On Thu, 22 Mar 2001, Stephen C. Tweedie wrote:
> Hi,
>
> There is what appears to be a simple thinko in kswapd. We really
> ought to keep kswapd running as long as there is either a free space
> or an inactive page shortfall; but right now we only keep going if
> _both_ are short.
>
> Diff below. With this change, I've got a 64MB box running Applix and
> Star Office with multiple open documents plus a few other big apps
> running, and switching desktops or going between documents is once
> more nice and snappy. Running a normal heavily populated desktop in
> 256MB used to be painful, with much apparently unnecessary swapping,
> if we had background page-cache intensive operations (eg find|wc)
> going on: the patched kernel feels much better interactively,
> presumably because kswapd is now doing the work it is supposed to do,
> instead of forcing normal apps to go into page stealing mode
> themselves.
OTOH, this change is very bad for sustained load of many tasks (make
-j30) and triggers vm oscillations. In the vmstat output below, you
can see the oscillation between push too much out to swap, and then
pull it all right back in again. It continues through the entire
build with the cost seen in the time numbers. (the ac20.virgin run
was worse by 30 secs than average, but that doesn't matter much)
I've tried this change here myself before. I think this trying to
use 'how much memory is free _now_' as a parameter is wrong because
that information is stale as soon as you get it.. or will be before
you actually get anything done with it. I know I've had good results
by throwing all of the loops out and just tell kswapd to go after a
smallish but useful size chunk whenever it's is awakened and go to
sleep again unconditionally (ala bdflush).
-Mike
2.4.2.ac20.virgin +change
real 9m2.872s 11m24.705s
user 7m23.090s 7m29.440s
sys 0m35.120s 0m41.280s
procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
17 17 1 49536 8872 1216 31348 432 800 268 200 341 1073 80 20 0
19 15 0 49284 7812 1240 31984 560 0 378 0 269 523 93 7 0
16 17 0 48440 6296 1268 32212 596 0 361 0 286 525 94 6 0
19 12 1 47728 1744 1312 32260 544 1584 349 462 512 1608 89 11 0
11 16 1 52716 12916 1256 35896 800 5644 234 1592 1136 2032 59 13 29
14 23 0 49748 18592 1308 36420 2580 0 860 0 706 1347 91 9 0
27 12 0 49236 6188 1352 37396 1132 0 370 0 364 640 89 11 0
32 10 0 50928 1688 1340 37944 1004 0 294 0 329 630 89 11 0
25 15 2 48748 1880 1052 34584 600 2088 280 787 730 2308 89 11 0
20 9 3 76344 1452 616 54908 424 9016 153 2411 1188 3534 55 36 8
18 13 3 86344 1432 284 49828 1092 16788 454 4212 2063 6043 59 24 16
18 17 2 81060 1460 308 47756 3520 3572 1313 893 957 1911 77 23 0
8 22 1 75420 22864 356 45568 4608 8416 1437 2126 1528 3958 81 8 11
4 25 0 63456 64244 460 44576 5880 0 3014 0 1439 1956 66 6 28
0 23 0 60380 64052 696 47368 3884 0 1941 0 1646 2486 11 9 80
1 35 2 59972 53580 876 49136 1520 0 591 0 856 1314 7 10 83
0 33 0 59188 49228 984 49544 808 0 283 0 424 747 11 11 78
0 30 1 59188 45168 1088 50348 608 0 227 0 333 626 12 10 78
3 27 0 58056 42312 1144 50236 628 0 219 0 273 579 13 9 78
0 32 1 58056 36640 1264 51336 620 0 262 0 310 704 21 7 72
1 29 0 58056 35068 1340 51996 536 0 184 0 251 623 18 6 76
procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
2 30 0 57300 28216 1368 51944 368 0 146 0 241 582 66 15 19
0 31 0 56896 22116 1384 52228 404 0 157 0 243 825 28 13 60
3 29 0 56080 18052 1396 52160 328 0 164 0 219 838 33 7 61
27 4 0 56080 8712 1424 52680 12 0 137 7 229 493 77 10 14
28 3 0 54040 1460 1428 50516 0 708 87 177 236 406 87 13 0
22 8 2 40644 1432 1412 32952 0 9208 94 2726 1119 2866 56 16 28
30 0 1 39372 1432 1100 30404 0 3144 0 807 302 1442 95 5 0
29 1 1 83928 1424 152 52504 160 24372 443 6095 1932 8542 60 33 8
30 0 2 84220 1432 152 44516 36 9864 23 2471 359 1444 85 15 0
29 1 1 84728 1432 160 36252 804 11140 508 2787 426 2338 90 10 0
18 21 1 106944 1448 124 26752 8548 36396 3405 9101 3750 10160 40 46 14
3 32 1 95940 36476 136 54668 40632 24104 12292 6028 5610 5505 46 34 20
5 14 0 84008 50636 136 53776 4572 0 1292 0 526 720 96 4 0
0 31 0 70928 62820 188 52940 6896 0 1931 0 1008 1342 54 6 40
0 33 1 68000 60016 236 53932 1860 0 1498 0 672 1475 7 12 80
0 27 1 68000 60392 328 55236 1148 0 367 0 489 808 3 13 84
0 35 1 68000 45964 528 56728 1056 0 622 0 606 1089 9 12 79
1 38 2 68000 34632 664 57656 428 0 350 0 411 767 14 10 76
1 32 1 67500 29384 700 58700 336 0 609 0 296 670 24 14 62
0 31 1 67500 25800 756 59348 260 0 270 0 238 629 25 14 61
0 30 1 67500 22496 804 59976 452 0 162 0 249 606 20 15 65
procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
2 30 0 66128 20152 828 59872 484 0 164 0 249 787 12 16 72
2 28 1 64372 19572 860 59388 416 0 176 0 214 829 18 13 69
0 30 1 64372 15452 872 60340 692 0 241 0 215 926 29 10 62
3 27 0 63976 10972 924 60692 388 0 173 0 222 1041 37 8 56
23 10 0 63404 1944 956 61192 276 0 265 0 260 710 75 10 15
23 10 0 55912 1460 972 51976 84 1072 138 268 387 1137 81 19 0
31 0 1 56912 1432 984 51380 0 1948 60 685 441 1947 87 13 0
30 0 0 53072 1432 980 43660 0 0 3 0 125 559 91 9 0
31 0 0 49516 1452 964 39540 0 0 6 0 109 428 86 14 0
30 0 1 52532 1460 528 42184 24 0 87 64 166 860 91 9 0
28 2 1 66340 1432 220 28508 724 27248 652 6860 1780 6486 60 37 3
25 11 1 90176 1432 120 31684 3412 21744 1159 5438 1456 7274 62 38 0
9 23 1 112836 3776 128 49752 14204 18340 4972 4588 2449 5469 50 25 25
17 19 1 112276 9660 132 61376 7156 3188 2464 797 1007 1827 93 7 0
18 9 0 106452 7676 132 63292 4732 0 1400 0 361 624 95 5 0
15 15 0 99796 15272 148 65036 6024 0 1640 0 547 786 97 3 0
17 15 0 91072 20892 176 63416 2608 0 1306 0 345 766 95 5 0
30 0 0 86872 20460 228 62344 352 0 496 0 175 381 88 12 0
6 29 0 73896 40984 292 53296 1740 0 508 0 544 953 95 5 0
6 39 1 65640 36820 568 50996 1588 0 1081 0 877 1528 89 7 4
3 30 0 62900 34872 624 50848 504 0 527 0 287 536 59 13 29
procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
2 30 0 60936 32628 668 51380 192 0 327 0 263 734 43 12 45
1 29 0 60388 27824 680 51736 404 0 145 0 236 732 45 13 42
0 30 0 56808 34432 688 50712 932 0 266 0 225 753 46 7 47
0 30 0 56808 32476 712 51232 420 0 136 0 221 801 12 13 75
1 29 1 56416 31120 724 51416 408 0 131 0 221 766 14 11 75
0 31 1 55992 27196 732 52012 444 0 144 0 240 829 23 6 70
0 32 1 55204 24556 736 52080 476 0 174 0 238 924 56 5 39
4 26 1 54920 20936 748 52552 508 0 167 0 218 889 26 16 58
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