Subject: Re: Limitations of current buffer cache on 32-bit ports
To: Thor Lancelot Simon <tls@rek.tjls.com>
From: Chuck Silvers <chuq@chuq.com>
List: tech-kern
Date: 07/23/2002 21:41:21
On Wed, Jul 24, 2002 at 12:33:06AM -0400, Thor Lancelot Simon wrote:
> Okay, but if we continue to cache directories and other metadata by caching
> the filesystem blocks they came from, on modern disks we will continue to
> need on the order of 32K per.  Not ideal, no?

we'd only need to do that if the directory actually contains 32k of data.
the buffers for directory data aren't always whole blocks... if the
directory ends in a fragment, then the last buffer only need be large
enough to contain the fragment.  so for 1k frag size, if the directory
contains just 1k of data, then the buffer need only use 1k of virtual space.
we'll probably want to round to a page, but that's still a vast improvement.

-Chuck