linux-kernel - Re: [RFC mm][PATCH 2/5] percpu cached mm counter

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Message-Id: <20091211091114.c5fa4371.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 11 Dec 2009 09:11:14 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	minchan.kim@...il.com
Subject: Re: [RFC mm][PATCH 2/5] percpu cached mm counter

On Thu, 10 Dec 2009 19:54:59 +0100
Ingo Molnar <mingo@...e.hu> wrote:
> > [...] Exposing via perf is outside of the scope of his work.
> 
> Please make thoughts about intelligent instrumentation solutions, and 
> please think "outside of the scope" of your usual routine.
> 

I'm sorry that I don't fully understand your suggestion...

This patch is for _usage_ counters (those can increase/decrease and can be
modified in batched manner), but you don't talk about usage counter
but about lack of (useful) _event_ counters under page fault path.

If so, yes, I agree that current events are not enough.
If not, hmm ? 

More event counters I can think of around mm/page-fault is following..

  - fault to new anon pages
    + a new anon page is from remote node.
  - fault to file-backed area
    + a file page is from remote node.
  - copy_on_write
    +  a new anon page is from remote node.
    +  copy-on-write to zero page.
  - make page write (make page dirty)
  - search vma. (find_vma() is called and goes into rb-tree lookup)
  - swap-in (necessary ?)
  - get_user_page() is called to snoop other process's memory.

I wonder adding event and inserting perf_sw_event(PERF_COUNT_SW....) is
enough for adding event coutners...but is there good documentation of
this hook ?

Thanks,
-Kame

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