linux-kernel - Re: [PATCH 06/11] cgroups: Add res counter common ancestor searching

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Date:	Sat, 1 Oct 2011 18:19:49 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Containers <containers@...ts.osdl.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Aditya Kali <adityakali@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Kay Sievers <kay.sievers@...y.org>,
	Tim Hockin <thockin@...kin.org>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 06/11] cgroups: Add res counter common ancestor searching

On Sat, Oct 01, 2011 at 05:07:03PM +0200, Frederic Weisbecker wrote:
> On Sun, Sep 18, 2011 at 10:59:32PM +0300, Kirill A. Shutemov wrote:
> > On Tue, Sep 13, 2011 at 01:11:26AM +0200, Frederic Weisbecker wrote:
> > > Add a new API to find the common ancestor between two resource
> > > counters. This includes the passed resource counter themselves.
> > > 
> > > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> > > Acked-by: Paul Menage <paul@...lmenage.org>
> > > Cc: Li Zefan <lizf@...fujitsu.com>
> > > Cc: Johannes Weiner <hannes@...xchg.org>
> > > Cc: Aditya Kali <adityakali@...gle.com>
> > > Cc: Oleg Nesterov <oleg@...hat.com>
> > > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > > Cc: Kay Sievers <kay.sievers@...y.org>
> > > Cc: Tim Hockin <thockin@...kin.org>
> > > Cc: Tejun Heo <tj@...nel.org>
> > > ---
> > >  include/linux/res_counter.h |    3 +++
> > >  kernel/res_counter.c        |   22 ++++++++++++++++++++++
> > >  2 files changed, 25 insertions(+), 0 deletions(-)
> > > 
> > > diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
> > > index de4ba29..558f39b 100644
> > > --- a/include/linux/res_counter.h
> > > +++ b/include/linux/res_counter.h
> > > @@ -147,6 +147,9 @@ static inline void res_counter_uncharge(struct res_counter *counter,
> > >  	res_counter_uncharge_until(counter, NULL, val);
> > >  }
> > >  
> > > +struct res_counter *res_counter_common_ancestor(struct res_counter *l,
> > > +						struct res_counter *r);
> > > +
> > >  /**
> > >   * res_counter_margin - calculate chargeable space of a counter
> > >   * @cnt: the counter
> > > diff --git a/kernel/res_counter.c b/kernel/res_counter.c
> > > index 0cc9c7e..22f07cc 100644
> > > --- a/kernel/res_counter.c
> > > +++ b/kernel/res_counter.c
> > > @@ -91,6 +91,28 @@ void res_counter_uncharge_until(struct res_counter *counter,
> > >  	local_irq_restore(flags);
> > >  }
> > >  
> > > +/*
> > > + * Walk through r1 and r2 parents and try to find the closest common one
> > > + * between both. If none is found, it returns NULL.
> > > + */
> > > +struct res_counter *
> > > +res_counter_common_ancestor(struct res_counter *r1, struct res_counter *r2)
> > > +{
> > > +	struct res_counter *iter;
> > > +
> > > +	while (r1) {
> > > +		iter = r2;
> > > +		while (iter) {
> > > +			if (iter == r1)
> > > +				return iter;
> > > +			iter = iter->parent;
> > > +		}
> > > +
> > > +		r1 = r1->parent;
> > > +	}
> > > +
> > > +	return NULL;
> > > +}
> > 
> > Your implementation is O(n*m).
> > 
> > What about:
> > 
> > struct res_counter *
> > res_counter_common_ancestor(struct res_counter *r1, struct res_counter *r2)
> > {
> > 	struct res_counter *iter;
> > 	int r1_depth = 0, r2_depth = 0;
> > 
> > 	for (iter = r1; iter; iter = iter->parent)
> > 		r1_depth++;
> > 	for (iter = r2; iter; iter = iter->parent)
> > 		r2_depth++;
> > 
> > 	while (r1_depth > r2_depth) {
> > 		r1 = r1->parent;
> > 		r1_depth--;
> > 	}
> > 	while (r2_depth > r1_depth) {
> > 		r2 = r2->parent;
> > 		r2_depth--;
> > 	}
> > 
> > 	while (r1 != r2) {
> > 		r1 = r1->parent;
> > 		r2 = r2->parent;
> > 	}
> > 
> > 	return r1;
> > }
> 
> While applying this (works well btw) I realize you rewrote the patch.
> 
> Can you give me your "Signed-off-by:" so that I correctly set the
> authorship and the tags that come along?

Sure.

Signed-off-by: Kirill A. Shutemov <kirill@...temov.name>

-- 
 Kirill A. Shutemov
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