Re: [patch] VM stable again?

[Rik van Riel <riel@conectiva.com.br>]

On Mon, 15 May 2000, Ingo Molnar wrote:
> On Mon, 15 May 2000, Rik van Riel wrote:
> 
> > I've thought about this but it doesn't seem worth the extra complexity
> > to me. Just making sure that while our task is freeing pages nobody
> > else will grab those pages without having also freed some pages seems
> > to be enough to me.
> 
> actually wouldnt it be simpler to always call
> try_to_free_pages() when the zone is low on memory? This will
> keep the pressure on the system to recover from the low memory
> situation, and it reuses the low_on_memory flag. The new
> free_before_allocate flag is a 'now we are really low on memory'
> flag.

This would disturb the balancing between zones. We do not
want to have this flag per-zone since it would return us
to the "16/64MB unused" problem (and I believe you've seen
it too with highmem).

> > Furthermore, the "SMP locality" you talk about will probably be
> > completely overshadowed by the non-locality of the VM freeing code
> > anyway...
> 
> But it would be a performance optimization for sure, a
> __free_pages() + __alloc_pages() is saved - this can make a big
> difference if (a mostly clean) pagecache is shrunk.

But we shrink 'count' pages at the same time. It would only save
2 operations out of a *lot*. A much bigger win could be had if
the list operations in shrink_mmap() would be made simpler or
lower overhead...

regards,

Rik
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