Re: [PATCH] Reclaim orphaned swap pages

[Richard Jerrell <jerrell@missioncriticallinux.com>]

> > That's not really what I'm getting at.  Currently if you run a memory
> > intensive application, quit after it's pages are on an lru, and try to
> > restart, you won't be able to get the memory.  This is because pages which
> > are sitting around in the swap cache are not counted as free, and they
> > should be, because they are freeable.
> 
> No. Dirty swapcache pages which have pte's referencing them are not
> freeable.

If you quit the application, it no longer has ptes which are referencing
the page.  If, in addition, this page no longer has any ptes referencing
it, then it is wasting space.  That is why we free the page (providing
that the swap entry is not shared either).  Otherwise, you will run out of
memory because everything is stuck in the swap cache until it gets
laundered, regardless of whether anyone is still referencing the
page.  That is not a good thing, which is what the patch fixes.

Rich

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