linux-kernel - Re: potential for buffer

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Message-ID: <20061230025041.GB12306@redhat.com>
Date:	Fri, 29 Dec 2006 21:50:41 -0500
From:	Dave Jones <davej@...hat.com>
To:	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: potential for buffer_head shrinkage.

On Fri, Dec 29, 2006 at 09:45:54PM -0500, Dave Jones wrote:
 > Looking at struct buffer_head, it seems that b_state
 > uses at most 15 bits, where it's defined as a 64bit entity
 > due to it being used by bit_spin_lock and friends.
 > 
 > Given it's not uncommon for a few hundred thousand of these
 > to be present, I wonder if it's worth the effort of folding
 > b_count into the upper bits of b_state, thus shrinking
 > buffer_head by 16 bits?  This would still leave 32 bits
 > 'wasted' for further bh_state_bits expansion if necessary.

My math here based on a 64 bit compile btw in case that wasn't obvious.
32 bit wouldn't leave room for expansion.

		Dave

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