linux-kernel - Re: [PATCH 0/2] memcg: mm_update_next

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Date:	Sat, 19 Apr 2014 14:23:38 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Oleg Nesterov <oleg@...hat.com>
cc:	Kelley Nielsen <kelleynnn@...il.com>, Pavel Machek <pavel@....cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Chiang <pchiang@...dia.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <bsingharora@...il.com>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	"ccross@...roid.com" <ccross@...roid.com>,
	"lizefan@...wei.com" <lizefan@...wei.com>,
	"tj@...nel.org" <tj@...nel.org>,
	"ebiederm@...ssion.com" <ebiederm@...ssion.com>,
	"guillaume@...infr.org" <guillaume@...infr.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] memcg: mm_update_next_owner() should skip kthreads

On Sat, 19 Apr 2014, Oleg Nesterov wrote:
> On 04/19, Pavel Machek wrote:
> >
> > > > Hmm. I seem to see a bug in this function, it can be fulled by use_mm,
> > > > but I am not sure this can explain the problem. I'll send a patch.
> > >
> > > Untested, please review. But it really looks "obviously wrong", and note
> > > that unuse_mm() doesn't do mm_update_next_owner(). (just in case, do not
> > > confuse it with unuse_mm() in mm/swapfile.c).
> >
> > Having two functions, one exported, one static with same name -- that
> > sounds quite evil, right?
> 
> Yes, agreed.

Doubly agreed; though it seems to have escaped causing confusion
for several years, so no great hurry to resolve it.

> 
> > mmu_context.c: * unuse_mm
> > mmu_context.c:void unuse_mm(struct mm_struct *mm)
> > mmu_context.c:EXPORT_SYMBOL_GPL(unuse_mm);
> > swapfile.c:static int unuse_mm(struct mm_struct *mm,
> 
> Yes, I was thinking about s/unuse_mm/unswap_mm/ change in swapfile.c,
> but then we should probaly rename other "unuse" functions there, and
> shmem_unuse/try_to_unuse are not static.

My preference is "swapoff" instead of "unuse" throughout there:
it saves having to explain that "unuse" implies "swapoff" each
time we send in a patch making a change to that code.

But I'd prefer you hold off for the moment: Kelley Nielsen is currently
preparing a patchset reworking try_to_unuse, and I suggested a few days
ago to include such renaming in that patchset.

Partly driven by s390's recent 45961722f8e3 "mm: add support for
discard of unused ptes" which adds further confusion with pte_unused().

Hugh
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