linux-kernel - Re: [SUGGESTION]: drop virtual merge accounting in I/O requests

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Date:	Sun, 13 Jul 2008 09:34:33 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
cc:	sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [SUGGESTION]: drop virtual merge accounting in I/O requests

> Mikulas Patocka <mpatocka@...hat.com> writes:
>
>> I'm getting crashes with InitIO A100u2w controller on Sparc64 (I had
>> to fix the endianity issues in the driver, but that's unrelated).
>
> x86-64 (and powerpc) solved this a long time ago by only doing
> opportunistic merging: as in don't announce to the block layer
> that you can merge, but try to merge anyways. This way SG lists
> are not necessarily filled completely, but it's still better
> than overflowing them in some rare cases.
>
> -Andi

There's option "biomerge" that enables that feature. I'm wondering, if 
there's some situation when it should be used.

Mikulas
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