On Thursday 01 April 2010 01:12:54 Dave Chinner wrote: > On Wed, Mar 31, 2010 at 07:07:31PM +0300, Denys Fedorysychenko wrote: > > I have a proxy server with "loaded" squid. On some moment i did sync, and > > expecting it to finish in reasonable time. Waited more than 30 minutes, > > still "sync". Can be reproduced easily. > > > > Here is some stats and info: > > > > Linux SUPERPROXY 2.6.33.1-build-0051 #16 SMP Wed Mar 31 17:23:28 EEST > > 2010 i686 GNU/Linux > > > > SUPERPROXY ~ # iostat -k -x -d 30 > > Linux 2.6.33.1-build-0051 (SUPERPROXY) 03/31/10 _i686_ (4 CPU) > > > > Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s > > avgrq-sz avgqu-sz await svctm %util > > sda 0.16 0.01 0.08 0.03 3.62 1.33 > > 88.94 0.15 1389.89 59.15 0.66 > > sdb 4.14 61.25 6.22 25.55 44.52 347.21 > > 24.66 2.24 70.60 2.36 7.49 > > sdc 4.37 421.28 9.95 98.31 318.27 2081.95 > > 44.34 20.93 193.21 2.31 24.96 > > sdd 2.34 339.90 3.97 117.47 95.48 1829.52 > > 31.70 1.73 14.23 8.09 98.20 > > ^^^^ ^^^^^ > > /dev/sdd is IO bound doing small random writeback IO. A service time > of 8ms implies that it is doing lots of large seeks. If you've got > GBs of data to sync and that's the writeback pattern, then sync will > most definitely take a long, long time. > > it may be that ext4 is allocating blocks far apart rather than close > together (as appears to be the case for /dev/sdc), so maybe this is > is related to how the filesytems are aging or how full they are... Thats correct, it is quite busy cache server. Well, if i stop squid(cache) sync will finish enough fast. If i don't - it took more than hour. Actually i left that PC after 1 hour, and it didn't finish yet. I don't think it is normal. Probably sync taking new data and trying to flush it too, and till he finish that, more data comes. Actually all what i need - to sync config directory. I cannot use fsync, because it is multiple files opened before by other processes, and sync is doing trick like this. I got dead process, and only fast way to recover system - kill the cache process, so I/O pumping will stop for a while, and sync() will have chance to finish. Sure there is way just to "remount" config partition to ro, but i guess just sync must flush only current buffer cache pages. I will do more tests now and will give exact numbers, how much time it needs with running squid and if i kill it shortly after running sync. > > Cheers, > > Dave. > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
