Date: Thu, 13 Jul 1995 23:21:21 -0700 From: Matt Dillon <dillon@blob.best.net> To: bugs@freebsd.org Subject: Another clue. (ufslk2/newbuf deadlock crash) Message-ID: <199507140621.XAA27589@blob.best.net>
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Ooops, I meant to send this to bugs@freebsd.org so everyone would see it.
This is another addendum to my ufslk2/newbuf deadlock / crashing bug report.
To recap: the machine locks up with nearly all the processes stuck in either
newbuf or ufslk2 sleeps. It is a heavily loaded pentium, 130+ users
online, 128MB of ram, NCR scsi, around 12G of disk. NFS is used heavily as
well (mainly it is as an NFS client).
The buffer code (kern/vfs_bio.c) seems to skip the EMPTY queue if it thinks
too much space is in use... but then it may wind up sleeping on
needsbuffer. Could this be why it seems to 'run out of buffers' and
then deadlock?
I wrote a little program to count the buf's on each of the queues and came
up with:
shell1:/home/dillon# /tmp/bq
none 0
lock 0
lru 229
vmio 0
age 0
empt 825
By the numbers, it seems a definite possibility. I also did a gdb -k kernel /dev/mem
and printed out 'bufspace' and 'maxbufspace':
(kgdb) print bufspace
$1 = 8702976
(kgdb) print maxbufspace
$2 = 8699904
(kgdb) print nbuf
$1 = 1054
maxbufspace > bufspace seems a perpetual condition (this is on a machine with 128MB
of ram). I do not quite understand how 'bufspace' can be so large when only
229 buffers (800K) is in use unless the clustering is somehow eating up the space
(128 buffers x maxclustersize ?? it gets a bit confused here).
It would seem that increasing nbuf will not help though, since there are plenty of
empty buffers.
I guess my question is: Am I barking up the wrong tree or can heavy usage cause the
cascade lockup using the above scenario?
-Matt
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