Linux-Block Archive on lore.kernel.org
 help / color / Atom feed
From: Christoph Hellwig <hch@lst.de>
To: Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>
Cc: Dennis Zhou <dennis@kernel.org>, Li Zefan <lizefan@huawei.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	dm-devel@redhat.com, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
	linux-mm@kvack.org
Subject: [PATCH 08/14] block: bypass blkg_tryget_closest for the root_blkg
Date: Sat, 27 Jun 2020 09:31:53 +0200
Message-ID: <20200627073159.2447325-9-hch@lst.de> (raw)
In-Reply-To: <20200627073159.2447325-1-hch@lst.de>

The root_blkg is only torn down at the very end of removing a queue.
So in the I/O submission path is always has a life reference and we
can just grab another one using blkg_get instead of doing a tryget
and parent walk that won't lead anywhere.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-cgroup.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 6aedb73ffbf473..0912820d4f8194 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1758,16 +1758,21 @@ void bio_associate_blkg_from_css(struct bio *bio,
 				 struct cgroup_subsys_state *css)
 {
 	struct request_queue *q = bio->bi_disk->queue;
-	struct blkcg_gq *blkg = q->root_blkg;
 
 	if (bio->bi_blkg)
 		blkg_put(bio->bi_blkg);
 
-	rcu_read_lock();
-	if (css && css->parent)
+	if (css && css->parent) {
+		struct blkcg_gq *blkg;
+
+		rcu_read_lock();
 		blkg = blkg_lookup_create(css_to_blkcg(css), q);
-	bio->bi_blkg = blkg_tryget_closest(blkg);
-	rcu_read_unlock();
+		bio->bi_blkg = blkg_tryget_closest(blkg);
+		rcu_read_unlock();
+	} else {
+		blkg_get(q->root_blkg);
+		bio->bi_blkg = q->root_blkg;
+	}
 }
 EXPORT_SYMBOL_GPL(bio_associate_blkg_from_css);
 
-- 
2.26.2


  parent reply index

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-27  7:31 drive-by blk-cgroup cleanups Christoph Hellwig
2020-06-27  7:31 ` [PATCH 01/14] dm: use bio_uninit instead of bio_disassociate_blkg Christoph Hellwig
2020-06-29  9:31   ` Johannes Thumshirn
2020-07-08 14:02   ` Mike Snitzer
2020-06-27  7:31 ` [PATCH 02/14] block: remove bio_disassociate_blkg Christoph Hellwig
2020-06-29  9:33   ` Johannes Thumshirn
2020-06-27  7:31 ` [PATCH 03/14] block: really clone the block cgroup in bio_clone_blkg_association Christoph Hellwig
2020-06-29  9:37   ` Johannes Thumshirn
2020-06-27  7:31 ` [PATCH 04/14] block: merge __bio_associate_blkg into bio_associate_blkg_from_css Christoph Hellwig
2020-06-29  9:55   ` Johannes Thumshirn
2020-06-27  7:31 ` [PATCH 05/14] block: move bio_associate_blkg_from_page to mm/page_io.c Christoph Hellwig
2020-06-29  9:59   ` Johannes Thumshirn
2020-06-29 10:08   ` Johannes Thumshirn
2020-06-27  7:31 ` [PATCH 06/14] block: move the bio cgroup associatation helpers to blk-cgroup.c Christoph Hellwig
2020-06-29 11:51   ` Johannes Thumshirn
2020-06-27  7:31 ` [PATCH 07/14] block: merge blkg_lookup_create and __blkg_lookup_create Christoph Hellwig
2020-06-29 12:21   ` Johannes Thumshirn
2020-06-27  7:31 ` Christoph Hellwig [this message]
2020-06-27  7:31 ` [PATCH 09/14] block: move the initial blkg lookup into blkg_tryget_closest Christoph Hellwig
2020-06-27  7:31 ` [PATCH 10/14] blk-cgroup: remove the !bio->bi_blkg check in blkcg_bio_issue_check Christoph Hellwig
2020-06-27  7:31 ` [PATCH 11/14] cgroup: unexport cgroup_rstat_updated Christoph Hellwig
2020-06-27  7:31 ` [PATCH 12/14] blk-cgroup: move rcu locking from blkcg_bio_issue_check to blk_throtl_bio Christoph Hellwig
2020-06-27  7:31 ` [PATCH 13/14] blk-cgroup: remove blkcg_bio_issue_check Christoph Hellwig
2020-06-27  7:31 ` [PATCH 14/14] blk-cgroup: remove a dead check in blk_throtl_bio Christoph Hellwig
2020-06-29  8:05 ` drive-by blk-cgroup cleanups Johannes Thumshirn
2020-06-29  8:08   ` Christoph Hellwig
2020-06-29  8:12     ` Johannes Thumshirn
2020-06-29 13:56 ` Tejun Heo
2020-06-29 15:09 ` Jens Axboe

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=20200627073159.2447325-9-hch@lst.de \
    --to=hch@lst.de \
    --cc=axboe@kernel.dk \
    --cc=cgroups@vger.kernel.org \
    --cc=dennis@kernel.org \
    --cc=dm-devel@redhat.com \
    --cc=hannes@cmpxchg.org \
    --cc=linux-block@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=lizefan@huawei.com \
    --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

Linux-Block Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-block/0 linux-block/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-block linux-block/ https://lore.kernel.org/linux-block \
		linux-block@vger.kernel.org
	public-inbox-index linux-block

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-block


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git