Re: [PATCH 0/3] readahead drop behind and size adjustment

From: Rik van Riel
Date: Wed Jul 25 2007 - 11:29:07 EST


Nick Piggin wrote:

What *I* think is supposed to happen is that newly read in pages get
put on the inactive list, and unless they get accessed againbefore
being reclaimed, they are allowed to fall off the end of the list
without disturbing active data too much.

I think there is a missing piece here, that we used to ease the reclaim
pressure off the active list when the inactive list grows relatively
much larger than it (which could indicate a lot of use-once pages in
the system).

Andrew got rid of that logic for some reason which I don't know, but I
can't see that use-once would be terribly effective today (so your
results don't surprise me too much).

I suspect that reason is that use-once works great for
page cache pages, but anonymous pages share the same
LRUs and need a more balanced aging approach.

The result: an LRU list that works ok for both types
of pages most of the time, but falls over in some
workloads.

--
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the best in the world, and those who believe it already is. Each group
calls the other unpatriotic.
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