linux-kernel - Re: [PATCH] memcg: handle shmem's swap cache (Was 2.6.26-rc8-mm1

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 5 Jul 2008 15:11:46 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	"hugh@...itas.com" <hugh@...itas.com>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"yamamoto@...inux.co.jp" <yamamoto@...inux.co.jp>
Subject: Re: [PATCH] memcg: handle shmem's swap cache (Was 2.6.26-rc8-mm1

On Sat, 05 Jul 2008 11:11:10 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> KAMEZAWA Hiroyuki wrote:
> > My swapcache accounting under memcg patch failed to catch tmpfs(shmem)'s one.
> > Can I test this under -mm tree ?
> > (If -mm is busy, I'm not in hurry.)
> > This patch works well in my box.
> > =
> > SwapCache handling fix.
> > 
> > shmem's swapcache behavior is a little different from anonymous's one and
> > memcg failed to handle it. This patch tries to fix it.
> > 
> > After this:
> > 
> > Any page marked as SwapCache is not uncharged. (delelte_from_swap_cache()
> > delete the SwapCache flag.)
> > 
> > To check a shmem-page-cache is alive or not we use
> >  page->mapping && !PageAnon(page) instead of
> >  pc->flags & PAGE_CGROUP_FLAG_CACHE.
> > 
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> Though I am not opposed to this, I do sit up and think if keeping the reference
> count around could avoid this complexity and from my point, the maintenance
> overhead of this logic/code (I fear there might be more special cases :( )

yes, to me. but we have to fix..

But I don't like old code's refcnt handling which does
   - increment
     - does this increment was really neccesary ?
       No? ok, decrement it again.

This was much more complex to me than current code.

And old ones will needs the check at treating swap-cache. (it couldn't but if we want)

> 
> The trade-off is complexity versus the overhead of reference counting.
> 
refcnt was also very complex ;)

Thanks,
-Kame

> -- 
> 	Warm Regards,
> 	Balbir Singh
> 	Linux Technology Center
> 	IBM, ISTL
> 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/