Badari Pulavarty [off-list ref] wrote:

On Tue, 2005-07-26 at 11:11 -0700, Andrew Morton wrote:

quoted

Badari Pulavarty [off-list ref] wrote:

quoted

After KS & OLS discussions about memory pressure, I wanted to re-do
 iSCSI testing with "dd"s to see if we are throttling writes.  

 I created 50 10-GB ext3 filesystems on iSCSI luns. Test is simple
 50 dds (one per filesystem). System seems to throttle memory properly
 and making progress. (Machine doesn't respond very well for anything
 else, but my vmstat keeps running - 100% sys time).

It's important to monitor /proc/meminfo too - the amount of dirty/writeback
pages, etc.

btw, 100% system time is quite appalling.  Are you sure vmstat is telling
the truth?  If so, where's it all being spent?

Well, profile doesn't show any time in "default_idle". So
I believe, vmstat is telling the truth.

# cat /proc/meminfo
MemTotal:      7143628 kB
MemFree:         43252 kB
Buffers:         16736 kB
Cached:        6683348 kB
SwapCached:       5336 kB
Active:          14460 kB
Inactive:      6686928 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:      7143628 kB
LowFree:         43252 kB
SwapTotal:     1048784 kB
SwapFree:      1017920 kB
Dirty:         6225664 kB
Writeback:      447272 kB
Mapped:          10460 kB
Slab:           362136 kB
CommitLimit:   4620596 kB
Committed_AS:   168616 kB
PageTables:       2452 kB
VmallocTotal: 34359738367 kB
VmallocUsed:      9888 kB
VmallocChunk: 34359728447 kB
HugePages_Total:     0
HugePages_Free:      0
Hugepagesize:     2048 kB

That is extremely wrong.  dirty memory is *way* too high.

# echo 2 > /proc/profile; sleep 5;  readprofile -
m /usr/src/*12.3/System.map | sort -nr
1634737 total                                      0.5464
1468569 shrink_zone                              390.5769
 21203 unlock_page                              331.2969
 19497 release_pages                             46.8678
 19061 __wake_up_bit                            397.1042
 17936 page_referenced                           53.3810
 10679 lru_add_drain                            133.4875

And so page reclaim has gone crazy.

We need to work out why the dirty memory levels are so high.

Can you please reduce the number of filesystems, see if that reduces the
dirty levels?

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