On Mon, Jan 02, 2012 at 12:47:03PM -0800, Don Lewis wrote: > On 2 Jan, Florian Smeets wrote: > > On 29.12.11 01:04, Kirk McKusick wrote: > >> Rather than changing BKVASIZE, I would try running the cvs2svn > >> conversion on a 16K/2K filesystem and see if that sorts out the > >> problem. If it does, it tells us that doubling the main block > >> size and reducing the number of buffers by half is the problem. > >> If that is the problem, then we will have to increase the KVM > >> allocated to the buffer cache. > >> > > > > 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. r228838 allows the system to skip 50-70% of the code when initiating a write of the UFS file page, due to async clustering. The system has to maintain 75% less amount of writes in progress.
> I think that ls is hanging because it's stumbling across the vnode that > the syncer has locked. This is the only reasonable explanation. Low-tech profile is to periodically break out into ddb and do backtrace for the syncer thread. More advanced techniques is to use dtrace or normal profiling.
pgpqweDffT9HY.pgp
Description: PGP signature
