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Date: Mon, 12 Apr 2010 22:42:51 -0400 From: Rik van Riel <riel@...hat.com> To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> CC: Andrew Morton <akpm@...ux-foundation.org>, Shaohua Li <shaohua.li@...el.com>, "Wu, Fengguang" <fengguang.wu@...el.com>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH]vmscan: handle underflow for get_scan_ratio On 04/12/2010 09:30 PM, KOSAKI Motohiro wrote: >> On 04/09/2010 05:20 PM, Andrew Morton wrote: >> >>> Come to that, it's not obvious that we need this in 2.6.34 either. What >>> is the user-visible impact here? >> >> I suspect very little impact, especially during workloads >> where we can just reclaim clean page cache at DEF_PRIORITY. >> FWIW, the patch looks good to me, so: >> >> Acked-by: Rik van Riel<riel@...hat.com> >> > > I'm surprised this ack a bit. Rik, do you have any improvement plan about > streaming io detection logic? > I think the patch have a slightly marginal benefit, it help to<1% scan > ratio case. but it have big regression, it cause streaming io (e.g. backup > operation) makes tons swap. How? From the description I believe it took 16GB in a zone before we start scanning anon pages when reclaiming at DEF_PRIORITY? Would that casue a problem? > So, I thought we sould do either, > 1) drop this one > 2) merge to change stream io detection logic improvement at first, and > merge this one at second. We may need better streaming IO detection, anyway. I have noticed that while heavy sequential reads are fine, the virtual machines on my desktop system do a lot of whole block writes. Presumably, a lot of those writes are to the same blocks, over and over again. This causes the blocks to be promoted to the active file list, which ends up growing the active file list to the point where things from the working set get evicted. All for file pages that may only get WRITTEN to by the guests, because the guests cache their own copy whenever they need to read them! I'll have to check the page cache code to see if it keeps frequently written pages as accessed. We may be better off evicting frequently written pages, and keeping our cache space for data that is read... -- 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/
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