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

From: Mike Fedyk
Date: Fri Mar 12 2004 - 16:23:13 EST

Jamie Lokier wrote:
Nick Piggin wrote:

In Linux, all reclaim is driven by a memory shortage. Often it
is just because more memory is being requested for more file

Is reclaim the same as swapping, though? I'd expect pages to be
written to the swapfile speculatively, before they are needed for
reclaim. Is that one of those behaviours which everyone agrees is
sensible, but it's yet to be implemented in the 2.6 VM?

Nobody has mentioned the swap cache yet. If a page is in ram, and swap and not dirty, it's counted in the swap cache.

But presumably if you are running into memory pressure, you really
will need to free those free list pages, requiring the page to be
read from disk when it is used again.

The idea is that you write pages to swap _before_ the memory pressure
arrives, which makes those pages available immediately when memory
pressure does arrive, provided they are still clean. It's speculative.

I thought Linux did this already, but I don't know the current VM well.

You're saying all anon memory should become swap_cache eventually (though, it should be a background "task" so it doesn't block userspace memory requests).

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.

Though there would have to be swap recycling algo if swap size < ram.

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