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Message-ID: <20100912161507.GA5247@localhost> Date: Mon, 13 Sep 2010 00:15:07 +0800 From: Wu Fengguang <fengguang.wu@...el.com> To: linux-mm <linux-mm@...ck.org> Cc: LKML <linux-kernel@...r.kernel.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Richard Kennedy <richard@....demon.co.uk>, "Martin J. Bligh" <mbligh@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, Theodore Ts'o <tytso@....edu>, Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>, Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>, KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, Chris Mason <chris.mason@...cle.com>, Christoph Hellwig <hch@....de>, "Li, Shaohua" <shaohua.li@...el.com> Subject: Re: [PATCH 13/17] writeback: reduce per-bdi dirty threshold ramp up time On Sun, Sep 12, 2010 at 11:49:58PM +0800, Wu, Fengguang wrote: > Reduce the dampening for the control system, yielding faster > convergence. > > Currently it converges at a snail's pace for slow devices (in order of > minutes). For really fast storage, the convergence speed should be fine. > > It makes sense to make it reasonably fast for typical desktops. > > After patch, it converges in ~10 seconds for 60MB/s writes and 4GB mem. > So expect ~1s for a fast 600MB/s storage under 4GB mem, or ~4s under > 16GB mem, which looks good. > > $ while true; do grep BdiDirtyThresh /debug/bdi/8:0/stats; sleep 1; done > BdiDirtyThresh: 0 kB > BdiDirtyThresh: 118748 kB > BdiDirtyThresh: 214280 kB > BdiDirtyThresh: 303868 kB > BdiDirtyThresh: 376528 kB > BdiDirtyThresh: 411180 kB > BdiDirtyThresh: 448636 kB > BdiDirtyThresh: 472260 kB > BdiDirtyThresh: 490924 kB > BdiDirtyThresh: 499596 kB > BdiDirtyThresh: 507068 kB > ... > DirtyThresh: 530392 kB One related observation is, the task fraction may suddenly drop: dd-4323 [004] 21608.535781: balance_dirty_pages: bdi=8:0 weight=97% thresh=124863 gap=7071 dirtied=513 pause=44 bw=44677838 dd-4323 [004] 21608.579568: balance_dirty_pages: bdi=8:0 weight=97% thresh=124851 gap=7315 dirtied=513 pause=44 bw=46321077 dd-4323 [004] 21608.623586: balance_dirty_pages: bdi=8:0 weight=97% thresh=124852 gap=7156 dirtied=513 pause=44 bw=45199674 dd-4323 [000] 21608.667526: balance_dirty_pages: bdi=8:0 weight=97% thresh=124853 gap=7029 dirtied=513 pause=44 bw=44337926 dd-4323 [000] 21608.711259: balance_dirty_pages: bdi=8:0 weight=97% thresh=124842 gap=7146 dirtied=513 pause=44 bw=45074728 dd-4323 [000] 21608.755051: balance_dirty_pages: bdi=8:0 weight=97% thresh=124843 gap=6891 dirtied=513 pause=48 bw=43356794 dd-4323 [000] 21608.802953: balance_dirty_pages: bdi=8:0 weight=97% thresh=124834 gap=6722 dirtied=513 pause=48 bw=42211067 dd-4323 [000] 21608.850745: balance_dirty_pages: bdi=8:0 weight=97% thresh=124834 gap=6594 dirtied=513 pause=48 bw=41326916 dd-4323 [004] 21608.900524: balance_dirty_pages: bdi=8:0 weight=62% thresh=127735 gap=7575 dirtied=513 pause=40 bw=47863047 dd-4323 [004] 21608.990461: balance_dirty_pages: bdi=8:0 weight=22% thresh=131040 gap=8064 dirtied=513 pause=40 bw=49548668 dd-4323 [004] 21609.030239: balance_dirty_pages: bdi=8:0 weight=23% thresh=130971 gap=7739 dirtied=513 pause=44 bw=47469455 dd-4323 [004] 21609.074075: balance_dirty_pages: bdi=8:0 weight=23% thresh=130915 gap=7427 dirtied=513 pause=44 bw=45455503 dd-4323 [004] 21609.117927: balance_dirty_pages: bdi=8:0 weight=24% thresh=130849 gap=7105 dirtied=513 pause=48 bw=43394683 dd-4323 [004] 21609.165843: balance_dirty_pages: bdi=8:0 weight=25% thresh=130770 gap=6898 dirtied=513 pause=48 bw=42071194 dd-4323 [004] 21609.213769: balance_dirty_pages: bdi=8:0 weight=26% thresh=130719 gap=7103 dirtied=513 pause=48 bw=43366955 dd-4323 [004] 21609.261483: balance_dirty_pages: bdi=8:0 weight=26% thresh=130655 gap=6911 dirtied=513 pause=48 bw=42130514 ... dd-4323 [001] 21619.473748: balance_dirty_pages: bdi=8:0 weight=96% thresh=124200 gap=7656 dirtied=513 pause=36 bw=55354531 dd-4323 [000] 21619.762110: balance_dirty_pages: bdi=8:0 weight=96% thresh=124148 gap=7540 dirtied=513 pause=36 bw=54586428 dd-4323 [000] 21619.804259: balance_dirty_pages: bdi=8:0 weight=96% thresh=124145 gap=7281 dirtied=513 pause=36 bw=52772359 dd-4323 [004] 21619.840740: balance_dirty_pages: bdi=8:0 weight=96% thresh=124133 gap=7397 dirtied=513 pause=36 bw=53627516 dd-4323 [004] 21619.876600: balance_dirty_pages: bdi=8:0 weight=96% thresh=124133 gap=7493 dirtied=513 pause=36 bw=54331060 dd-4323 [004] 21619.912482: balance_dirty_pages: bdi=8:0 weight=97% thresh=124133 gap=7621 dirtied=513 pause=36 bw=55266828 dd-4323 [007] 21619.955231: balance_dirty_pages: bdi=8:0 weight=95% thresh=124242 gap=7410 dirtied=513 pause=36 bw=53695642 dd-4323 [007] 21619.992100: balance_dirty_pages: bdi=8:0 weight=95% thresh=124246 gap=7542 dirtied=513 pause=36 bw=54714918 dd-4323 [007] 21620.028048: balance_dirty_pages: bdi=8:0 weight=95% thresh=124232 gap=7656 dirtied=513 pause=36 bw=55612568 dd-4323 [007] 21620.067278: balance_dirty_pages: bdi=8:0 weight=95% thresh=124217 gap=7257 dirtied=513 pause=36 bw=52780982 dd-4323 [007] 21620.103783: balance_dirty_pages: bdi=8:0 weight=95% thresh=124219 gap=7387 dirtied=513 pause=36 bw=53787250 dd-4323 [003] 21620.143069: balance_dirty_pages: bdi=8:0 weight=84% thresh=125141 gap=7253 dirtied=513 pause=36 bw=53982296 dd-4323 [000] 21620.259771: balance_dirty_pages: bdi=8:0 weight=21% thresh=130291 gap=7955 dirtied=513 pause=36 bw=56894085 dd-4323 [004] 21620.295309: balance_dirty_pages: bdi=8:0 weight=22% thresh=130210 gap=7746 dirtied=513 pause=36 bw=55325100 dd-4323 [004] 21620.331046: balance_dirty_pages: bdi=8:0 weight=22% thresh=130145 gap=7425 dirtied=513 pause=36 bw=52955050 dd-4323 [004] 21620.367022: balance_dirty_pages: bdi=8:0 weight=23% thresh=130070 gap=7222 dirtied=513 pause=40 bw=51489214 dd-4323 [004] 21620.406877: balance_dirty_pages: bdi=8:0 weight=24% thresh=130004 gap=6900 dirtied=513 pause=40 bw=49086099 dd-4323 [004] 21620.446702: balance_dirty_pages: bdi=8:0 weight=25% thresh=129935 gap=6831 dirtied=513 pause=40 bw=48603064 dd-4323 [007] 21620.486673: balance_dirty_pages: bdi=8:0 weight=26% thresh=129873 gap=6641 dirtied=513 pause=44 bw=47142569 dd-4323 [007] 21620.530438: balance_dirty_pages: bdi=8:0 weight=26% thresh=129802 gap=6442 dirtied=513 pause=44 bw=45673274 dd-4323 [007] 21620.574312: balance_dirty_pages: bdi=8:0 weight=27% thresh=129743 gap=6415 dirtied=513 pause=44 bw=45466202 dd-4323 [007] 21620.618182: balance_dirty_pages: bdi=8:0 weight=28% thresh=129685 gap=6197 dirtied=513 pause=44 bw=43856286 I've not looked into this yet.. need to go to bed now :) Thanks, Fengguang -- 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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