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Sun, 06 Sep 2026 11:03:27 +0000 (GMT) Received: from smtpav05.dal12v.mail.ibm.com (smtpav05.dal12v.mail.ibm.com [10.241.53.104]) by smtprelay07.wdc07v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 686B3Q7m15991378 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sun, 6 Sep 2026 11:03:26 GMT Received: from smtpav05.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 844055806E; Sun, 6 Sep 2026 11:03:26 +0000 (GMT) Received: from smtpav05.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 053E55806C; Sun, 6 Sep 2026 11:03:11 +0000 (GMT) Received: from [9.61.37.159] (unknown [9.61.37.159]) by smtpav05.dal12v.mail.ibm.com (Postfix) with ESMTP; Sun, 6 Sep 2026 11:03:10 +0000 (GMT) Message-ID: <350d1460-4650-4964-8795-aa67c5517dc3@linux.ibm.com> Date: Sun, 6 Sep 2026 16:33:09 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] blk-cgroup: use a request_queue rhashtable for blkg lookup To: Yu Kuai , Jens Axboe , Tejun Heo , Josef Bacik , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= Cc: Yu Kuai , Christoph Hellwig , Tao Cui , Jan Kara , Jonathan Corbet , Shuah Khan , Coly Li , Kent Overstreet , Alasdair Kergon , Mike Snitzer , Mikulas Patocka , Benjamin Marzinski , Song Liu , Li Nan , Xiao Ni , Pankaj Gupta , Dan Williams , Vishal Verma , Dave Jiang , Alison Schofield , Ira Weiny , Andreas Gruenbacher , Matthew Wilcox , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Youngjun Park , cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-bcache@vger.kernel.org, dm-devel@lists.linux.dev, linux-raid@vger.kernel.org, nvdimm@lists.linux.dev, virtualization@lists.linux.dev, gfs2@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org References: <20260823133045.970199-1-yukuai@kernel.org> <20260823133045.970199-2-yukuai@kernel.org> Content-Language: en-US From: Nilay Shroff In-Reply-To: <20260823133045.970199-2-yukuai@kernel.org> Content-Type: text/plain; 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This spreads the queue-local > blkcg association index across every blkcg and requires radix-tree > preloading before creating a blkg while holding q->queue_lock. > > Replace the radix tree and lookup hint with a request_queue-owned > rhashtable keyed by the blkcg CSS ID. Cache the ID in each blkg; the blkg > holds a CSS reference until after it leaves the hash, so the ID cannot be > reused while it is hash-visible. The integer key also reduces hashing and > comparison work relative to a pointer-sized key on 64-bit systems. > > Keep entries until blkg_release() and provide blkg_lookup_any() for callers > which need to find dying entries. blkg_lookup() filters offline entries so > existing lookup semantics remain unchanged. > > Keep q->blkg_list for ordered policy and scheduler walks. All current > walkers are cgroupfs or sysfs slow paths, so they can move to rhashtable > iteration once the q->queue_lock to q->blkcg_mutex conversion lands. > Initialize and destroy the hash with request_queue, and remove the > radix-tree preload paths which are no longer needed. > > blkg_release() removes the hash entry only when the blkg was successfully > inserted into q->blkg_list; the list_empty case covers allocation or > creation failure before insertion. > > Signed-off-by: Yu Kuai > Reviewed-by: Christoph Hellwig Looks good to me. Reviewed-by: Nilay Shroff