linux-kernel - Re: [PATCH kernfs 3/3] kernfs: switch global kernfs_pr_cont

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Message-ID: <Z_1FeW2XQTLFGGbV@slm.duckdns.org>
Date: Mon, 14 Apr 2025 07:27:21 -1000
From: Tejun Heo <tj@...nel.org>
To: alexjlzheng@...il.com
Cc: gregkh@...uxfoundation.org, alexjlzheng@...cent.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH kernfs 3/3] kernfs: switch global kernfs_pr_cont_lock to
 per-fs lock

On Sat, Apr 12, 2025 at 02:31:09AM +0800, alexjlzheng@...il.com wrote:
> From: Jinliang Zheng <alexjlzheng@...cent.com>
> 
> The kernfs implementation has big lock granularity(kernfs_pr_cont_lock) so
> every kernfs-based(e.g., sysfs, cgroup) fs are able to compete the lock.
> 
> This patch switches the global kernfs_pr_cont_lock to per-fs lock, which
> put the spinlock into kernfs_root. Of course, kernfs_pr_cont_buf also needs
> to be moved to kernfs_root.
> 
> Signed-off-by: Jinliang Zheng <alexjlzheng@...cent.com>

I don't think this one makes sense. There are lots more things that are
globally synchronizing in the printk pass. This is necessarily a really cold
path and it doesn't make anything better to split this lock.

Thanks.

-- 
tejun