Re: [patch for playing] 2.5.65 patch to support > 256 disks

Badari Pulavarty
2003-03-24T22:54:03Z

On Monday 24 March 2003 02:22 pm, Douglas Gilbert wrote:
> Badari Pulavarty wrote:
> > On Saturday 22 March 2003 04:05 am, Andrew Morton wrote:
> >>OK, thanks. So with 48 disks you've lost five megabytes to
> >> blkdev_requests and deadline_drq objects. With 4000 disks, you're
> >> toast. That's enough request structures to put 200 gigabytes of memory
> >> under I/O ;)
> >>
> >>We need to make the request structures dymanically allocated for other
> >>reasons (which I cannot immediately remember) but it didn't happen. I
> >>guess we have some motivation now.
> >
> > Here is the list of slab caches which consumed more than 1 MB
> > in the process of inserting 4000 disks.
> >
> > #insmod scsi_debug.ko add_host=4 num_devs=1000
> >
> > deadline_drq before:1280 after:1025420 diff:1024140 size:64
> > incr:65544960 blkdev_requests before:1280 after:1025400 diff:1024120
> > size:156 incr:159762720
> >
> > * deadline_drq, blkdev_requests consumed almost 80 MB. We need to fix
> > this.
> >
> > inode_cache before:700 after:140770 diff:140070 size:364
> > incr:50985480 dentry_cache before:4977 after:145061 diff:140084
> > size:172 incr:24094448
> >
> > * inode cache increased by 50 MB, dentry cache 24 MB.
> > It looks like we cached 140,000 inodes. I wonder why ?
> >
> > <snip/>
>
> Badari,
> What number do you get from
> # cd /sys; du -a | wc
> when you have 4000 disks?

[root@elm3b78 sysfs]# du -a | wc -l
140735

Okay. That explains the inodes.

>
> Also scsi_debug should use only 8 MB (default) for
> simulated storage shared between all pseudo disks
> (i.e. not 8 MB per simulated host).

Hmm. When I did
insmod scsi_debug.o add_host=1 num_devs=4000
it used 8MB.

But when I did
insmod scsi_debug.o add_host=4 num_devs=1000
it used 32 MB. So I assumed it is per host.

Before:
size-8192 8 8 8192 8 8 2 : 8 4 : 9
12 10 2 0 0 37 : 3 12 7 0
After:
size-8192 4010 4010 8192 4010 4010 2 : 8 4 : 4010
4014 4012 2 0 0 37 : 4006 4014 4011 0

Thanks,
Badari