Re: 1352 NUL bytes at the end of a page? (was Re: Assertion `s && s->tree' failed: The saga continues.)

Steven Cole
2004-05-16T05:55:00Z

On Saturday 15 May 2004 10:52 pm, Linus Torvalds wrote:
>
> On Sat, 15 May 2004, Steven Cole wrote:
> >
> > OK, will do. I ran the bk exerciser script for over an hour with 2.6.6-current
> > and no CONFIG_PREEMPT and no errors. The script only reported one
> > iteration finished, while I got it to do 36 iterations over several hours earlier
> > today (with a 2.6.3-4mdk vendor kernel)
>
> Hmm.. Th ecurrent BK tree contains much of the anonvma stuff, so this
> might actually be a serious VM performance regression. That could
> effectively be hiding whatever problem you saw.

[steven@spc steven]$ vmstat -n 1 15
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
0 2 16644 3056 5288 71752 13 25 652 357 3024 357 36 35 6 22
0 1 16644 2832 5288 72036 0 0 1052 0 3155 300 20 29 0 51
1 0 16644 2708 5284 72072 0 0 788 0 2586 333 19 26 0 55
0 2 16644 3216 5288 71976 0 0 932 0 2850 291 20 26 0 54
1 1 16644 2832 5292 72500 0 0 1036 0 3093 329 20 30 0 50
0 1 16644 3088 5264 72688 0 0 1000 303 3561 449 21 35 0 43
0 2 16644 3216 5276 72384 0 0 720 0 2475 335 19 23 0 58
1 1 16644 2848 5292 72440 60 0 763 0 2544 372 18 25 0 58
0 3 16644 3152 5172 72136 0 0 776 4 2530 392 20 24 0 55
0 1 16644 3216 5200 71848 0 0 945 0 2893 375 20 27 0 53
1 1 16644 2512 5464 71488 0 0 924 260 2899 364 18 26 0 56
1 1 16644 2832 5500 71348 0 0 880 224 3714 320 20 36 0 45
1 1 16644 3208 5380 71316 0 0 932 7 2879 412 20 28 0 52
0 1 16644 3280 5356 71172 0 0 924 0 2828 348 22 27 0 51
1 0 16644 3748 5368 71728 0 0 1056 0 2867 343 17 30 0 53
[steven@spc steven]$ free
total used free shared buffers cached
Mem: 386472 384032 2440 0 3936 113748
-/+ buffers/cache: 266348 120124
Swap: 1067928 16644 1051284

>
> Andrea: have you tested under low memory and high fs load? Steven has 384M
> or RAM, which _will_ cause a lot of VM activity when doing a full kernel
> BK clone + undo + pull, which is what his test script ends up doing...
>
> It would be good to test going back to the kernel that saw the "immediate
> problem", and try that version without CONFIG_PREEMPT.
>
> Linus
>
>
I'll give that a try tomorrow. I'll let this thing (sans PREEMPT and REGPARM) cook
on Andy's script overnight. The kernel is up to date through Changeset 1.1724.

The original problem happened only about 20% of the time during bk pulls.
Prior to 4/15/04 (or perhaps a day or two before at most), it never happened.
The 'it' being the 'Assertion `s && s->tree' failed' during a bk pull.

Steven