From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
The percpu pages calculations are a bit convoluted. Right now,
zone_batchsize() claims to be calculating the ->batch size, but
what actually happens is:
1. Calculate how large we want the entire pcp set to be (->high)
2. Scale that down by the ratio that we want high:batch to be
3. Adjust ->batch for good cache-coloring behavior
4. Re-derive ->high by scaling back up by the (2) ratio
We actually feed the cache-coloring scaling back in to the ->high
value, when it really only *should* apply to the batch value.
That was probably unintentional, and it was one of the things
that led us to mismatching the high:batch ratio that we saw in
the previous patch.
This patch reorganizes the code. It separates out the ->batch
and ->high calculations so that it's clear when we are
calculating each of them. It also ensures that we always
calculate ->high _first_, then derive ->batch from it, finally
we adjust ->batch for good cache coloring behavior.
Since we are no longer calculating the batch size by itself, it
is not simple to print it out in zone_pcp_init() during boot.
We, instead, print out the 'high' value. If anyone really misses
this, they can surely just read /proc/zoneinfo after boot.
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
---
linux.git-davehans/mm/page_alloc.c | 54 ++++++++++++++++++-------------------
1 file changed, 27 insertions(+), 27 deletions(-)
diff -puN mm/page_alloc.c~rename-zone_batchsize mm/page_alloc.c
--- linux.git/mm/page_alloc.c~rename-zone_batchsize 2013-10-15 09:57:07.597688692 -0700
+++ linux.git-davehans/mm/page_alloc.c 2013-10-15 09:57:07.602688914 -0700
@@ -4061,10 +4061,10 @@ static void __meminit zone_init_free_lis
static int pcp_high_to_batch_ratio = 4;
-static int zone_batchsize(struct zone *zone)
+static int calculate_zone_pcp_high(struct zone *zone)
{
#ifdef CONFIG_MMU
- int batch;
+ int high;
/*
* The per-cpu-pages pools are set to around 1000th of the
@@ -4072,26 +4072,13 @@ static int zone_batchsize(struct zone *z
*
* OK, so we don't know how big the cache is. So guess.
*/
- batch = zone->managed_pages / 1024;
- if (batch * PAGE_SIZE > 512 * 1024)
- batch = (512 * 1024) / PAGE_SIZE;
- batch /= pcp_high_to_batch_ratio;
- if (batch < 1)
- batch = 1;
-
- /*
- * Clamp the batch to a 2^n - 1 value. Having a power
- * of 2 value was found to be more likely to have
- * suboptimal cache aliasing properties in some cases.
- *
- * For example if 2 tasks are alternately allocating
- * batches of pages, one task can end up with a lot
- * of pages of one half of the possible page colors
- * and the other with pages of the other colors.
- */
- batch = rounddown_pow_of_two(batch + batch/2) - 1;
+ high = zone->managed_pages / 1024;
+ if (high * PAGE_SIZE > 512 * 1024)
+ high = (512 * 1024) / PAGE_SIZE;
+ if (high < 1)
+ high = 1;
- return batch;
+ return high;
#else
/* The deferral and batching of frees should be suppressed under NOMMU
@@ -4181,6 +4168,19 @@ static void pageset_setup_from_high_mark
unsigned long batch = max(1UL, high / pcp_high_to_batch_ratio);
if ((high / pcp_high_to_batch_ratio) > (PAGE_SHIFT * 8))
batch = PAGE_SHIFT * 8;
+ /*
+ * Clamp the batch to a 2^n - 1 value. Having a power
+ * of 2 value was found to be more likely to have
+ * suboptimal cache aliasing properties in some cases.
+ *
+ * For example if 2 tasks are alternately allocating
+ * batches of pages, one task can end up with a lot
+ * of pages of one half of the possible page colors
+ * and the other with pages of the other colors.
+ */
+ batch = rounddown_pow_of_two(batch + batch/2) - 1;
+ if (!batch)
+ batch = 1;
pageset_update(&p->pcp, high, batch);
}
@@ -4188,12 +4188,12 @@ static void pageset_setup_from_high_mark
static void pageset_set_high_and_batch(struct zone *zone,
struct per_cpu_pageset *pcp)
{
+ int high;
if (percpu_pagelist_fraction)
- pageset_setup_from_high_mark(pcp,
- (zone->managed_pages /
- percpu_pagelist_fraction));
+ high = (zone->managed_pages / percpu_pagelist_fraction);
else
- pageset_setup_from_batch_size(pcp, zone_batchsize(zone));
+ high = calculate_zone_pcp_high(zone);
+ pageset_setup_from_high_mark(pcp, high);
}
static void __meminit zone_pageset_init(struct zone *zone, int cpu)
@@ -4277,9 +4277,9 @@ static __meminit void zone_pcp_init(stru
zone->pageset = &boot_pageset;
if (zone->present_pages)
- printk(KERN_DEBUG " %s zone: %lu pages, LIFO batch:%u\n",
+ printk(KERN_DEBUG " %s zone: %lu pages, pcp high:%d\n",
zone->name, zone->present_pages,
- zone_batchsize(zone));
+ calculate_zone_pcp_high(zone));
}
int __meminit init_currently_empty_zone(struct zone *zone,
_
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