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From: "Serge A. Babkin" <babkin@hq.icb.chel.su>
Message-Id: <199602050350.IAA24118@hq.icb.chel.su>
Subject: Re: FAT filesystem performance
To: terry@lambert.org (Terry Lambert)
Date: Mon, 5 Feb 1996 08:50:19 +0500 (GMT+0500)
Cc: luigi@labinfo.iet.unipi.it, hackers@FreeBSD.org
In-Reply-To: <199602042148.OAA06143@phaeton.artisoft.com> from "Terry Lambert" at Feb 4, 96 02:48:27 pm
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> > We use FAT filesystems both in the kernel, and in mtools.
> > For the latter, I thought there was a quick fix to the problem of
> > caching the FAT: just mmap the device, and the kernel will do caching
> > for you. Well, it does not look that simple, as the vast majority of
> > raw devices does not support mmap.
> > 
> > I am wondering: how hard would it be to add mmap() to, say, wd.c ?
> > Would it have other useful applications ?
> 
> This would be useful for mtools, but not for the kernel version of FAT.
> 
> The FAT-caching in the MACH implementation (you *could* just port the
> MACH code...) takes a significant amount of memory, IMO.

Hmm... FAT can contain at most 64K of entries, each 2 bytes long, so
the needed amount of memory (if you cache raw FAT and don't try to make
any ``cooked'' version) must be at most 128Kbytes long. IMHO the raw FAT 
is enough convenient ant takes not very much of memory.

-SB