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Date: Tue, 5 Feb 2002 21:46:46 +0100
From: Pavel Machek <pavel@suse.cz>
To: Rik van Riel <riel@conectiva.com.br>
Cc: Jeff Garzik <garzik@havoc.gtf.org>, arjan@fenrus.demon.nl,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Radix-tree pagecache for 2.5
Message-ID: <20020205204646.GB628@elf.ucw.cz>
In-Reply-To: <20020205142154.D37@toy.ucw.cz> <Pine.LNX.4.33L.0202051644340.12225-100000@duckman.distro.conectiva>
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Hi!

> > > > > the biggest reason for this is that we *suck* at readahead for mmap....
> > > >
> > > > Is there not also fault overhead and similar issues related to mmap(2)
> > > > in general, that are not present with read(2)/write(2)?
> > >
> > > If a fault is more expensive than a system call, we're doing
> > > something wrong in the page fault path ;)
> >
> > You can read 128K at a time, but you can't fault 128K...
> 
> Why not ?
> 
> If the pages are present (read-ahead) and the page table
> is present, I see no reason why we couldn't fill in 32
> page table entries at once.

Ugh.

Okay, CPU will still have to fill its TLBs (it does not have to in
read case), but that is way easier operation. 

I did not think about this possibility, sorry.
									Pavel
-- 
(about SSSCA) "I don't say this lightly.  However, I really think that the U.S.
no longer is classifiable as a democracy, but rather as a plutocracy." --hpa
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