linux-kernel - Re: [PATCH 3/3] [RFC] tmpfs: Add FALLOC_FL_MARK_VOLATILE/UNMARK

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]

Message-ID: <4FD1848B.7040102@gmail.com>
Date:	Fri, 08 Jun 2012 00:50:19 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	John Stultz <john.stultz@...aro.org>
CC:	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Robert Love <rlove@...gle.com>, Mel Gorman <mel@....ul.ie>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Dave Chinner <david@...morbit.com>, Neil Brown <neilb@...e.de>,
	Andrea Righi <andrea@...terlinux.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Taras Glek <tgek@...illa.com>, Mike Hommey <mh@...ndium.org>,
	Jan Kara <jack@...e.cz>
Subject: Re: [PATCH 3/3] [RFC] tmpfs: Add FALLOC_FL_MARK_VOLATILE/UNMARK_VOLATILE
 handlers

(6/7/12 11:03 PM), John Stultz wrote:
> On 06/07/2012 04:41 PM, Dave Hansen wrote:
>> On 06/07/2012 03:55 AM, Dmitry Adamushko wrote:
>>> but maybe we should also purge them before we swap out some non-tmpfs
>>> pages or drop some file-backed pages?
>>
>> Sure... I guess we could kick that from either direct reclaim or from
>> kswapd. But, then we're basically back to the places where
>> shrink_slab() is called.
>>
>> I think that means that we think it's preferable to integrate this more
>> directly in the VM instead of sticking it off in the corner of tmpfs
>> only, or pretending it's a slab.
>>
>> Dunno... The slab shrinker one isn't looking _so_ bad at the moment.
>
> Dave also pointed out to me on irc that on a system without swap,
>shmem_writepage doesn't even get called, which kills the utility of
>triggering volatile purging from writepage.

Ah, right you are. swap-less system never try to reclaim anon pages. So,
volatile pages is no longer swap backed. swap backed lru is no longer suitable
place.

  
> So I'm falling back to using a shrinker for now, but I think Dmitry's
>point is an interesting one, and am interested in finding a better
>place to trigger purging volatile ranges from the mm code. If anyone has any
>suggestions, let me know, otherwise I'll go back to trying to better grok the mm code.

I hate vm feature to abuse shrink_slab(). because of, it was not designed generic callback.
it was designed for shrinking filesystem metadata. Therefore, vm keeping a balance between
page scanning and slab scanning. then, a lot of shrink_slab misuse may lead to break balancing
logic. i.e. drop icache/dcache too many and makes perfomance impact.

As far as a code impact is small, I'm prefer to connect w/ vm reclaim code directly.
--
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/