Date: Tue, 3 Jan 2012 00:02:22 -0800 (PST) From: Don Lewis <truckman@FreeBSD.org> To: flo@FreeBSD.org Cc: attilio@FreeBSD.org, current@FreeBSD.org, mckusick@mckusick.com, phk@phk.freebsd.dk, kib@FreeBSD.org, seanbru@yahoo-inc.com Subject: Re: dogfooding over in clusteradm land Message-ID: <201201030802.q0382M5a006876@gw.catspoiler.org> In-Reply-To: <201201030235.q032ZY4V006462@gw.catspoiler.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On 2 Jan, Don Lewis wrote: > On 2 Jan, Don Lewis wrote: >> On 2 Jan, Florian Smeets wrote: > >>> This does not make a difference. I tried on 32K/4K with/without journal >>> and on 16K/2K all exhibit the same problem. At some point during the >>> cvs2svn conversion the sycer starts to use 100% CPU. The whole process >>> hangs at that point sometimes for hours, from time to time it does >>> continue doing some work, but really really slow. It's usually between >>> revision 210000 and 220000, when the resulting svn file gets bigger than >>> about 11-12Gb. At that point an ls in the target dir hangs in state ufs. >>> >>> I broke into ddb and ran all commands which i thought could be useful. >>> The output is at http://tb.smeets.im/~flo/giant-ape_syncer.txt >> >> Tracing command syncer pid 9 tid 100183 td 0xfffffe00120e9000 >> cpustop_handler() at cpustop_handler+0x2b >> ipi_nmi_handler() at ipi_nmi_handler+0x50 >> trap() at trap+0x1a8 >> nmi_calltrap() at nmi_calltrap+0x8 >> --- trap 0x13, rip = 0xffffffff8082ba43, rsp = 0xffffff8000270fe0, rbp = 0xffffff88c97829a0 --- >> _mtx_assert() at _mtx_assert+0x13 >> pmap_remove_write() at pmap_remove_write+0x38 >> vm_object_page_remove_write() at vm_object_page_remove_write+0x1f >> vm_object_page_clean() at vm_object_page_clean+0x14d >> vfs_msync() at vfs_msync+0xf1 >> sync_fsync() at sync_fsync+0x12a >> sync_vnode() at sync_vnode+0x157 >> sched_sync() at sched_sync+0x1d1 >> fork_exit() at fork_exit+0x135 >> fork_trampoline() at fork_trampoline+0xe >> --- trap 0, rip = 0, rsp = 0xffffff88c9782d00, rbp = 0 --- >> >> I thinks this explains why the r228838 patch seems to help the problem. >> Instead of an application call to msync(), you're getting bitten by the >> syncer doing the equivalent. I don't know why the syncer is CPU bound, >> though. From my understanding of the patch it only optimizes the I/O. >> Without the patch, I would expect that the syncer would just spend a lot >> of time waiting on I/O. My guess is that this is actually a vm problem. >> There are nested loops in vm_object_page_clean() and >> vm_object_page_remove_write(), so you could be doing something that's >> causing lots of looping in that code. > > Does the machine recover if you suspend cvs2svn? I think what is > happening is that cvs2svn is continuing to dirty pages while the syncer > is trying to sync the file. From my limited understanding of this code, > it looks to me like every time cvs2svn dirties a page, it will trigger a > call to vm_object_set_writeable_dirty(), which will increment > object->generation. Whenever vm_object_page_clean() detects a change in > the generation count, it restarts its scan of the pages associated with > the object. This is probably not optimal ... Since the syncer is only trying to flush out pages that have been dirty for the last 30 seconds, I think that vm_object_set_writeable_dirty() should just make one pass through the object, ignoring generation, and then return when it is called from the syncer. That should keep vm_object_set_writeable_dirty() from looping over the object again and again if another process is actively dirtying the object.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201201030802.q0382M5a006876>