH block/for-4.3] writeback: update writeback tracepoints to report cgroup Tejun Heo
2015-07-08 8:17 ` Jan Kara
2015-05-22 21:13 ` [PATCH 41/51] writeback: make wakeup_flusher_threads() handle multiple bdi_writeback's Tejun Heo
2015-07-01 8:15 ` Jan Kara
2015-07-02 2:37 ` Tejun Heo
2015-07-03 13:02 ` Jan Kara
[not found] ` <20150703130213.GM23329-+0h/O2h83AeN3ZZ/Hiejyg@public.gmane.org>
2015-07-03 16:33 ` Tejun Heo
2015-05-22 21:13 ` [PATCH 42/51] writeback: make wakeup_dirtytime_writeback() " Tejun Heo
2015-07-01 8:20 ` Jan Kara
2015-05-22 21:13 ` [PATCH 43/51] writeback: add wb_writeback_work->auto_free Tejun Heo
2015-05-22 21:13 ` [PATCH 44/51] writeback: implement bdi_wait_for_completion() Tejun Heo
[not found] ` <1432329245-5844-45-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2015-07-01 16:04 ` Jan Kara
2015-07-02 3:06 ` Tejun Heo
2015-07-03 12:36 ` Jan Kara
2015-07-03 17:02 ` Tejun Heo
2015-07-01 16:09 ` Jan Kara
[not found] ` <20150701160918.GH7252-+0h/O2h83AeN3ZZ/Hiejyg@public.gmane.org>
2015-07-02 3:01 ` Tejun Heo
2015-05-22 21:13 ` [PATCH 45/51] writeback: implement wb_wait_for_single_work() Tejun Heo
2015-07-01 19:07 ` Jan Kara
2015-07-02 3:07 ` Tejun Heo
2015-07-03 22:12 ` [PATCH block/for-4.3] writeback: remove wb_writeback_work->single_wait/done Tejun Heo
2015-07-08 8:24 ` Jan Kara
2015-05-22 21:14 ` [PATCH 46/51] writeback: restructure try_writeback_inodes_sb[_nr]() Tejun Heo
2015-05-22 21:14 ` [PATCH 47/51] writeback: make writeback initiation functions handle multiple bdi_writeback's Tejun Heo
2015-05-22 21:14 ` [PATCH 48/51] writeback: dirty inodes against their matching cgroup bdi_writeback's Tejun Heo
[not found] ` <1432329245-5844-49-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2015-07-01 19:16 ` Jan Kara
2015-05-22 21:14 ` [PATCH 49/51] buffer, writeback: make __block_write_full_page() honor cgroup writeback Tejun Heo
2015-07-01 19:21 ` Jan Kara
[not found] ` <20150701192102.GK7252-+0h/O2h83AeN3ZZ/Hiejyg@public.gmane.org>
2015-07-01 19:28 ` Jan Kara
2015-05-22 21:14 ` [PATCH 50/51] mpage: make __mpage_writepage() " Tejun Heo
2015-07-01 19:26 ` Jan Kara
2015-05-22 21:14 ` [PATCH 51/51] ext2: enable cgroup writeback support Tejun Heo
2015-07-01 19:29 ` Jan Kara
2015-07-02 3:08 ` Tejun Heo
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