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SubjectRe: new OOM heuristic failure (was: Re: VM: qsbench)
At 07.52 31/10/01 -0800, Linus Torvalds wrote:
>
>On Wed, 31 Oct 2001, Rik van Riel wrote:
>>
>> Linus, it seems Lorenzo's test program gets killed due
>> to the new out_of_memory() heuristic ...
>
>Hmm.. The oom killer really only gets invoced if we're really down to zero
>swapspace (that's the _only_ non-rate-based heuristic in the whole thing).
>
>Lorenzo, can you do a "vmstat 1" and show the output of it during the
>interesting part of the test (ie around the kill).

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 139908 3588 68 3588 0 0 0 0 101 3 100 0
0
1 0 0 139908 3588 68 3588 0 0 0 0 101 7 100 0
0
1 0 0 139908 3588 68 3588 0 0 0 0 101 5 100 0
0
0 1 0 139336 1568 68 3588 2524 696 2524 696 192 180 57
2 41
1 0 0 140296 2996 68 3588 3776 4208 3776 4208 287 304 3
3 94
1 0 0 139968 2708 68 3588 288 0 288 0 110 21 96 0
4
1 0 0 139968 2708 68 3588 0 0 0 0 101 5 100 0
0
1 0 0 139968 2708 68 3588 0 0 0 0 101 5 100 0
0
1 0 0 139968 2708 68 3588 0 0 0 0 101 5 99 1
0
1 0 0 139968 2708 68 3588 0 0 0 0 101 3 100 0
0
1 0 0 139968 2708 68 3588 0 0 0 0 101 3 100 0
0
1 0 0 139968 2708 68 3588 0 0 0 12 104 9 100 0
0
0 1 0 144064 1620 64 3588 7256 6880 7256 6880 395 517 28
5 67
1 0 0 146168 2952 60 3584 5780 6720 5780 6720 396 401 0
8 92
0 1 0 151672 3580 64 3584 12744 10076 12748 10076 579 870 3
7 90
0 1 0 165496 1620 64 3388 14684 4108 14684 4108 629 1131 11
6 83
1 0 0 177912 1592 64 1624 4544 14196 4544 14200 377 355 5
2 93
0 1 0 182392 1548 60 1624 14648 8064 14648 8064 633 935 11
11 78
0 1 1 195320 2692 64 1624 14156 9600 14160 9600 605 943 3
8 89
1 0 0 195512 3516 64 400 5312 8376 5312 8376 378 374 2
8 90
1 0 1 195512 1664 64 400 22256 0 22256 0 797 1419 18
8 74
1 0 0 195512 1544 60 400 23520 0 23520 4 837 1540 13
7 80
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 195512 1660 60 400 23292 0 23292 0 832 1546 10
10 80
0 0 0 5384 250420 76 784 2212 24 2672 24 201 208 1
7 92
0 0 0 5384 250420 76 784 0 0 0 0 101 3 0 0
100
0 0 0 5384 250416 76 788 0 0 0 0 101 3 0 0
100
0 0 0 5384 250400 92 788 0 0 16 0 105 15 0 0
100
0 0 0 5384 250400 92 788 0 0 0 0 101 3 0 0
100
0 0 0 5384 250400 92 788 0 0 0 0 101 7 0 0
100

Until swpd is "139968" everything is fine and I have about 60M of
free swap (I have 256M RAM + 200M of swap and qsbench uses about 343M).
>From that point Linux starts swapping without any apparent reason (?)
because qsbench allocates its memory just once at the beginning.
I guess Linux starts swapping when qsbench scans sequentially the
whole array to check for errors after sorting, in the final stage.
I wonder why..

Linux-2.4.13:
1 0 0 109864 3820 64 396 0 0 0 0 101 3 100 0
0
1 0 0 109864 3816 68 396 0 0 4 0 107 23 100 0
0
1 0 0 109864 3816 68 396 0 0 0 0 101 5 98 2
0
1 0 0 109864 3816 68 396 0 0 0 0 101 3 100 0
0
1 0 0 109864 3816 68 396 0 0 0 0 101 3 100 0
0
1 0 0 109864 3816 68 396 0 0 0 0 102 5 100 0
0
0 1 0 112156 3224 64 508 2676 2048 2888 2052 235 239 68
1 31
procs memory swap io system
cpu
r b w swpd free buff cache si so bi bo in cs us sy
id
1 1 0 121372 3416 64 508 8896 9216 8896 9216 519 686 4
5 91
1 0 0 130460 3340 64 508 9420 9216 9420 9216 559 737 5
2 93
0 1 0 139932 3168 64 508 9644 9472 9644 9472 547 717 5
4 91
0 1 1 149532 3488 64 508 9356 9572 9356 9576 550 725 2
5 93
1 0 1 158308 4008 64 500 8484 8736 8492 8744 502 655 5
15 80
0 1 0 166244 3724 64 500 8204 8004 8204 8004 452 601 4
13 83
0 1 0 175716 4092 64 500 9104 9344 9104 9344 525 681 8
4 88
0 1 0 185188 4076 64 500 9356 9344 9356 9344 545 690 7
8 85
0 1 1 192100 3624 64 500 7544 7040 7544 7040 444 548 2
13 85
1 0 0 195512 3972 64 348 11260 3924 11264 3928 521 767 8
23 69
1 0 0 195512 4184 64 348 16812 0 16812 0 632 1074 14
25 61
0 1 0 195512 4164 64 364 19828 0 19856 0 722 1251 9
21 70
1 0 0 195512 3880 64 364 19740 0 19740 0 721 1240 10
16 74
1 0 0 195512 3752 64 396 20676 0 20736 0 752 1307 13
21 66
1 0 0 195512 3096 64 372 16260 4 16264 8 617 1040 11
23 66
1 0 0 195512 3344 68 372 7548 0 7560 0 346 493 51
5 44
0 0 0 5948 250640 80 800 328 0 768 0 132 64 29 4
67
0 0 0 5948 250640 80 800 0 0 0 0 101 3 0 0
100
0 0 0 5948 250640 80 800 0 0 0 0 104 10 0 0
100
0 0 0 5948 250640 80 800 0 0 0 0 119 44 0 0
100
0 0 0 5948 250640 80 800 0 0 0 0 104 11 0 0
100
0 0 0 5948 250640 80 800 0 0 0 0 130 61 0 0
100

Same behaviour.

Linux-2.4.14-pre5:
1 0 0 142648 3268 80 3784 0 0 0 0 101 5 99 1
0
1 0 0 142648 3268 80 3784 0 0 0 0 101 9 100 0
0
1 0 0 142648 3268 80 3784 0 0 0 0 101 3 100 0
0
1 0 0 142648 3268 80 3784 0 0 0 0 101 3 100 0
0
1 0 0 142648 3268 80 3784 0 0 0 0 101 3 100 0
0
1 0 0 142648 3268 80 3784 0 0 0 0 101 5 99 1
0
0 1 0 143404 3624 80 3784 5380 2108 5380 2116 298 346 61
2 37
0 1 0 148324 1632 76 3780 9452 7808 9452 7808 480 601 4
7 89
1 0 0 153572 3412 72 3780 11492 6044 11492 6044 560 737 6
4 90
1 0 0 165604 1584 72 2860 13952 7972 13952 7972 615 889 10
10 80
1 1 0 175076 1624 72 1624 5232 13536 5232 13536 390 339 4
6 90
0 1 0 181604 1540 76 1624 13360 7924 13364 7924 593 852 12
4 84
1 0 0 194276 2812 76 1624 12696 7704 12696 7704 575 804 8
6 86
1 0 0 195512 1640 76 556 7624 11412 7624 11412 449 488 4
5 91
1 0 0 195512 1572 72 496 21768 52 21768 56 784 1367 14
9 77
1 1 0 195512 1580 72 496 23196 0 23196 0 827 1460 14
10 76
procs memory swap io system
cpu
r b w swpd free buff cache si so bi bo in cs us sy
id
1 1 0 195512 1608 76 496 19208 0 19212 0 704 1220 15
8 77
1 0 0 195512 1728 76 496 15040 0 15040 4 572 946 48
6 47
1 0 0 195512 1612 72 496 21664 0 21664 0 782 1363 19
11 70
0 1 0 5144 250652 84 564 12120 0 12196 0 495 790 30
9 61
0 0 0 4984 250236 84 748 368 0 552 0 122 44 0 0
100
0 0 0 4984 250228 92 748 0 0 8 0 106 20 0 0
100
0 0 0 4984 250228 92 748 0 0 0 0 102 5 0 0
100
0 0 0 4984 250228 92 748 0 0 0 0 105 12 0 0
100
0 0 0 4984 250228 92 748 0 0 0 0 102 5 0 0
100
0 0 0 4984 250228 92 748 0 0 0 0 101 3 0 0
100
0 0 0 4984 250228 92 748 0 0 0 0 102 11 0 0
100
0 1 0 4984 250196 92 748 32 0 32 0 112 26 0 0
100

Same behaviour, but 2.4.13 uses less swap space.
Both kernels above seem to fall in OOM conditions, but they don't kill
qsbench.

>I could probably argue that the machine really _is_ out of memory at this
>point: no swap, and it obviously has to work very hard to free any pages.
>Read the "out_of_memory()" code (which is _really_ simple), with the
>realization that it only gets called when "try_to_free_pages()" fails and
>I think you'll agree.
>
>That said, it may be "try_to_free_pages()" itself that just gives up way
>too easily - it simply didn't matter before, because all callers just
>looped around and asked for more memory if it failed. So the code could
>still trigger too easily not because the oom() logic itself is all that
>bad, but simply because it makes the assumption that try_to_free_pages()
>only fails in bad situations.
>
> Linus


--
Lorenzo
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