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Date: Thu, 9 Jul 2026 08:18:37 +0200
From: Christoph Hellwig <hch@lst.de>
To: Yu Kuai <yukuai@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>,
	Christoph Hellwig <hch@lst.de>, Keith Busch <kbusch@kernel.org>,
	Sagi Grimberg <sagi@grimberg.me>, Alasdair Kergon <agk@redhat.com>,
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	Mike Snitzer <snitzer@kernel.org>,
	Mikulas Patocka <mpatocka@redhat.com>,
	Dongsheng Yang <dongsheng.yang@linux.dev>,
	Zheng Gu <cengku@gmail.com>, Coly Li <colyli@fygo.io>,
	Kent Overstreet <kent.overstreet@linux.dev>,
	Josef Bacik <josef@toxicpanda.com>, Yu Kuai <yukuai@fygo.io>,
	Nilay Shroff <nilay@linux.ibm.com>, linux-block@vger.kernel.org,
	cgroups@vger.kernel.org, linux-nvme@lists.infradead.org,
	dm-devel@lists.linux.dev, linux-bcache@vger.kernel.org
Subject: Re: [RFC PATCH v1 15/17] blk-cgroup: remove blkg radix tree
 preloading
Message-ID: <20260709061837.GF16504@lst.de>
References: <20260704195124.1375075-1-yukuai@kernel.org> <20260704195124.1375075-16-yukuai@kernel.org>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Sun, Jul 05, 2026 at 03:51:22AM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai@fygo.io>
> 
> blkg creation is now serialized by q->blkcg_mutex and no longer runs
> under q->queue_lock.  The radix tree is initialized with GFP_NOWAIT, so
> radix_tree_insert() cannot sleep while blkcg->lock is held and the old
> preload dance is no longer needed.
> 
> Remove the preload calls and the associated unwind path.

Isn't the GFP_NOWAIT a bit of a problem because it can fail way too
easy?

What about converting both the radix tree and list to an xarray
using the internal xarray to deal with sleeping allocations?