linux-kernel - Re: [PATCH 1/2] vmscan: shrink_slab() require number of lru

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: <20100628102342.386D.A69D9226@jp.fujitsu.com>
Date:	Mon, 28 Jun 2010 10:32:00 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 1/2] vmscan: shrink_slab() require number of lru_pages, not page order

> On Fri, 25 Jun 2010, KOSAKI Motohiro wrote:
> 
> > Fix simple argument error. Usually 'order' is very small value than
> > lru_pages. then it can makes unnecessary icache dropping.
> 
> This is going to reduce the delta that is added to shrinker->nr
> significantly thereby increasing the number of times that shrink_slab() is
> called.

Yup. But,

Smaller shrink -> only makes retry
Bigger shrink  -> makes unnecessary icache/dcache drop. it can bring
                  mysterious low performance.


> What does the "lru_pages" parameter do in shrink_slab()? Looks
> like its only role is as a divison factor in a complex calculation of
> pages to be scanned.

Yes.
scanned/lru_pages ratio define basic shrink_slab puressure strength.

So, If you intentionally need bigger slab pressure, bigger scanned parameter
passing is better rather than mysterious 'order' parameter.

> 
> do_try_to_free_pages passes 0 as "lru_pages" to shrink_slab() when trying
> to do cgroup lru scans. Why is that?

?
When cgroup lru scans, do_try_to_free_pages() don't call shrink_slab().


--
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/