"indefinite" wait buffer patch

[Arno J. Klaassen]

Hello,


while slowly testing releng_7, I remembered I have since about
two years the attached diff in my releng_6 sources (patch
recreated against releng_7 with low timeouts for debugging) :

it addresses the situation when one creates a huge swap-space on 
a (relatively) slow disk-subsystem : e.g. for scientific computing
it sometimes makes sense to have, e.g. 8G swap for 2G main memory
if you know you're treating N less then 2G matrices and process
is CPU-bound for quite a while for 1 matrix before switching to 
the other.
But then, when switching from one matrix to another, dmesg gets
flooded by :

  "indefinite wait buffer" 

messages.

The attached patch shows in fact that the wait buffer is never
"indefinite" (unless a real HW-problem probably) and linearly
increases timeout to match with reality.

The last chunk is just to prevent for a panic at reboot when
there is so much data swapped out that is doesn't get treated
before 'reboot-finish-time-out'.

With this patch, dmesg lookes like following (with low timeout 
values, on production systems I use 

  TIMO_CHUNK 20
  TIMO_START 1O
) :

Nov  1 20:09:52 install kernel: swap_pager: wait buffer timeout 1 (1 secs): bufobj: 0, blkno: 1649, size: 28672
Nov  1 20:09:52 install kernel: swap_pager: wait buffer timeout 2 (2 secs): bufobj: 0, blkno: 1649, size: 28672
Nov  1 20:09:52 install kernel: swap_pager: wait buffer completed (2 retry): bufobj: 0, blkno: 1649, size: 28672
Nov  1 20:37:09 install kernel: swap_pager: wait buffer timeout 1 (4 secs): bufobj: 0, blkno: 329073, size: 32768
Nov  1 20:37:10 install kernel: swap_pager: wait buffer completed (1 retry): bufobj: 0, blkno: 329073, size: 32768
Nov  1 20:39:06 install kernel: swap_pager: wait buffer timeout 1 (4 secs): bufobj: 0, blkno: 381137, size: 32768
Nov  1 20:39:07 install kernel: swap_pager: wait buffer completed (1 retry): bufobj: 0, blkno: 381137, size: 32768
Nov  1 20:39:11 install kernel: swap_pager: wait buffer timeout 1 (4 secs): bufobj: 0, blkno: 381161, size: 32768
Nov  1 20:39:14 install kernel: swap_pager: wait buffer completed (1 retry): bufobj: 0, blkno: 381161, size: 32768
Nov  1 20:39:19 install kernel: swap_pager: wait buffer timeout 1 (4 secs): bufobj: 0, blkno: 381209, size: 32768
Nov  1 20:39:20 install kernel: swap_pager: wait buffer completed (1 retry): bufobj: 0, blkno: 381209, size: 32768
Nov  1 20:43:18 install kernel: swap_pager: wait buffer timeout 1 (4 secs): bufobj: 0, blkno: 300329, size: 32768
Nov  1 20:43:18 install kernel: swap_pager: wait buffer completed (1 retry): bufobj: 0, blkno: 300329, size: 32768
Nov  1 20:44:23 install kernel: swap_pager: wait buffer timeout 1 (4 secs): bufobj: 0, blkno: 330617, size: 32768
Nov  1 20:44:24 install kernel: swap_pager: wait buffer completed (1 retry): bufobj: 0, blkno: 330617, size: 32768
Nov  1 20:44:28 install kernel: swap_pager: wait buffer timeout 1 (4 secs): bufobj: 0, blkno: 330649, size: 32768
Nov  1 20:44:28 install kernel: swap_pager: wait buffer completed (1 retry): bufobj: 0, blkno: 330649, size: 32768
Nov  1 20:44:33 install kernel: swap_pager: wait buffer timeout 1 (4 secs): bufobj: 0, blkno: 330665, size: 32768
Nov  1 20:44:36 install kernel: swap_pager: wait buffer completed (1 retry): bufobj: 0, blkno: 330665, size: 32768
Nov  1 20:45:18 install kernel: swap_pager: wait buffer timeout 1 (4 secs): bufobj: 0, blkno: 356481, size: 32768
Nov  1 20:45:18 install kernel: swap_pager: wait buffer completed (1 retry): bufobj: 0, blkno: 356481, size: 32768
Nov  1 20:45:23 install kernel: swap_pager: wait buffer timeout 1 (4 secs): bufobj: 0, blkno: 356521, size: 32768
Nov  1 20:45:27 install kernel: swap_pager: wait buffer timeout 2 (4 secs): bufobj: 0, blkno: 356521, size: 32768
Nov  1 20:45:31 install kernel: swap_pager: wait buffer completed (2 retry): bufobj: 0, blkno: 356521, size: 32768
Nov  1 20:46:37 install kernel: swap_pager: wait buffer timeout 1 (4 secs): bufobj: 0, blkno: 391113, size: 32768
Nov  1 20:46:37 install kernel: swap_pager: wait buffer completed (1 retry): bufobj: 0, blkno: 391113, size: 32768
Nov  1 20:46:42 install kernel: swap_pager: wait buffer timeout 1 (4 secs): bufobj: 0, blkno: 391129, size: 32768
Nov  1 20:46:45 install kernel: swap_pager: wait buffer completed (1 retry): bufobj: 0, blkno: 391129, size: 32768
Nov  1 20:48:18 install kernel: swap_pager: wait buffer timeout 1 (4 secs): bufobj: 0, blkno: 432249, size: 32768
Nov  1 20:48:18 install kernel: swap_pager: wait buffer completed (1 retry): bufobj: 0, blkno: 432249, size: 32768
Nov  1 20:48:25 install kernel: swap_pager: wait buffer timeout 1 (4 secs): bufobj: 0, blkno: 432273, size: 32768
Nov  1 20:48:25 install kernel: swap_pager: wait buffer completed (1 retry): bufobj: 0, blkno: 432273, size: 32768


(And then the timeout of 8 secs apperently is enough for this test setup).

Any thoughts?

Regards,

Arno


-------------- next part --------------
A non-text attachment was scrubbed...
Name: swap.patch
Type: text/x-patch
Size: 2406 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/freebsd-hackers/attachments/20071101/ea9ad9be/swap.bin
-------------- next part --------------

-- 

  Arno J. Klaassen

  SCITO S.A.
  8 rue des Haies
  F-75020 Paris, France
  http://scito.com