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SubjectRe: 2.4.19rc2aa1 VM too aggressive?
On Tue, Jul 23, 2002 at 01:22:35PM -0700, Stephen Hemminger wrote:
> When running sequential write performance tests on 2.4.19rc3ac3 I see a
> similar problem. What happens is the page cache gets really big, then
> the machine starts swapping and becomes unusable.
>
> It seems like there needs to be some upper bound on the page cache or
> flow control on file writes to not allow the cpu to get ahead of the
> disk.

that's the write throttling.

>
> This is vmstat output when running iozone, and it does first .5 G file
> then a 1G file. The machine has lots of memory but when it fills, it
> goes off the deep end...
>
> procs memory swap io system cpu
> r b w swpd free buff cache si so bi bo in cs us sy id
> 1 0 1 0 234456 12128 542360 0 0 0 32475 1044 29 0 11 89
> 1 0 1 0 233744 12160 542360 0 0 0 62712 1065 79 0 18 82
> 0 1 0 0 303008 12160 542360 0 0 0 21751 1042 21 0 3 97
> 1 0 1 0 510140 12384 201112 0 0 0 11070 1042 18 0 14 86
> 0 1 0 0 302280 12660 542360 0 0 0 77826 1034 54 0 18 82
> 0 1 0 0 302280 12660 542360 0 0 0 0 1040 8 0 1 99
> 1 0 1 0 176144 12660 542360 0 0 0 39073 1043 23 0 12 88
> 0 1 0 0 302272 12660 542360 0 0 0 81925 1050 60 0 20 80
> 0 1 0 0 302268 12660 542360 0 0 0 0 1044 6 0 0 100
> 1 0 1 0 480496 12852 176408 0 0 0 10661 1043 18 0 14 86
> 0 1 0 0 301456 13156 542360 0 0 0 81511 1035 37 0 19 81
> 0 1 0 0 301452 13156 542360 0 0 0 0 1040 7 0 0 100
> 1 0 1 0 181724 13156 542360 0 0 0 30479 1047 18 0 10 90
> 0 1 0 0 301408 11864 543684 0 0 1 87331 1077 61 0 23 77
> 0 1 0 0 301400 11872 543684 0 0 0 2 1043 8 0 0 100
> 0 0 1 0 529624 11880 313604 0 0 0 26639 1043 1843 0 9 91
> 0 0 2 0 137892 11880 700356 0 0 0 92110 1036 2424 0 10 90
> 0 0 1 0 54688 11888 780868 0 0 0 29978 1038 515 0 2 98
> 0 1 1 7900 7024 976 848600 747 1926 1277 22411 1242 730 0 8 92
> 0 1 1 7900 7036 596 849352 1412 305 2351 738 1421 447 0 4 96
> 0 2 1 7900 7040 596 849488 1453 162 3077 174 1799 821 0 14 86
> 0 2 1 7900 7032 596 849772 888 150 1634 168 4111 1165 0 39 61

some seldom swapout is ok, the strange thing are those small
swapins/swapouts. I also assume it's writing using write(2), not with
map_shared+msync.

can you try:

echo 1000 >/proc/sys/vm/vm_mapped_ratio

I also wonder if you've quite some amount of mapped address space durign
the benchmark. In such case there's no trivial way around it, the vm
will constantly found tons of mapped address space, and it will trigger
some swapouts, however the swapins shouldn't happen so fast in such
case.

In any case the sysctl will allow you to tune for your workload.

Andrea
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