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

[Rik van Riel]

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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