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SubjectRE: VM-improvment with 2.4.9-ac14 + 2.4.9-ac14-aging
Date
Ok.  So you've determined that 2.4.9-ac14 is better than 2.4.4-ac10.
Probably not terribly surprising to the majority of people here.

The more interesting question is whether 2.4.9-ac14/5 is better than
2.4.10. Why not give 2.4.10 a whirl.

-Phil

-----Original Message-----
From: linux-kernel-owner@vger.kernel.org
[mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Martin
Josefsson
Sent: Tuesday, September 25, 2001 9:01 AM
To: Alan Cox
Cc: linux-kernel@vger.kernel.org; Rik van Riel
Subject: VM-improvment with 2.4.9-ac14 + 2.4.9-ac14-aging


Hi Alan.

I have a success-story which I told Rik on irc and he asked me to mail
it
to you.

I have a fileserver with 280GB diskspace and 256MB ram, it's a celeron
366. It has two software raid0 arrays. The whole machine runs reiserfs.
(before the hardwareupgrade a little while ago it ran LVM which didn't
work fine when I tried 2.4.9-ac9 so I went back to the old kernel,
2.4.4-ac10)

2.4.4-ac10 worked but it really liked to swap in and out all the time
when
the ftp-server was active (people where downloading at 3-10MB/s) and
this
made the machine _very_ sluggish. For example it swapped out about
everything that wasn't used in the last 2-5 seconds so interactive work
on
the machine (ssh) was awful. And if several downloads where taking place
at the same time it really started swapping out and then in. and then
the
server became almost unusable to anything else, and the I/O-speeds
really
went down because of the swapping. It was swapping both in and out
during
the ftp-downloads thus killing all performance of the machine.

Now I've upgraded to 2.4.9-ac14 + 2.4.9-ac14-aging from Rik. (I patched
it
woth the reiserfs-speedup too but this shouldn't affect the swapping I
think). The machine became a completely new machine, now I don't notice
that someone's downloading files at >9MB/s from it. The interactive
usage
is much better. I tried leaving an ssh session idle on the server over
night and it was still responsive when I woke up, with 2.4.4-ac10 it
would
have taken 1-2 seconds for it to come alive again.

The machine has swapped out things like unused pages of the httpd's and
mysqld's and stuff so it has 40-50MB swap used according to top and
friends. If I run vmstat during downloads I don't see this constant swap
out/swap in behaviour anymore and the machine is much more responsive.

I do however see that it allocates new swap sometimes but not swapping
anything out. and I do see that it swaps stuff in from time to time, I
guess this ends up in the SwapCache and is later beeing discarded and
then
sometime later swapped in again and the procedure repeats.

This newly allocated swapspace that's never used seems to decrease
slowly
over time. The fact that it's allocating new swapspace doesn't really
bother me but I don't like the reason why it does it. The pages the
ftpserver uses for the I/O are only used once and then discarded. I
don't
think we should allocate new swapspace for this kind of sequential I/O.

Here's the output of 'vmstat 5' during a download from the ftpserver:

procs memory swap io system
cpu
r b w swpd free buff cache si so bi bo in cs us
sy id
0 0 0 49400 4584 15024 181276 0 0 0 0 128 74 0
0 100
0 0 0 49400 4584 15024 181276 0 0 0 0 123 74 0
0 100
0 0 0 49400 4584 15024 181276 0 0 0 0 121 74 0
0 100
0 0 1 49400 4584 15024 181276 0 0 0 2 171 73 0
0 100
0 0 0 49400 3056 15268 182608 0 0 1956 38 1088 367 1
8 91
1 0 1 49400 3056 13964 185372 0 0 7096 30 3616 894 3
30 67
2 0 1 50204 3056 13952 185512 0 0 7198 30 3675 889 4
32 64
1 0 0 50668 3056 13696 185736 11 0 6271 32 3205 797 3
29 67
2 0 1 50968 3056 13520 183756 126 0 7814 101 3826 971 13
31 57
1 0 1 51340 3056 13548 184572 3 0 7274 61 3690 912 8
32 59
1 0 0 51340 3056 13600 184556 0 0 6391 35 3298 852 4
27 69
1 0 1 51624 3056 13580 184592 0 0 8005 34 4102 1048 4
38 58
1 0 0 51668 3056 13500 184732 0 0 6607 33 3361 847 3
29 68
1 0 0 51716 3056 13460 185352 0 0 7903 37 3997 988 3
35 62
1 0 1 51716 3056 13492 185340 0 0 6890 38 3504 898 3
30 66
1 0 0 51716 3056 13172 185684 0 0 7787 34 3962 1021 2
32 65
2 0 1 51724 3056 13096 185692 0 0 6764 30 3454 969 2
28 70
2 0 1 51724 3056 13088 185696 0 0 6669 34 3316 540 70
30 0
1 0 0 51724 3056 13120 185776 0 27 7224 61 3689 904 6
32 62
1 0 0 51724 3056 13168 185868 0 0 6917 34 3521 898 2
30 68
3 0 0 51724 3060 13064 184884 0 0 7917 37 3948 935 7
36 58
0 0 0 51724 3124 13016 185436 101 0 6600 56 3276 861 7
28 66
1 0 0 51724 3056 13044 185472 0 0 6571 33 3354 880 2
30 68
1 0 0 51744 3056 12908 185616 0 0 7876 32 3992 1025 2
34 63
1 0 0 51744 3056 12944 185580 0 0 6902 30 3514 887 1
29 70
0 0 0 51744 3056 12916 185628 0 0 3610 38 1908 558 2
17 81
0 0 0 51744 3848 12956 184792 0 0 140 5 217 190 3
4 94
0 0 0 51744 4176 13020 184820 0 0 1 26 141 89 1
0 99
0 0 0 51744 4176 13020 184820 0 0 0 0 119 69 0
0 100
1 0 0 51744 4096 13020 184824 0 0 1 0 128 80 0
0 100
0 0 0 51744 4152 13020 184844 0 0 3 7 134 90 1
0 99
0 0 0 51744 4156 13020 184844 0 0 0 6 122 76 0
0 100
0 0 0 51744 4644 13020 184352 0 0 14 21 129 85 7
1 92
0 0 0 51744 4648 13020 184352 0 0 0 14 128 78 0
0 100
0 0 0 51744 4644 13020 184352 0 0 0 0 124 76 1
0 99
0 0 0 51744 4648 13020 184352 0 0 0 0 130 72 0
0 100
0 0 0 51744 4644 13020 184352 0 0 0 0 128 78 1
0 99
0 0 0 51744 4648 13020 184352 0 0 0 0 126 77 0
0 99
0 0 0 51744 4644 13020 184352 0 0 0 0 126 79 0
0 100
0 0 0 51744 4588 13020 184356 10 0 15 11 138 88 0
1 99
0 0 0 51736 3616 13040 185064 40 0 191 6 152 96 0
1 99
0 0 0 51736 3596 13060 185064 0 0 0 7 130 76 0
0 100
0 0 0 51736 3596 13060 185064 0 0 0 0 128 78 0
1 99

here you can see the increase in the swapspaceallocation. It rarely
swaps
anything out, it just allocates new swapspace. these statistics where
taken about 30 minutes ago, I just checked the amount of swap
used/allocated now (30 min later) and it's 52036 now.
I can't see any new processes started so I assume it's preallocated
swapspace.

I didn't look in /proc/meminfo when I ran that vmstat but here it is 30
minutes later:

total: used: free: shared: buffers: cached:
Mem: 261926912 258797568 3129344 32768 14131200 218222592
Swap: 127987712 53284864 74702848
MemTotal: 255788 kB
MemFree: 3056 kB
MemShared: 32 kB
Buffers: 13800 kB
Cached: 185172 kB
SwapCached: 27936 kB
Active: 142740 kB
Inact_dirty: 53728 kB
Inact_clean: 30472 kB
Inact_target: 65520 kB
HighTotal: 0 kB
HighFree: 0 kB
LowTotal: 255788 kB
LowFree: 3056 kB
SwapTotal: 124988 kB
SwapFree: 72952 kB


/Martin

Never argue with an idiot. They drag you down to their level, then beat
you with experience.

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