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

Douglas Gilbert
2003-03-24T22:22:51Z

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?

With two disks the count on my system is 528.

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).

Doug Gilbert