From: Dave Jones <davej@redhat.com>
To: Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: potential for buffer_head shrinkage.
Date: Fri, 29 Dec 2006 21:50:41 -0500 [thread overview]
Message-ID: <20061230025041.GB12306@redhat.com> (raw)
In-Reply-To: <20061230024554.GA12306@redhat.com>
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
--
http://www.codemonkey.org.uk
prev parent reply other threads:[~2006-12-30 2:50 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-12-30 2:45 potential for buffer_head shrinkage Dave Jones
2006-12-30 2:50 ` Dave Jones [this message]
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