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Date: Wed, 24 Aug 2011 17:32:05 +0800 From: Wu Fengguang <fengguang.wu@...el.com> To: Pekka Enberg <penberg@...nel.org> Cc: Stefan Priebe - Profihost AG <s.priebe@...fihost.ag>, LKML <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org>, Mel Gorman <mel@....ul.ie>, Jens Axboe <jaxboe@...ionio.com>, Linux Netdev List <netdev@...r.kernel.org> Subject: Re: slow performance on disk/network i/o full speed after drop_caches On Wed, Aug 24, 2011 at 02:20:07PM +0800, Pekka Enberg wrote: > On Wed, Aug 24, 2011 at 9:06 AM, Stefan Priebe - Profihost AG > <s.priebe@...fihost.ag> wrote: > > i hope this is the correct list to write to if it would be nice to give me a > > hint where i can ask. > > > > Kernel: 2.6.38 > > > > I'm seeing some strange problems on some of our servers after upgrading to > > 2.6.38. > > > > I'm copying a 1GB file via scp from Machine A to Machine B. When B is > > freshly booted the file transfer is done with about 80 to 85 Mb/s. I can > > repeat that various times to performance degrease. > > > > Then after some days copying is only done with about 900kb/s up to 3Mb/s > > going up and down while transfering the file. > > > > When i then do drop_caches it works again on 80Mb/s. > > > > sync && echo 3 >/proc/sys/vm/drop_caches && sleep 2 && echo 0 > >>/proc/sys/vm/drop_caches > > > > Attached is also an output of meminfo before and after drop_caches. > > > > What's going on here? MemFree is pretty high. > > > > Please CC me i'm not on list. > > Interesting. I can imagine one or more of the following to be > involved: networking, vmscan, block, and writeback. Lets CC all of > them! > > > # before drop_caches > > > > # cat /proc/meminfo > > MemTotal: 8185544 kB > > MemFree: 6670292 kB > > Buffers: 105164 kB > > Cached: 166672 kB > > SwapCached: 0 kB > > Active: 728308 kB > > Inactive: 567428 kB > > Active(anon): 639204 kB > > Inactive(anon): 394932 kB > > Active(file): 89104 kB > > Inactive(file): 172496 kB > > Unevictable: 2976 kB > > Mlocked: 2992 kB > > SwapTotal: 1464316 kB > > SwapFree: 1464316 kB > > Dirty: 52 kB > > Writeback: 0 kB Since dirty/writeback pages are low, it seems not being throttled by balance_dirty_pages(). Stefan, would you please run this several times on the server? ps -eo user,pid,tid,class,rtprio,ni,pri,psr,pcpu,vsz,rss,pmem,stat,wchan:28,cmd | grep scp It will show where the scp task is blocked (the wchan field). Hope it helps. Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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