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Re: Working on the ddf

From: Neal H. Walfield
Subject: Re: Working on the ddf
Date: Thu, 15 Apr 2004 10:12:10 -0400
User-agent: Wanderlust/2.8.1 (Something) SEMI/1.14.3 (Ushinoya) FLIM/1.14.3 (Unebigoryƍmae) APEL/10.6 Emacs/21.2 (i386-debian-linux-gnu) MULE/5.0 (SAKAKI)

> However, if you want low-level I/O caches
> (gianluca thinks they are essential, but neal and me believe caching
> is better done at higher levels, like the filesystem), then it makes
> sense to treat cache memory specially (using extra pages).  So, some
> considerations apply here, but in general, don't worry too much about
> it.

This wasn't quite clear to me but what I think marcus is referring to
with low-level I/O caches are block level caches (i.e. versus file
system level caches).

A block level cache is going to be, at best, fairly stupid (it can
detect some types of access patterns but does not have the benefit of
knowing how files are laid out, etc. like the file system does).  As
there will rarely be more than one user of a block level device (for
obvious cache consistency reasons, e.g. one should never fsck a
mounted file system), it seems that there is little to be gained by
adding this extra level of less intelligent caching: it will only
compete for physical memory with the file system cache.


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