On Fri, 2005-09-30 at 15:44 -0300, Marcelo wrote:

Hi Peter,

On Thu, Sep 29, 2005 at 08:08:48PM +0200, Peter Zijlstra wrote:

quoted

The flesh of the CART implementation. Again comments in the file should be
clear.

Having per-zone "B1" target accounted at fault-time instead of a global target
strikes me.

The ARC algorithm adjusts the B1 target based on the fact that being-faulted-pages
were removed from the same memory region where such pages will reside.

The per-zone "B1" target as you implement it means that the B1 target accounting
happens for the zone in which the page for the faulting data has been allocated,
_not_ on the zone from which the data has been evicted. Seems quite unfair.

So for example, if a page gets removed from the HighMem zone while in the 
B1 list, and the same data gets faulted in later on a page from the normal
zone, Normal will have its "B1" target erroneously increased.

A global inactive target scaled to the zone size would get rid of that problem.

Good, good, I'll think this though, this probably means the other
targets: 'p' and 'r' would similarly benefit.

Another issue is testing: You had some very interesting numbers before, 
how are things now?

I managed to reproduce that 10% gain on the kernel build time once more,
however it seems very unstable, I generally get only 2-3%.

quoted

Signed-off-by: Peter Zijlstra <redacted>

 mm/cart.c                  |  631 +++++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 682 insertions(+), 35 deletions(-)

Index: linux-2.6-git/mm/cart.c
===================================================================

--- /dev/null
+++ linux-2.6-git/mm/cart.c

@@ -0,0 +1,639 @@

<snip>

quoted

+#define cart_cT ((zone)->nr_active + (zone)->nr_inactive + (zone)->free_pages)
+#define cart_cB ((zone)->present_pages)
+
+#define T2B(x) (((x) * cart_cB) / cart_cT)
+#define B2T(x) (((x) * cart_cT) / cart_cB)
+
+#define size_T1 ((zone)->nr_active)
+#define size_T2 ((zone)->nr_inactive)
+
+#define list_T1 (&(zone)->active_list)
+#define list_T2 (&(zone)->inactive_list)
+
+#define cart_p ((zone)->nr_p)
+#define cart_q ((zone)->nr_q)
+
+#define size_B1 ((zone)->nr_evicted_active)
+#define size_B2 ((zone)->nr_evicted_inactive)
+
+#define nr_Ns ((zone)->nr_shortterm)
+#define nr_Nl (size_T1 + size_T2 - nr_Ns)

These defines are not not easy to read inside the code which
uses them, I personally think that "zone->nr_.." explicitly is 
much clearer.

Yes, I plan to replace them by explicit referenced, however they were
handy while playing with the definitions. And since nobody outside of
the cart code still refers to them I plan to rename the struct zone
members to match these names; zone->nr_active to zone->size_T1 and
zone->active_list to zone->list_T1.

-- 
Peter Zijlstra [off-list ref]

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>