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From: Badari Pulavarty <pbadari@us.ibm.com>
To: Andrew Morton <akpm@digeo.com>, dougg@torque.net
Subject: Re: [patch for playing] 2.5.65 patch to support > 256 disks
Date: Mon, 24 Mar 2003 13:32:56 -0800
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       Jens Axboe <axboe@suse.de>
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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 ? 

size-8192       before:8 after:4010 diff:4002 size:8192 incr:32784384

* 32 MB is for 4 hosts ram disk for scsi_debug  (4*8MB)

size-2048       before:112 after:4102 diff:3990 size:2060 incr:8219400
size-512        before:87 after:8085 diff:7998 size:524 incr:4190952
size-192        before:907 after:16910 diff:16003 size:204 incr:3264612
size-64         before:459 after:76500 diff:76041 size:76 incr:5779116
size-32         before:523 after:24528 diff:24005 size:44 incr:1056220

* 30MB for all other structures. I need to look closely on what these are..

Thanks,
Badari

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