linux-kernel - Re: [RFC 1/5] memcg: cleanup charge routines

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Message-ID: <20140203132001.GE2495@dhcp22.suse.cz>
Date:	Mon, 3 Feb 2014 14:20:01 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [RFC 1/5] memcg: cleanup charge routines

On Thu 30-01-14 12:18:37, Johannes Weiner wrote:
> On Tue, Dec 17, 2013 at 04:45:26PM +0100, Michal Hocko wrote:
[...]
> > -static int __mem_cgroup_try_charge(struct mm_struct *mm,
> > -				   gfp_t gfp_mask,
> > +static int __mem_cgroup_try_charge_memcg(gfp_t gfp_mask,
> >  				   unsigned int nr_pages,
> > -				   struct mem_cgroup **ptr,
> > +				   struct mem_cgroup *memcg,
> >  				   bool oom)
> 
> Why not keep the __mem_cgroup_try_charge() name?  It's shorter and
> just as descriptive.

I wanted to have 2 different names with clear reference to _what_ is
going to be charged. But I am always open to naming suggestions.

[...]
> > +static bool mem_cgroup_bypass_charge(void)
> 
> The name and parameter list suggests this consults some global memory
> cgroup state.  current_bypass_charge()?

OK, that sounds better.

> I think ultimately we want to move away from all these mem_cgroup
> prefixes of static functions in there, they add nothing of value.

Yes, I agree that mem_cgroup prefix is clumsy and we should drop it.

[...]
> > +/*
> > + * Charges and returns memcg associated with the given mm (or root_mem_cgroup
> > + * if mm is NULL). Returns NULL if memcg is under OOM.
> > + */
> > +static struct mem_cgroup *mem_cgroup_try_charge_mm(struct mm_struct *mm,
> > +				   gfp_t gfp_mask,
> > +				   unsigned int nr_pages,
> > +				   bool oom)
> 
> We already have a try_get_mem_cgroup_from_mm().
>
> After this series, this function basically duplicates that and it
> would be much cleaner if we only had one try_charge() function and let
> all the callers use the appropriate try_get_mem_cgroup_from_wherever()
> themselves.

try_get_mem_cgroup_from_mm doesn't charge memory itself. It just tries
to get memcg from the given mm. It is called also from a context which
doesn't charge any memory (task_in_mem_cgroup). Or have I misunderstood
you?

> If you pull the patch that moves consume_stock() back into
> try_charge() up front, I think this cleanup would be more obvious and
> the result even better.

OK, I can move it.

Thanks!

-- 
Michal Hocko
SUSE Labs
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