Re: VM Requirement Document - v0.0

From: Tobias Ringstrom <tori@unhappy.mine.nu>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: <mike_phillips@urscorp.com>, <linux-kernel@vger.kernel.org>
Subject: Re: VM Requirement Document - v0.0
Date: Thu, 28 Jun 2001 16:04:34 +0200 (CEST)	[thread overview]
Message-ID: <Pine.LNX.4.33.0106281558250.1258-100000@boris.prodako.se> (raw)
In-Reply-To: <E15Fbyy-0006xF-00@the-village.bc.nu>

On Thu, 28 Jun 2001, Alan Cox wrote:

> > > That isnt really down to labelling pages, what you are talking qbout is what
> > > you get for free when page aging works right (eg 2.0.39) but don't get in
> > > 2.2 - and don't yet (although its coming) quite get right in 2.4.6pre.
> >
> > Correct, but all pages are not equal.
>
> That is the whole point of page aging done right. The use of a page dictates
> how it is aged before being discarded. So pages referenced once are aged
> rapidly, but once they get touched a couple of times then you know they arent
> streaming I/O. There are other related techniques like punishing pages that
> are touched when streaming I/O is done to pages further down the same file -
> FreeBSD does this one for example

Are you saying that classification of pages will not be useful?

Only looking at the page access patterns can certainly reveal a lot, but
tuning how to punish different pages is useful.

> > The problem with updatedb is that it pushes all applications to the swap,
> > and when you get back in the morning, everything has to be paged back from
> > swap just because the (stupid) OS is prepared for yet another updatedb
> > run.
>
> Updatedb is a bit odd in that it mostly sucks in metadata and the buffer to
> page cache balancing is a bit suspect IMHO.

In 2.4.6-pre, the buffer cache is no longer used for metata, right?

/Tobias