Re: Peculiar...

From: Michael O'Reilly <michael@dont-contact.us>
Date: Tue, 17 Feb 1998 16:47:01 +0800

In message <Pine.LNX.3.96dg4.980217004106.3454C-100000@twinlark.arctic.org>, De
an Gaudet writes:
> > > access times on inodes being flushed back to disk?
> >
> > Always 3 seconds? at irregular intervals? The object is hot, it should
> > be being served out of memory... (compiled with --enable-async-io)
>
> It may be reading it from memory, but depending on what unix this is it
> may also be flushing that inode rather fast. In particular if it's a busy
> proxy then it may have reach some internal limit that says "flush inodes
> if we have THIS many dirty".
 
> If it's recent linux or freebsd then try mounting your cache disk with
> noatime. I doubt you'll miss uptodate atimes...

Already done. Disk I/O is at a premium already. :)
 
> Just a guess. Usually this shows up at 30s intervals though (ISTR it
> being shorter on IRIX... haven't dealt with it in a long time).

On linux, the daemon wakes up every 5 seconds, and flushes a
percentage of the dirty blocks.

Doing a 'vmstat 1' producing a nigh regular write every 5
seconds. Which doesn't correlate with the pauses. :(

# vmstat 1
 procs memory swap io system cpu
 r b w swpd free buff cache si so bi bo in cs us sy id
 2 0 0 0 6344 84740 52076 0 0 43 0 2402 1031 33 59 8
 2 0 0 0 6464 84716 52048 0 0 21 0 2201 799 25 64 10
 4 1 0 0 6508 84692 52072 0 0 54 1131 2973 1746 31 66 3
 2 0 0 0 6632 84688 52036 0 0 30 238 2494 1016 34 50 16
 3 1 0 0 6712 84672 52016 0 0 21 0 2439 856 22 75 3
 1 0 0 0 6732 84644 52088 0 0 128 0 2744 1101 41 52 7
 2 0 0 0 6780 84608 52096 0 0 53 0 2515 988 37 57 7
 4 5 0 0 6880 84584 52060 0 0 18 494 2472 970 32 57 11
 3 1 0 0 6844 84572 52136 0 0 142 804 2753 1345 42 54 4
 1 0 0 0 6992 84544 52196 0 0 105 0 2359 805 41 57 3
 4 0 0 0 6864 84520 52336 0 0 193 0 2756 1193 40 56 5
 2 0 0 0 6740 84500 52348 0 0 27 0 2665 1056 28 69 3
 4 0 0 0 6848 84492 52316 0 0 25 0 2599 1140 40 58 2
 3 4 0 0 6696 84456 52388 0 0 110 1264 3187 1374 32 67 1
 2 0 0 0 6428 84432 52500 0 0 167 31 2861 1177 43 56 1
Received on Tue Jul 29 2003 - 13:15:46 MDT

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