Re: lowmem_reserve (replaces protection)

[Nick Piggin]

Andrea Arcangeli wrote:
> On Wed, Oct 27, 2004 at 12:51:11AM -0400, Rik van Riel wrote:
>
> > On Wed, 27 Oct 2004, Andrea Arcangeli wrote:
> >
> >
> > > what we'll happen is that we'll blindly free a few pages from each zone,
> > > but then we'll be allowed to allocate the highmem pages, and not the
> > > normal/dma pages. So after allocating the highmem pages we invoke kswapd
> > > again and it frees again some highmem/normal/dma pages but we keep only
> > > using the highmem ones.  So for a while we may be rolling over only the
> > > highmem lru and ignoring all freed pages from the normal/dma zones.

That's what I mean when I say it can overscan the lower zones.
You don't want to change the stop condition here though because
obviously the highmem zone still has work to do - you just want
to stop scanning the lower zones.

I don't think it is a big problem though.

I do have a patch to make it use the lower zone protection watermarks
explicitly, but it is sitting on top of other stuff which I'm going
to try to get merged first...
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