Re: [PATCH] 2.2.17pre7 VM enhancement Re: I/O performance on 2.4.0-test2

[jalvo@mbay.net (John Alvord)]

On Tue, 11 Jul 2000 21:32:30 +0200 (CEST), Andrea Arcangeli
<andrea@suse.de> wrote:

>On 11 Jul 2000, Juan J. Quintela wrote:
>
>>If you are copying in the background a cp and you don't touch your
>>vi/emacs/whatever pages in 2 hours (i.e. age = 0) then I think that it
>>is ok for that pages to be swaped out.  Notice that the cage pages
>>will have _initial age_  and the pages of the binaries will have an
>>_older_ age.
>
>If we want to do that we can do that. My design doesn't forbid this. I
>only avoid the overhead of the inactive list.
>
>Also note that what I was really complaining is to threat the lru_cached
>and lru_mapped list equally. If you threat them equally you get in
>troubles as I pointed out. I just want to say that lru_mapped have much
>more priority than lru_cache. If you give the higher priority with a aging
>factor, or I give higher priority with a different falling back behaviour
>it doesn't matter (with the difference that I avoid overhead of refiling
>between lru lists and I avoid to roll ex-mapped-pages in the lru_cache
>list just to decrease their age).

One question that puzzles me... cache for disk files and cache for
program data will have very unlike characteristics. Executable program
storage is typically more constant. Often disk files are read once and
throw away and program data is often reused. This isn't always true,
but it is very common.

My puzzle is how the MM system should balance between those three uses
of cache. Under pressure. it is very easy for disk file cache to
overwhelm program data and executable storage. And equally program
data can overwhelm disk file cache storage.

If there is more than enough memory, no problem. When there is not
enough, what algorithm is used to achieve an effective balance of
usage?

Thanks,

John Alvord
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