On Thu, 2009-02-12 at 13:22 +0800, Zhang, Yanmin wrote:
> On Sat, 2009-01-24 at 09:36 +0200, Pekka Enberg wrote:
> > On Fri, 2009-01-23 at 10:22 -0500, Christoph Lameter wrote:
> > >> No there is another way. Increase the allocator order to 3 for the
> > >> kmalloc-8192 slab then multiple 8k blocks can be allocated from one of the
> > >> larger chunks of data gotten from the page allocator. That will allow slub
> > >> to do fast allocs.
> >
> > On Sat, Jan 24, 2009 at 4:55 AM, Zhang, Yanmin
> > <yanmin_zhang@xxxxxxxxxxxxxxx> wrote:
> > > After I change kmalloc-8192/order to 3, the result(pinned netperf UDP-U-4k)
> > > difference between SLUB and SLQB becomes 1% which can be considered as fluctuation.
> >
> > Great. We should fix calculate_order() to be order 3 for kmalloc-8192.
> > Are you interested in doing that?
> Pekka,
>
> Sorry for the late update.
> The default order of kmalloc-8192 on 2*4 stoakley is really an issue of calculate_order.
Oh, previous patch has a compiling warning. Pls. use below patch.
From: Zhang Yanmin <yanmin.zhang@xxxxxxxxxxxxxxx>
The default order of kmalloc-8192 on 2*4 stoakley is an issue of calculate_order.
slab_size order name
-------------------------------------------------
4096 3 sgpool-128
8192 2 kmalloc-8192
16384 3 kmalloc-16384
kmalloc-8192's default order is smaller than sgpool-128's.
On 4*4 tigerton machine, a similiar issue appears on another kmem_cache.
Function calculate_order uses 'min_objects /= 2;' to shrink. Plus size calculation/checking
in slab_order, sometimes above issue appear.
Below patch against 2.6.29-rc2 fixes it.
I checked the default orders of all kmem_cache and they don't become smaller than before. So
the patch wouldn't hurt performance.
Signed-off-by Zhang Yanmin <yanmin.zhang@xxxxxxxxxxxxxxx>
---
--- linux-2.6.29-rc2/mm/slub.c 2009-02-11 00:49:48.000000000 -0500
+++ linux-2.6.29-rc2_slubcalc_order/mm/slub.c 2009-02-12 00:47:52.000000000 -0500
@@ -1844,6 +1844,7 @@ static inline int calculate_order(int si
int order;
int min_objects;
int fraction;
+ int max_objects;
/*
* Attempt to find best configuration for a slab. This
@@ -1856,6 +1857,9 @@ static inline int calculate_order(int si
min_objects = slub_min_objects;
if (!min_objects)
min_objects = 4 * (fls(nr_cpu_ids) + 1);
+ max_objects = (PAGE_SIZE << slub_max_order)/size;
+ min_objects = min(min_objects, max_objects);
+
while (min_objects > 1) {
fraction = 16;
while (fraction >= 4) {
@@ -1865,7 +1869,7 @@ static inline int calculate_order(int si
return order;
fraction /= 2;
}
- min_objects /= 2;
+ min_objects --;
}
/*
--
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