* Christoph Lameter [off-list ref] [2011-01-21 09:55:17]:

On Fri, 21 Jan 2011, Balbir Singh wrote:

quoted

* Christoph Lameter [off-list ref] [2011-01-20 09:00:09]:

quoted

On Thu, 20 Jan 2011, Balbir Singh wrote:

quoted

+	unmapped_page_control
+			[KNL] Available if CONFIG_UNMAPPED_PAGECACHE_CONTROL
+			is enabled. It controls the amount of unmapped memory
+			that is present in the system. This boot option plus
+			vm.min_unmapped_ratio (sysctl) provide granular control

min_unmapped_ratio is there to guarantee that zone reclaim does not
reclaim all unmapped pages.

What you want here is a max_unmapped_ratio.

I thought about that, the logic for reusing min_unmapped_ratio was to
keep a limit beyond which unmapped page cache shrinking should stop.

Right. That is the role of it. Its a minimum to leave. You want a maximum
size of the pagte cache.

In this case we want the maximum to be as small as the minimum, but
from a general design perspective maximum does make sense.

quoted

I think you are suggesting max_unmapped_ratio as the point at which
shrinking should begin, right?

The role of min_unmapped_ratio is to never reclaim more pagecache if we
reach that ratio even if we have to go off node for an allocation.

AFAICT What you propose is a maximum size of the page cache. If the number
of page cache pages goes beyond that then you trim the page cache in
background reclaim.

quoted

quoted

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+			reclaim_unmapped_pages(priority, zone, &sc);
+
 			if (!zone_watermark_ok_safe(zone, order,

Hmmmm. Okay that means background reclaim does it. If so then we also want
zone reclaim to be able to work in the background I think.

Anything specific you had in mind, works for me in testing, but is
there anything specific that stands out in your mind that needs to be
done?

Hmmm. So this would also work in a NUMA configuration, right. Limiting the
sizes of the page cache would avoid zone reclaim through these limit. Page
cache size would be limited by the max_unmapped_ratio.

zone_reclaim only would come into play if other allocations make the
memory on the node so tight that we would have to evict more page
cache pages in direct reclaim.
Then zone_reclaim could go down to shrink the page cache size to
min_unmapped_ratio.

I'll repost with max_unmapped_ration changes

Thanks for the review! 

-- 
	Three Cheers,
	Balbir

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