Re: [PATCH] 2.6.4-rc2-mm1: vm-split-active-lists

From: Mike Fedyk
Date: Fri Mar 12 2004 - 17:38:46 EST

Jamie Lokier wrote:
Mike Fedyk wrote:

That would have other side benefits. If the anon page matches (I'm not calling it "!dirty" since that might have other semantics in the current VM) what is in swap, it can be cleaned without performing any IO. Also, suspending will have much less IO to perform before completion.

Exactly those sort of benefits.


Btw, When you say "You're saying all anon memory should become
swap_cache eventually" it's worth noting that there are benefits to
doing it the other way too: speculatively pulling in pages that are
thought likely to be good for interactive response, at the expense of
pages which have been used more recently, and must remain in RAM for a
short while while they are considered in use, but aren't ranked so
highly based on some interactivity heuristics.

IIUC, the current VM loses the aging information as soon as a page is swapped out. You might be asking for a LFU list instead of a LRU list.
Though, a reverse LFU (MFU -- most frequently used?) used only for swap might do what you want also...

I.e. fixing the "everything swapped out in the morning" problem by
having a long term slow rebalancing in favour of pages which seem to
be requested for interactive purposes, competing against the short
term balance of whichever pages have been used recently or are
predicted by short term readahead.

There was talk in Andrea's objrmap thread about using two LRU lists, but I forget what the benefits of that were.

Both replicating RAM pages to swap, and replicating swap or
file-backed pages to RAM can be speculative and down slowly, over the
long term, and when there is little other activity or I/O.

In short, that probably would require some major surgery in the VM.

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