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Date: Tue, 4 Aug 2026 17:47:21 +0200
From: Christoph Hellwig <hch@lst.de>
To: yu kuai <yukuai@fygo.io>
Cc: Christoph Hellwig <hch@lst.de>, Tao Cui <cui.tao@linux.dev>,
	Yu Kuai <yukuai@kernel.org>, Jens Axboe <axboe@kernel.dk>,
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Subject: Re: [RFC PATCH v1 2/3] blk-cgroup: store blkcg in bio instead of
 blkg
Message-ID: <20260804154721.GA11379@lst.de>
References: <20260804065313.2092022-1-yukuai@kernel.org> <20260804065313.2092022-3-yukuai@kernel.org> <a677f581-344b-4d99-846d-a00801e26033@linux.dev> <20260804133208.GB8078@lst.de> <0fc5dd22-7a8d-43f0-8555-d2ca966efff6@fygo.io>
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On Tue, Aug 04, 2026 at 11:30:55PM +0800, yu kuai wrote:
> The problem here is that remove a cgroup can also remove the blkg from radix tree,
> even through it still has active refcounts. I think this can be fixed by checking
> the cgroup online_pin first, if it's zero, we can search the blkg from the
> request_queue blkg list, where blkg will not be removed until blkg_free_workfn().
> What's better, if we can convert the blkg list to hash table with key as blk-cgroup,
> it will be much better as we can lookup from this table instead of blkcg radix tree.

Yes, I think you can really easily do that with the rhashtable.