Date: Sun, 10 Apr 2005 18:41:56 -0700
From: "Randy.Dunlap" <rddunlap@osdl.org>
To: sai narasimhamurthy <sai_narasi@yahoo.com>
Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: increasing scsi_max_sg / max_segments for scsi writes/reads
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On Sat, 9 Apr 2005 19:35:52 -0700 (PDT) sai narasimhamurthy wrote:

| Hi, 
| I had posted a question on increasing the scsi
| read/write sectors  per command. I figured out some of
| the things, but many questions still exist. 
| 
| I was wondering why the maximum writes I could get
| from a single scsi write command could never exceed
| 204 
| 4096B  segments . I traced it to :  
| 
| static const int scsi_max_sg = PAGE_SIZE /
| sizeof(struct scatterlist)
| 
| in scsi_merge.c .(which amounts to 204)  
| 
| Is this the limit of the maximum blocks we can
| read/write through a single scsi command, atleast for
| the given kernel (2.4.29) ? How can I increase
| it??????
| 
| I am on a P3 Dell poweredgde 2400 . 

Did you read the comment immediately above that
calculation?

/*
 * scsi_malloc() can only dish out items of PAGE_SIZE or less, so we cannot
 * build a request that requires an sg table allocation of more than that.
 */

so scsi_malloc() would need some reworking to handle more.

OTOH, it appears that this is all removed in 2.6.10++, so moving to
2.6.recent is probably your best choice.

---
~Randy
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