linux-kernel - Re: [PATCH 01/10] cgroups: Add res_counter_write

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Date:	Tue, 11 Oct 2011 15:44:58 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Menage <paul@...lmenage.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>,
	Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH 01/10] cgroups: Add res_counter_write_u64() API

On Tue, Oct 04, 2011 at 03:17:51AM +0300, Kirill A. Shutemov wrote:
> On Mon, Oct 03, 2011 at 09:07:03PM +0200, Frederic Weisbecker wrote:
> > Extend the resource counter API with a mirror of
> > res_counter_read_u64() to make it handy to update a resource
> > counter value from a cgroup subsystem u64 value file.
> > 
> > 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>
> > Cc: Kirill A. Shutemov <kirill@...temov.name>
> > Cc: Containers <containers@...ts.linux-foundation.org>
> > ---
> >  include/linux/res_counter.h |    2 ++
> >  kernel/res_counter.c        |   25 +++++++++++++++++++------
> >  2 files changed, 21 insertions(+), 6 deletions(-)
> > 
> > diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
> > index c9d625c..1b3fe05 100644
> > --- a/include/linux/res_counter.h
> > +++ b/include/linux/res_counter.h
> > @@ -82,6 +82,8 @@ int res_counter_memparse_write_strategy(const char *buf,
> >  int res_counter_write(struct res_counter *counter, int member,
> >  		      const char *buffer, write_strategy_fn write_strategy);
> >  
> > +void res_counter_write_u64(struct res_counter *counter, int member, u64 val);
> > +
> >  /*
> >   * the field descriptors. one for each member of res_counter
> >   */
> > diff --git a/kernel/res_counter.c b/kernel/res_counter.c
> > index 34683ef..0faafcc 100644
> > --- a/kernel/res_counter.c
> > +++ b/kernel/res_counter.c
> > @@ -168,12 +168,26 @@ int res_counter_memparse_write_strategy(const char *buf,
> >  	return 0;
> >  }
> >  
> > +void res_counter_write_u64(struct res_counter *counter, int member, u64 val)
> > +{
> > +	unsigned long long *target;
> > +	unsigned long flags;
> > +
> > +	/*
> > +	 * We need the lock to protect against concurrent add/dec on 32 bits.
> > +	 * No need to ifdef it's seldom used.
> > +	 */
> 
> Should we hace two version of res_counter_write_u64() for 32/64 bit host?
> As with res_counter_read_u64().

I thought about it yeah.

But this is used in rare cases when the user writes the value from the cgroup
filesystem. In pratice the overhead won't be noticed.
I fear that would rather uglify the code with more ifdeffery.
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