linux-kernel - Re: [PATCH] Hugepages should be accounted as unevictable pages.

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Message-Id: <20090623135017.220D.A69D9226@jp.fujitsu.com>
Date:	Tue, 23 Jun 2009 14:05:47 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	akataria@...are.com
Cc:	kosaki.motohiro@...fujitsu.com,
	LKML <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Mel Gorman <mel@....ul.ie>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] Hugepages should be accounted as unevictable pages.

> > > Unevictable:           0 kB
> > > Mlocked:               0 kB
> > > HugePages_Total:      20
> > > HugePages_Free:       20
> > > HugePages_Rsvd:        0
> > > HugePages_Surp:        0
> > > 
> > > After the patch:
> > > 
> > > Unevictable:       81920 kB
> > > Mlocked:               0 kB
> > > HugePages_Total:      20
> > > HugePages_Free:       20
> > > HugePages_Rsvd:        0
> > > HugePages_Surp:        0
> > 
> > At first, We should clarify the spec of unevictable.
> > Currently, Unevictable field mean the number of pages in unevictable-lru
> > and hugepage never insert any lru.
> > 
> > I think this patch will change this rule.
> 
> I agree, and that's why I added a comment to the documentation file to
> that effect. If you think its not explicit or doesn't explain what its
> supposed to we can add something more there.
> 
> IMO, the proc output should give the total number of unevictable pages
> in the system and, since hugepages are also in fact unevictable so I
> don't see a reason why they shouldn't be accounted accordingly.
> What do you think ? 

ummm...

I'm not sure this unevictable definition is good idea or not. currently
hugepage isn't only non-account memory, but also various kernel memory doesn't
account.

one of drawback is that zone_page_state(UNEVICTABLE) lost to mean #-of-unevictable-pages.
e.g.  following patch is wrong?

fs/proc/meminfo.c meminfo_proc_show()
----------------------------
-                K(pages[LRU_UNEVICTABLE]),
+                K(pages[LRU_UNEVICTABLE]) + hstate->nr_huge_pages,


Plus, I didn't find any practical benefit in this patch. do you have it?
or You only want to natural definition?

I don't have any strong oppose reason, but I also don't have any strong
agree reason.


Lee, What do you think?




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