linux-kernel - Re: [PATCH]vmscan: handle underflow for get_scan

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: <20100412015739.GA14988@sli10-desk.sh.intel.com>
Date:	Mon, 12 Apr 2010 09:57:39 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Wu, Fengguang" <fengguang.wu@...el.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"riel@...hat.com" <riel@...hat.com>
Subject: Re: [PATCH]vmscan: handle underflow for get_scan_ratio

On Sat, Apr 10, 2010 at 05:20:57AM +0800, Andrew Morton wrote:
> On Fri, 9 Apr 2010 14:51:04 +0800
> Shaohua Li <shaohua.li@...el.com> wrote:
> 
> > get_scan_ratio() calculates percentage and if the percentage is < 1%, it will
> > round percentage down to 0% and cause we completely ignore scanning anon/file
> > pages to reclaim memory even the total anon/file pages are very big.
> > 
> > To avoid underflow, we don't use percentage, instead we directly calculate
> > how many pages should be scaned. In this way, we should get several scanned pages
> > for < 1% percent.
> > 
> > This has some benefits:
> > 1. increase our calculation precision
> > 2. making our scan more smoothly. Without this, if percent[x] is underflow,
> > shrink_zone() doesn't scan any pages and suddenly it scans all pages when priority
> > is zero. With this, even priority isn't zero, shrink_zone() gets chance to scan
> > some pages.
> > 
> > Note, this patch doesn't really change logics, but just increase precision. For
> > system with a lot of memory, this might slightly changes behavior. For example,
> > in a sequential file read workload, without the patch, we don't swap any anon
> > pages. With it, if anon memory size is bigger than 16G, we will see one anon page
> > swapped. The 16G is calculated as PAGE_SIZE * priority(4096) * (fp/ap). fp/ap
> > is assumed to be 1024 which is common in this workload. So the impact sounds not
> > a big deal.
> 
> I grabbed this.
> 
> Did we decide that this needed to be backported into 2.6.33.x?  If so,
> some words explaining the reasoning would be needed.
> 
> Come to that, it's not obvious that we need this in 2.6.34 either. 
Not needed.

> is the user-visible impact here?
Should be very small I think.

Thanks,
Shaohua
--
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/