From: Dennis Zhou <dennisszhou@gmail.com>
To: Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Josef Bacik <josef@toxicpanda.com>
Cc: kernel-team@fb.com, linux-block@vger.kernel.org,
cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
"Dennis Zhou (Facebook)" <dennisszhou@gmail.com>
Subject: [PATCH 03/12] blkcg: convert blkg_lookup_create to find closest blkg
Date: Thu, 6 Sep 2018 17:10:36 -0400 [thread overview]
Message-ID: <20180906211045.29055-4-dennisszhou@gmail.com> (raw)
In-Reply-To: <20180906211045.29055-1-dennisszhou@gmail.com>
From: "Dennis Zhou (Facebook)" <dennisszhou@gmail.com>
There are several scenarios where blkg_lookup_create can fail. Examples
include the blkcg dying, request_queue is dying, or simply being OOM. At
the end of the day, most handle this by simply falling back to the
q->root_blkg and calling it a day.
This patch implements the notion of closest blkg. During
blkg_lookup_create, if it fails to create, return the closest blkg
found or the q->root_blkg. blkg_try_get_closest is introduced and used
during association so a bio is always attached to a blkg.
Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
---
block/bio.c | 4 +---
block/blk-cgroup.c | 22 +++++++++++++++-------
include/linux/blk-cgroup.h | 14 ++++++++++++++
3 files changed, 30 insertions(+), 10 deletions(-)
diff --git a/block/bio.c b/block/bio.c
index 91c6b1458454..cd947ad4cf08 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -2021,9 +2021,7 @@ int bio_associate_blkg(struct bio *bio, struct blkcg_gq *blkg)
{
if (unlikely(bio->bi_blkg))
return -EBUSY;
- if (!blkg_try_get(blkg))
- return -ENODEV;
- bio->bi_blkg = blkg;
+ bio->bi_blkg = blkg_try_get_closest(blkg);
return 0;
}
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index cd0d97bed83d..9f8aba29b7c1 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -268,9 +268,8 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
* that all non-root blkg's have access to the parent blkg. This function
* should be called under RCU read lock and @q->queue_lock.
*
- * Returns pointer to the looked up or created blkg on success, ERR_PTR()
- * value on error. If @q is dead, returns ERR_PTR(-EINVAL). If @q is not
- * dead and bypassing, returns ERR_PTR(-EBUSY).
+ * Returns the blkg or the closest blkg if blkg_create fails as it walks
+ * down from root.
*/
struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
struct request_queue *q)
@@ -285,7 +284,7 @@ struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
* we shouldn't allow anything to go through for a bypassing queue.
*/
if (unlikely(blk_queue_bypass(q)))
- return ERR_PTR(blk_queue_dying(q) ? -ENODEV : -EBUSY);
+ return q->root_blkg;
blkg = __blkg_lookup(blkcg, q, true);
if (blkg)
@@ -298,14 +297,23 @@ struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
while (true) {
struct blkcg *pos = blkcg;
struct blkcg *parent = blkcg_parent(blkcg);
-
- while (parent && !__blkg_lookup(parent, q, false)) {
+ struct blkcg_gq *ret_blkg = NULL;
+
+ while (parent) {
+ blkg = __blkg_lookup(parent, q, false);
+ if (blkg) {
+ /* remember closest blkg */
+ ret_blkg = blkg;
+ break;
+ }
pos = parent;
parent = blkcg_parent(parent);
}
blkg = blkg_create(pos, q, NULL);
- if (pos == blkcg || IS_ERR(blkg))
+ if (IS_ERR(blkg))
+ return ret_blkg ?: q->root_blkg;
+ if (pos == blkcg)
return blkg;
}
}
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index cc0f238530f6..1fbff1bbb651 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -549,6 +549,20 @@ static inline struct blkcg_gq *blkg_try_get(struct blkcg_gq *blkg)
return NULL;
}
+/**
+ * blkg_try_get_closest - try and get a blkg ref on the closet blkg
+ * @blkg: blkg to get
+ *
+ * This walks up the blkg tree to find the closest non-dying blkg and returns
+ * the blkg that it did association with as it may not be the passed in blkg.
+ */
+static inline struct blkcg_gq *blkg_try_get_closest(struct blkcg_gq *blkg)
+{
+ while (!atomic_inc_not_zero(&blkg->refcnt))
+ blkg = blkg->parent;
+
+ return blkg;
+}
void __blkg_release_rcu(struct rcu_head *rcu);
--
2.17.1
next prev parent reply other threads:[~2018-09-06 21:11 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-06 21:10 [PATCH 00/12] block: always associate blkg and refcount cleanup Dennis Zhou
2018-09-06 21:10 ` [PATCH 01/12] blkcg: fix ref count issue with bio_blkcg using task_css Dennis Zhou
2018-09-07 16:52 ` Tejun Heo
2018-09-06 21:10 ` [PATCH 02/12] blkcg: update blkg_lookup_create to do locking Dennis Zhou
2018-09-07 6:17 ` Liu Bo
2018-09-06 21:10 ` Dennis Zhou [this message]
2018-09-07 17:27 ` [PATCH 03/12] blkcg: convert blkg_lookup_create to find closest blkg Tejun Heo
2018-09-07 20:33 ` Dennis Zhou
2018-09-06 21:10 ` [PATCH 04/12] blkcg: always associate a bio with a blkg Dennis Zhou
2018-09-06 21:10 ` [PATCH 05/12] blkcg: consolidate bio_issue_init to be a part of core Dennis Zhou
2018-09-07 19:18 ` Liu Bo
2018-09-06 21:10 ` [PATCH 06/12] blkcg: associate a blkg for pages being evicted by swap Dennis Zhou
2018-09-06 21:10 ` [PATCH 07/12] blkcg: associate writeback bios with a blkg Dennis Zhou
2018-09-06 21:10 ` [PATCH 08/12] blkcg: remove bio->bi_css and instead use bio->bi_blkg Dennis Zhou
2018-09-06 21:10 ` [PATCH 09/12] blkcg: remove additional reference to the css Dennis Zhou
2018-09-07 17:54 ` Tejun Heo
2018-09-07 20:24 ` Dennis Zhou
2018-09-06 21:10 ` [PATCH 10/12] blkcg: cleanup and make blk_get_rl use blkg_lookup_create Dennis Zhou
2018-09-11 5:11 ` [LKP] [blkcg] 1d0e59f90b: BUG:unable_to_handle_kernel kernel test robot
2018-09-06 21:10 ` [PATCH 11/12] blkcg: change blkg reference counting to use percpu_ref Dennis Zhou
2018-09-07 17:59 ` Tejun Heo
2018-09-06 21:10 ` [PATCH 12/12] blkcg: rename blkg_try_get to blkg_tryget Dennis Zhou
2018-09-11 18:41 [PATCH v3 00/12] block: always associate blkg and refcount cleanup Dennis Zhou
2018-09-11 18:41 ` [PATCH 03/12] blkcg: convert blkg_lookup_create to find closest blkg Dennis Zhou
2018-09-11 23:50 ` Tejun Heo
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180906211045.29055-4-dennisszhou@gmail.com \
--to=dennisszhou@gmail.com \
--cc=axboe@kernel.dk \
--cc=cgroups@vger.kernel.org \
--cc=hannes@cmpxchg.org \
--cc=josef@toxicpanda.com \
--cc=kernel-team@fb.com \
--cc=linux-block@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=tj@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).