* Re: 2.4.5-rc1 shm paging blocker
2004-03-17 15:43 ` Andrea Arcangeli
@ 2004-03-17 21:19 ` Andrea Arcangeli
0 siblings, 0 replies; 3+ messages in thread
From: Andrea Arcangeli @ 2004-03-17 21:19 UTC (permalink / raw)
To: Andrew Morton, Linus Torvalds; +Cc: linux-kernel, Martin J. Bligh
On Wed, Mar 17, 2004 at 04:43:14PM +0100, Andrea Arcangeli wrote:
> it seems the testing I did on 2.6.5-rc1 was incorrect (after testing
Ok I solved it. The testing I did was perfectly correct.
But the new changes were colliding especially with objrmap and I didn't expect
a special collision breaking _only_ objrmap (this has nothing to do with the
anon_vma work I did on top of objrmap, Martin's tree will have the same problem
that I had). The new changes alone works fine, but in combination with objrmap
they cause everything to go into taking the nap in blk_congestion_wait. Since
I tested objrmap previously extensively (on 2.6.3) I excluded originally that
it could be a problem that could trigger only in combination with objrmap, but
apparently the new code threats the referenced pages differently. This is the
fix, and I don't need this fix to avoid a system-hang-livelock with 2.6.4/2.6.3
(or with 2.6.5-rc1 with the patches backed out).
It wasn't very easy to debug since there are around 200 tasks all
rescheduling and all cpus calling shrink_cache in a live lock loop and then
going back to sleep, and it's not a deadlock, but the machine hangs forever and
clicking reboot is the only way out.
--- 2.6.5-rc1-aa1/mm/objrmap.c.~1~ 2004-03-17 18:32:58.000000000 +0100
+++ 2.6.5-rc1-aa1/mm/objrmap.c 2004-03-17 21:39:05.760714768 +0100
@@ -151,14 +151,12 @@ page_referenced_inode(struct page *page)
{
struct address_space *mapping = page->as.mapping;
struct vm_area_struct *vma;
- int referenced;
+ int referenced = 0;
BUG_ON(PageSwapCache(page));
if (down_trylock(&mapping->i_shared_sem))
- return 1;
-
- referenced = 0;
+ goto out;
list_for_each_entry(vma, &mapping->i_mmap, shared)
referenced += page_referenced_one(vma, page);
@@ -167,7 +165,7 @@ page_referenced_inode(struct page *page)
referenced += page_referenced_one(vma, page);
up(&mapping->i_shared_sem);
-
+ out:
return referenced;
}
this is 2.6.5-rc1 + objrmap:
got shmid 32768
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
11 2 0 927636 10776 44168 0 0 7 1 270 12 0 0 100 0
25 3 0 704792 10776 263604 0 0 0 0 1087 28592 10 91 0 0
32 0 0 590800 10776 373492 0 0 0 0 1084 151 15 85 0 0
46 1 0 471056 10776 489024 0 0 0 220 1132 104 14 86 0 0
53 1 0 393480 10784 562660 0 0 0 16 1087 91 15 85 0 0
60 0 0 315264 10792 636704 0 0 0 24 1086 90 15 85 0 0
67 0 0 249208 10792 698788 0 0 0 0 1084 83 15 85 0 0
74 0 0 214112 10792 729796 0 0 0 0 1084 89 18 82 0 0
81 1 0 149384 10792 790452 0 0 0 0 1085 89 15 85 0 0
81 0 0 105992 10792 829960 0 0 0 0 1085 79 17 83 0 0
88 0 0 60736 10792 871100 0 0 0 0 1085 81 15 85 0 0
89 0 0 3880 10536 924532 0 0 0 0 1091 68 15 85 0 0
91 1 0 2248 5768 928348 0 0 0 28 1092 151 8 92 0 0
89 18 588 11864 660 920564 216 640 216 640 7108 756 2 98 0 0
92 20 908 13276 532 918532 88 376 88 376 1960 317 2 98 0 0
92 21 964 13188 532 918440 112 88 112 88 959 170 3 97 0 0
90 18 652 2068 540 930364 272 132 280 132 985 175 4 96 0 0
92 14 700 2092 532 930448 68 156 68 156 1733 248 2 98 0 0
92 17 656 2016 532 930340 156 120 156 120 1110 325 4 96 0 0
90 24 12040 2532 188 937616 772 11972 920 12012 13078 1857 1 99 0 0
89 33 11992 3184 184 938300 604 380 648 428 3211 851 1 99 0 0
91 33 11964 3012 184 938328 24 36 24 36 969 127 1 99 0 0
91 39 12272 2348 164 938756 272 416 304 416 1406 373 1 99 0 0
92 36 13952 2300 152 940492 1704 2868 2716 2868 4864 923 1 99 0 0
[hang - live lock]
this is 2.6.5-rc1 + objrmap + the above fix:
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
9 1 0 934448 5400 43832 0 0 128 9 270 111 1 4 91 3
27 1 0 728920 5400 245588 0 0 0 0 1089 18437 11 89 0 0
41 4 0 592296 5400 378120 0 0 0 0 1083 100 13 87 0 0
49 1 0 516944 5400 449384 0 0 0 0 1086 89 15 85 0 0
56 1 0 449224 5408 513092 0 0 0 44 1087 91 15 85 0 0
69 0 0 372944 5416 585028 0 0 0 16 1089 110 14 86 0 0
69 0 0 302080 5416 652212 0 0 0 0 1085 68 15 85 0 0
76 0 0 276664 5416 673428 0 0 0 0 1086 83 15 85 0 0
76 1 0 204984 5416 741360 0 0 0 0 1083 70 14 86 0 0
83 0 0 162400 5416 779848 0 0 0 0 1085 81 15 86 0 0
83 0 0 111728 5420 826764 0 0 0 472 1095 88 13 87 0 0
90 1 0 64288 5420 870012 0 0 0 0 1195 86 15 85 0 0
90 1 0 24224 5420 906256 0 0 0 0 1083 73 15 86 0 0
92 4 0 2064 2500 927944 0 0 0 856 1214 143 11 89 0 0
91 35 4124 3016 1532 925900 64 2304 64 2324 1298 1092 9 91 0 0
95 25 7520 1996 1428 926948 3560 5816 3560 5820 1356 6653 10 90 0 0
80 43 25236 2704 168 937332 2144 17916 2144 17916 1371 8706 6 94 0 0
93 42 33312 3308 172 938176 1680 9752 2428 9752 1417 7547 2 99 0 0
99 71 44388 2232 176 931668 3392 11536 3720 11536 1503 21226 5 95 0 0
99 67 49540 2316 160 934400 2940 6084 2940 6084 1424 4030 0 100 0 0
97 59 53808 3408 164 931584 3196 5068 3392 5068 1426 2600 0 100 0 0
57 72 62420 5112 152 923976 3824 8200 3824 8200 1438 12514 2 98 0 0
99 87 69792 2928 152 927704 3184 9288 3184 9288 1518 11193 1 99 0 0
90 74 74392 3984 152 925828 2904 5556 2904 5556 1389 2431 0 100 0 0
70 82 81580 2748 152 921060 5672 8156 5672 8156 1398 17712 1 99 0 0
94 80 88064 2232 152 921404 5008 7900 5008 7900 1453 17488 1 100 0 0
99 73 93668 5044 172 920308 3372 6340 3532 6340 1437 4039 0 100 0 0
97 69 99784 2232 152 920132 3900 6664 3900 6664 1380 15020 0 100 0 0
70 71 105624 4308 152 919736 4300 7356 4300 7356 1464 9876 0 100 0 0
97 71 112260 8492 148 916520 3988 7500 3988 7500 1444 22537 0 100 0 0
49 90 118828 3668 148 914696 6076 7208 6076 7208 1464 27088 0 100 0 0
99 86 125552 3216 148 919176 2616 7608 2616 7608 1423 9301 0 100 0 0
98 84 131004 5204 148 917896 3192 6396 3192 6396 1444 2116 0 100 0 0
78 76 136884 2768 148 917520 4696 6844 4696 6844 1403 12965 0 100 0 0
84 73 142328 8108 148 913836 3504 6140 3536 6140 1363 8199 0 100 0 0
81 81 149696 5040 148 913204 4000 8356 4024 8356 1532 32326 0 100 0 0
99 81 155940 2876 148 916620 3144 6996 3144 6996 1543 7558 0 100 0 0
99 80 161800 5312 148 912484 4348 6912 4348 6912 1412 8694 0 100 0 0
99 75 168108 4428 148 914340 3656 7280 3656 7280 1443 12129 0 100 0 0
88 79 174432 3120 152 914548 4952 6936 5020 6936 1368 15244 0 100 0 0
2.6.3 + objrmap (w/o the above) fix is also working like the above w/o any live
lock condition.
So my testing was accurate, it was just my assumption that objrmap wouldn't
especially collide with the new 2.6.5-rc1 changes that was wrong and that
generated the confusion.
Now, if the new congestion-nap code is better or worse I don't know, probably
it's safer to return 0 from a failure in taking the lock anyways, so I will
apply the objrmap fix anyways (Martin you must pick it too if you want to use
objrmap on 2.6.5-rc1+), but at least now things makes sense again ;).
So now the last bit I've to fix is bttv + anon_vma (bttv is causing a BUG_ON to
trigger in xawtv context).
^ permalink raw reply [flat|nested] 3+ messages in thread