[PATCH 6/7] Fragmentation Avoidance V19: 006_percpu

Mel Gorman
2005-10-30T18:34:25Z

The freelists for each allocation type can slowly become corrupted due to
the per-cpu list. Consider what happens when the following happens

1. A 2^(MAX_ORDER-1) list is reserved for __GFP_EASYRCLM pages
2. An order-0 page is allocated from the newly reserved block
3. The page is freed and placed on the per-cpu list
4. alloc_page() is called with GFP_KERNEL as the gfp_mask
5. The per-cpu list is used to satisfy the allocation

Now, a kernel page is in the middle of a __GFP_EASYRCLM page. This means
that over long periods of the time, the anti-fragmentation scheme slowly
degrades to the standard allocator.

This patch divides the per-cpu lists into Kernel and User lists. RCLM_NORCLM
and RCLM_KERN use the Kernel list and RCLM_EASY uses the user list. Strictly
speaking, there should be three lists but as little effort is made to reclaim
RCLM_KERN pages, it is not worth the overhead *yet*.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
diff -rup -X /usr/src/patchset-0.5/bin//dontdiff linux-2.6.14-rc5-mm1-005_largealloc_tryharder/include/linux/mmzone.h linux-2.6.14-rc5-mm1-006_percpu/include/linux/mmzone.h
--- linux-2.6.14-rc5-mm1-005_largealloc_tryharder/include/linux/mmzone.h 2005-10-30 13:36:56.000000000 +0000
+++ linux-2.6.14-rc5-mm1-006_percpu/include/linux/mmzone.h 2005-10-30 13:38:14.000000000 +0000
@@ -60,12 +60,21 @@ struct zone_padding {
#define ZONE_PADDING(name)
#endif

+/*
+ * Indices into pcpu_list
+ * PCPU_KERNEL: For RCLM_NORCLM and RCLM_KERN allocations
+ * PCPU_EASY: For RCLM_EASY allocations
+ */
+#define PCPU_KERNEL 0
+#define PCPU_EASY 1
+#define PCPU_TYPES 2
+
struct per_cpu_pages {
- int count; /* number of pages in the list */
+ int count[PCPU_TYPES]; /* Number of pages on each list */
int low; /* low watermark, refill needed */
int high; /* high watermark, emptying needed */
int batch; /* chunk size for buddy add/remove */
- struct list_head list; /* the list of pages */
+ struct list_head list[PCPU_TYPES]; /* the lists of pages */
};

struct per_cpu_pageset {
@@ -80,6 +89,10 @@ struct per_cpu_pageset {
#endif
} ____cacheline_aligned_in_smp;

+/* Helpers for per_cpu_pages */
+#define pset_count(pset) (pset.count[PCPU_KERNEL] + pset.count[PCPU_EASY])
+#define for_each_pcputype(pindex) \
+ for (pindex = 0; pindex < PCPU_TYPES; pindex++)
#ifdef CONFIG_NUMA
#define zone_pcp(__z, __cpu) ((__z)->pageset[(__cpu)])
#else
diff -rup -X /usr/src/patchset-0.5/bin//dontdiff linux-2.6.14-rc5-mm1-005_largealloc_tryharder/mm/page_alloc.c linux-2.6.14-rc5-mm1-006_percpu/mm/page_alloc.c
--- linux-2.6.14-rc5-mm1-005_largealloc_tryharder/mm/page_alloc.c 2005-10-30 13:37:34.000000000 +0000
+++ linux-2.6.14-rc5-mm1-006_percpu/mm/page_alloc.c 2005-10-30 13:38:14.000000000 +0000
@@ -792,7 +792,7 @@ static int rmqueue_bulk(struct zone *zon
void drain_remote_pages(void)
{
struct zone *zone;
- int i;
+ int i, pindex;
unsigned long flags;

local_irq_save(flags);
@@ -808,9 +808,16 @@ void drain_remote_pages(void)
struct per_cpu_pages *pcp;

pcp = &pset->pcp[i];
- if (pcp->count)
- pcp->count -= free_pages_bulk(zone, pcp->count,
- &pcp->list, 0);
+ for_each_pcputype(pindex) {
+ if (!pcp->count[pindex])
+ continue;
+
+ /* Try remove all pages from the pcpu list */
+ pcp->count[pindex] -=
+ free_pages_bulk(zone,
+ pcp->count[pindex],
+ &pcp->list[pindex], 0);
+ }
}
}
local_irq_restore(flags);
@@ -821,7 +828,7 @@ void drain_remote_pages(void)
static void __drain_pages(unsigned int cpu)
{
struct zone *zone;
- int i;
+ int i, pindex;

for_each_zone(zone) {
struct per_cpu_pageset *pset;
@@ -831,8 +838,16 @@ static void __drain_pages(unsigned int c
struct per_cpu_pages *pcp;

pcp = &pset->pcp[i];
- pcp->count -= free_pages_bulk(zone, pcp->count,
- &pcp->list, 0);
+ for_each_pcputype(pindex) {
+ if (!pcp->count[pindex])
+ continue;
+
+ /* Try remove all pages from the pcpu list */
+ pcp->count[pindex] -=
+ free_pages_bulk(zone,
+ pcp->count[pindex],
+ &pcp->list[pindex], 0);
+ }
}
}
}
@@ -911,6 +926,7 @@ static void fastcall free_hot_cold_page(
struct zone *zone = page_zone(page);
struct per_cpu_pages *pcp;
unsigned long flags;
+ int pindex;

arch_free_page(page, 0);

@@ -920,11 +936,21 @@ static void fastcall free_hot_cold_page(
page->mapping = NULL;
free_pages_check(__FUNCTION__, page);
pcp = &zone_pcp(zone, get_cpu())->pcp[cold];
+
+ /*
+ * Strictly speaking, we should not be accessing the zone information
+ * here. In this case, it does not matter if the read is incorrect
+ */
+ if (get_pageblock_type(zone, page) == RCLM_EASY)
+ pindex = PCPU_EASY;
+ else
+ pindex = PCPU_KERNEL;
local_irq_save(flags);
- list_add(&page->lru, &pcp->list);
- pcp->count++;
- if (pcp->count >= pcp->high)
- pcp->count -= free_pages_bulk(zone, pcp->batch, &pcp->list, 0);
+ list_add(&page->lru, &pcp->list[pindex]);
+ pcp->count[pindex]++;
+ if (pcp->count[pindex] >= pcp->high)
+ pcp->count[pindex] -= free_pages_bulk(zone, pcp->batch,
+ &pcp->list[pindex], 0);
local_irq_restore(flags);
put_cpu();
}
@@ -967,17 +993,23 @@ buffered_rmqueue(struct zone *zone, int

if (order == 0) {
struct per_cpu_pages *pcp;
+ int pindex = PCPU_KERNEL;
+ if (alloctype == RCLM_EASY)
+ pindex = PCPU_EASY;

pcp = &zone_pcp(zone, get_cpu())->pcp[cold];
local_irq_save(flags);
- if (pcp->count <= pcp->low)
- pcp->count += rmqueue_bulk(zone, 0,
- pcp->batch, &pcp->list,
- alloctype);
- if (pcp->count) {
- page = list_entry(pcp->list.next, struct page, lru);
+ if (pcp->count[pindex] <= pcp->low)
+ pcp->count[pindex] += rmqueue_bulk(zone,
+ 0, pcp->batch,
+ &(pcp->list[pindex]),
+ alloctype);
+
+ if (pcp->count[pindex]) {
+ page = list_entry(pcp->list[pindex].next,
+ struct page, lru);
list_del(&page->lru);
- pcp->count--;
+ pcp->count[pindex]--;
}
local_irq_restore(flags);
put_cpu();
@@ -1678,7 +1710,7 @@ void show_free_areas(void)
pageset->pcp[temperature].low,
pageset->pcp[temperature].high,
pageset->pcp[temperature].batch,
- pageset->pcp[temperature].count);
+ pset_count(pageset->pcp[temperature]));
}
}

@@ -2135,18 +2167,22 @@ inline void setup_pageset(struct per_cpu
struct per_cpu_pages *pcp;

pcp = &p->pcp[0]; /* hot */
- pcp->count = 0;
+ pcp->count[PCPU_KERNEL] = 0;
+ pcp->count[PCPU_EASY] = 0;
pcp->low = 0;
- pcp->high = 6 * batch;
+ pcp->high = 3 * batch;
pcp->batch = max(1UL, 1 * batch);
- INIT_LIST_HEAD(&pcp->list);
+ INIT_LIST_HEAD(&pcp->list[PCPU_KERNEL]);
+ INIT_LIST_HEAD(&pcp->list[PCPU_EASY]);

pcp = &p->pcp[1]; /* cold*/
- pcp->count = 0;
+ pcp->count[PCPU_KERNEL] = 0;
+ pcp->count[PCPU_EASY] = 0;
pcp->low = 0;
- pcp->high = 2 * batch;
+ pcp->high = batch;
pcp->batch = max(1UL, batch/2);
- INIT_LIST_HEAD(&pcp->list);
+ INIT_LIST_HEAD(&pcp->list[PCPU_KERNEL]);
+ INIT_LIST_HEAD(&pcp->list[PCPU_EASY]);
}

#ifndef CONFIG_SPARSEMEM
@@ -2574,7 +2610,7 @@ static int zoneinfo_show(struct seq_file

pageset = zone_pcp(zone, i);
for (j = 0; j < ARRAY_SIZE(pageset->pcp); j++) {
- if (pageset->pcp[j].count)
+ if (pset_count(pageset->pcp[j]))
break;
}
if (j == ARRAY_SIZE(pageset->pcp))
@@ -2587,7 +2623,7 @@ static int zoneinfo_show(struct seq_file
"\n high: %i"
"\n batch: %i",
i, j,
- pageset->pcp[j].count,
+ pset_count(pageset->pcp[j]),
pageset->pcp[j].low,
pageset->pcp[j].high,
pageset->pcp[j].batch);