linux-kernel - Re: [PATCH 2/4] kernfs: make kernfs_path*() behave in the style of strlcpy()

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Message-ID: <20160809195813.GF4906@mtj.duckdns.org>
Date:	Tue, 9 Aug 2016 15:58:13 -0400
From:	Tejun Heo <tj@...nel.org>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	gregkh@...uxfoundation.org, serge.hallyn@...ntu.com,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	kernel-team@...com, hannes@...xchg.org, lizefan@...wei.com
Subject: Re: [PATCH 2/4] kernfs: make kernfs_path*() behave in the style of
 strlcpy()

Hello, Serge.

On Tue, Aug 09, 2016 at 10:33:05AM -0500, Serge E. Hallyn wrote:
> > +	for (i = depth_to - 1; i >= 0; i--) {
> > +		for (kn = kn_to, j = 0; j < i; j++)
> > +			kn = kn->parent;
> 
> This is O(n^2) where n is the path depth.  It's not a hot path, though, do
> we care?

I don't think it matters.  It's a slow path and cgroup hierarchies
aren't supposed to be super deep to begin with.  If it ever does, we
can replace the cgroup->ancestor_ids[] array with ancestor pointer
array and walk that instead.

Thanks.

-- 
tejun