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Date: Fri, 14 Aug 2026 10:15:31 +0200
From: Christoph Hellwig <hch@lst.de>
To: yukuai@fygo.io
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Subject: Re: [RFC PATCH v2 2/4] blk-cgroup: use a request_queue rhashtable
 for blkg lookup
Message-ID: <20260814081531.GA13546@lst.de>
References: <20260811064744.1139446-1-yukuai@kernel.org> <20260811064744.1139446-3-yukuai@kernel.org> <20260814071232.GA9784@lst.de> <f7350050-062a-4ced-9396-05ac33ac3e60@fnnas.com>
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On Fri, Aug 14, 2026 at 03:50:04PM +0800, Yu Kuai wrote:
> > Are these fast path operations?  Otherwise we can walk all rhashtable
> > entries without an extra list, but it might be slower.
> 
> All users are from sysfs/cgroupfs API, I think they can be considered slow path,
> however currently spinlock is held in these procedures, I think it's better to
> convert them to blkg_lookup based iterate after spinlock is converted to the
> blkcg_mutex.

Sounds good.  Maybe put that into the commit log?

> > Please add must_hold and/or lockdep annotations for this instead of just
> > a comment.
> >
> > Also maybe mention that this does not acquire a reference and the caller
> > must already hold one?
> 
> Perhaps it's more accurate that the blkg is pinned by IO or caller already
> hold one?

Sounds good.