Re: Slight Return (was Re: [VM] 2.4.14/15-pre4 too "swap-happy"?)

[Ken Brownfield <brownfld@irridia.com>]

Just a quick followup to this, which is still a near show-stopper issue
for me.

This is easy to reproduce for me if I run updatedb locally, and then run
updatedb on a remote machine that's scanning an NFS-mounted filesystem
from the original local machine.  Instant kswapd saturation, especially
on large filesystems.

Doing updatedb on NFS-mounted filesystems also seems to cause kswapd to
peg on the NFS-client side as well.

I recently realized that slocate (at least on RH6.2 w/ 2.4 kernels) does
not seem to properly detect NFS when provided "-f nfs"...  Urgh.

Also something I noticed in slab_info (other info below):

inode_cache       369188 1027256    480 59716 128407    1 :  124   62
dentry_cache      256380 705510    128 14946 23517    1 :  252  126
buffer_head        46961  47800     96 1195 1195    1 :  252  126

That seems like a TON of {dentry,inode}_cache on a 1GB (HIMEM) machine.

I'd try 10_vm-19 but it doesn't apply cleanly for me.

Thanks for any input or ports of 10_vm-19 to 2.4.17-pre6. ;)
-- 
Ken.
brownfld@irridia.com

        total:    used:    free:  shared: buffers:  cached:
Mem:  1054011392 900526080 153485312        0 67829760 174866432
Swap: 2149548032   581632 2148966400
MemTotal:      1029308 kB
MemFree:        149888 kB
MemShared:           0 kB
Buffers:         66240 kB
Cached:         170376 kB
SwapCached:        392 kB
Active:         202008 kB
Inactive:        40380 kB
HighTotal:      131008 kB
HighFree:        30604 kB
LowTotal:       898300 kB
LowFree:        119284 kB
SwapTotal:     2099168 kB
SwapFree:      2098600 kB

Mem:  1029308K av,  886144K used,  143164K free,       0K shrd,   66240K buff
Swap: 2099168K av,     568K used, 2098600K free                  170872K cached

On Sat, Dec 01, 2001 at 07:15:02AM -0600, Ken Brownfield wrote:
| When updatedb kicked off on my 2.4.16 6-way Xeon 4GB box this morning, I
| had an unfortunate flashback:
| 
|   5:02am  up 2 days, 1 min, 59 users,  load average: 5.66, 4.86, 3.60
| 741 processes: 723 sleeping, 4 running, 0 zombie, 14 stopped
| CPU states:  0.2% user, 77.3% system,  0.0% nice, 22.3% idle
| Mem:  3351664K av, 3346504K used,    5160K free,       0K shrd,  498048K buff
| Swap: 1052248K av,  282608K used,  769640K free                 2531892K cached
| 
|   PID USER     PRI  NI  SIZE  RSS SHARE STAT  LIB %CPU %MEM   TIME COMMAND
|  2117 root      15   5   580  580   408 R N     0 99.9  0.0  17:19 updatedb
|  2635 kb        12   0  1696 1556  1216 R       0 99.9  0.0   4:16 smbd
|  2672 root      17  10  4212 4212   492 D N     0 94.7  0.1   1:39 rsync
|  2609 root       2 -20  1284 1284   672 R <     0 81.2  0.0   4:02 top
|     9 root       9   0     0    0     0 SW      0 80.7  0.0  42:50 kswapd
| 22879 kb         9   0 11548 6316  1684 S       0 11.8  0.1   7:33 smbd
| 
| Under varied load I'm not seeing the kswapd issue, but it looks like
| updatedb combined with one or two samba transfers does still reproduce
| the problem easily, and adding rsync or NFS transfers to the mix makes
| kswapd peg at 99%.
| 
| I noticed because I was trying to do kernel patches and compiles using a
| partition NFS-mounted from this machine.  I guess it sometimes pays to
| be up at 5am...
| 
| Unfortunately it's difficult for me to reboot this machine to update the
| kernel (59 users) but I will try to reproduce the problem on a separate
| machine this weekend or early next week.  And I don't have profiling on,
| so that will have to wait as well. :-(
| 
| Andrea, do you have a patch vs. 2.4.16 of your original solution to this
| problem that I could test out?  I'd rather just change one thing at a
| time rather than switching completely to an -aa kernel.
| 
| Grrrr!
| 
| Thanks much,
| -- 
| Ken.
| brownfld@irridia.com
| 
| 
| On Tue, Nov 20, 2001 at 06:50:50AM +0000, Linus Torvalds wrote:
| | In article <20011119235422.F10597@asooo.flowerfire.com>,
| | Ken Brownfield  <brownfld@irridia.com> wrote:
| | >kswapd goes up to 5-10% CPU (vs 3-6) but it finishes without issue or
| | >apparent interactivity problems.  I'm keeping it in while( 1 ), but it's
| | >been predictable so far.
| | >
| | >3-10 is a lot better than 99, but is kswapd really going to eat that
| | >much CPU in an essentially allocation-less state?
| | 
| | Well, it's obviously not allocation-less: updatedb will really hit on
| | the dcache and icache (which are both in the NORMAL zone only, which is
| | why Andrea asked for it), and obviously your Oracle load itself seems to
| | be happily paging stuff around, which causes a lot of allocations for
| | page-ins. 
| | 
| | It only _looks_ static, because once you find the proper "balance", the
| | VM numbers themselves shouldn't change under a constant load.
| | 
| | We could make kswapd use less CPU time, of course, simply by making the
| | actual working processes do more of the work to free memory.  The total
| | work ends up being the same, though, and the advantage of kswapd is that
| | it tends to make the freeing slightly more asynchronous, which helps
| | throughput. 
| | 
| | The _disadvantage_ of kswapd is that if it goes crazy and uses up all
| | CPU time, you get bad results ;)
| | 
| | But it doesn't sound crazy in your load.  I'd be happier if the VM took
| | less CPU, of course, but for now we seem to be doing ok.
| | 
| | 		Linus
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