Currently a zone's present_pages is calcuated as below, which is
inaccurate and may cause trouble to memory hotplug.
spanned_pages - absent_pages - memmap_pages - dma_reserve.
During fixing bugs caused by inaccurate zone->present_pages, we found
zone->present_pages has been abused. The field zone->present_pages may
have different meanings in different contexts:
1) pages existing in a zone.
2) pages managed by the buddy system.
For more discussions about the issue, please refer to:
http://lkml.org/lkml/2012/11/5/866
https://patchwork.kernel.org/patch/
1346751/
This patchset tries to introduce a new field named "managed_pages" to
struct zone, which counts "pages managed by the buddy system". And revert
zone->present_pages to count "physical pages existing in a zone", which
also keep in consistence with pgdat->node_present_pages.
We will set an initial value for zone->managed_pages in function
free_area_init_core() and will adjust it later if the initial value is
inaccurate.
For DMA/normal zones, the initial value is set to:
(spanned_pages - absent_pages - memmap_pages - dma_reserve)
Later zone->managed_pages will be adjusted to the accurate value when the
bootmem allocator frees all free pages to the buddy system in function
free_all_bootmem_node() and free_all_bootmem().
The bootmem allocator doesn't touch highmem pages, so highmem zones'
managed_pages is set to the accurate value "spanned_pages - absent_pages"
in function free_area_init_core() and won't be updated anymore.
This patch also adds a new field "managed_pages" to /proc/zoneinfo
and sysrq showmem.
[akpm@linux-foundation.org: small comment tweaks]
Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Cc: Wen Congyang <wency@cn.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Maciej Rutecki <maciej.rutecki@gmail.com>
Tested-by: Chris Clayton <chris2553@googlemail.com>
Cc: "Rafael J . Wysocki" <rjw@sisk.pl>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Minchan Kim <minchan@kernel.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Jianguo Wu <wujianguo@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
unsigned long zone_start_pfn;
/*
- * zone_start_pfn, spanned_pages and present_pages are all
- * protected by span_seqlock. It is a seqlock because it has
- * to be read outside of zone->lock, and it is done in the main
- * allocator path. But, it is written quite infrequently.
+ * spanned_pages is the total pages spanned by the zone, including
+ * holes, which is calculated as:
+ * spanned_pages = zone_end_pfn - zone_start_pfn;
*
- * The lock is declared along with zone->lock because it is
+ * present_pages is physical pages existing within the zone, which
+ * is calculated as:
+ * present_pages = spanned_pages - absent_pages(pags in holes);
+ *
+ * managed_pages is present pages managed by the buddy system, which
+ * is calculated as (reserved_pages includes pages allocated by the
+ * bootmem allocator):
+ * managed_pages = present_pages - reserved_pages;
+ *
+ * So present_pages may be used by memory hotplug or memory power
+ * management logic to figure out unmanaged pages by checking
+ * (present_pages - managed_pages). And managed_pages should be used
+ * by page allocator and vm scanner to calculate all kinds of watermarks
+ * and thresholds.
+ *
+ * Locking rules:
+ *
+ * zone_start_pfn and spanned_pages are protected by span_seqlock.
+ * It is a seqlock because it has to be read outside of zone->lock,
+ * and it is done in the main allocator path. But, it is written
+ * quite infrequently.
+ *
+ * The span_seq lock is declared along with zone->lock because it is
* frequently read in proximity to zone->lock. It's good to
* give them a chance of being in the same cacheline.
+ *
+ * Write access to present_pages and managed_pages at runtime should
+ * be protected by lock_memory_hotplug()/unlock_memory_hotplug().
+ * Any reader who can't tolerant drift of present_pages and
+ * managed_pages should hold memory hotplug lock to get a stable value.
*/
- unsigned long spanned_pages; /* total size, including holes */
- unsigned long present_pages; /* amount of memory (excluding holes) */
+ unsigned long spanned_pages;
+ unsigned long present_pages;
+ unsigned long managed_pages;
/*
* rarely used fields:
return count;
}
+static void reset_node_lowmem_managed_pages(pg_data_t *pgdat)
+{
+ struct zone *z;
+
+ /*
+ * In free_area_init_core(), highmem zone's managed_pages is set to
+ * present_pages, and bootmem allocator doesn't allocate from highmem
+ * zones. So there's no need to recalculate managed_pages because all
+ * highmem pages will be managed by the buddy system. Here highmem
+ * zone also includes highmem movable zone.
+ */
+ for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)
+ if (!is_highmem(z))
+ z->managed_pages = 0;
+}
+
/**
* free_all_bootmem_node - release a node's free pages to the buddy allocator
* @pgdat: node to be released
unsigned long __init free_all_bootmem_node(pg_data_t *pgdat)
{
register_page_bootmem_info_node(pgdat);
+ reset_node_lowmem_managed_pages(pgdat);
return free_all_bootmem_core(pgdat->bdata);
}
{
unsigned long total_pages = 0;
bootmem_data_t *bdata;
+ struct pglist_data *pgdat;
+
+ for_each_online_pgdat(pgdat)
+ reset_node_lowmem_managed_pages(pgdat);
list_for_each_entry(bdata, &bdata_list, list)
total_pages += free_all_bootmem_core(bdata);
void __ref put_page_bootmem(struct page *page)
{
unsigned long type;
+ static DEFINE_MUTEX(ppb_lock);
type = (unsigned long) page->lru.next;
BUG_ON(type < MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE ||
ClearPagePrivate(page);
set_page_private(page, 0);
INIT_LIST_HEAD(&page->lru);
+
+ /*
+ * Please refer to comment for __free_pages_bootmem()
+ * for why we serialize here.
+ */
+ mutex_lock(&ppb_lock);
__free_pages_bootmem(page, 0);
+ mutex_unlock(&ppb_lock);
}
}
return ret;
}
+ zone->managed_pages += onlined_pages;
zone->present_pages += onlined_pages;
zone->zone_pgdat->node_present_pages += onlined_pages;
if (onlined_pages) {
/* reset pagetype flags and makes migrate type to be MOVABLE */
undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
/* removal success */
+ zone->managed_pages -= offlined_pages;
zone->present_pages -= offlined_pages;
zone->zone_pgdat->node_present_pages -= offlined_pages;
totalram_pages -= offlined_pages;
return count;
}
+static void reset_node_lowmem_managed_pages(pg_data_t *pgdat)
+{
+ struct zone *z;
+
+ /*
+ * In free_area_init_core(), highmem zone's managed_pages is set to
+ * present_pages, and bootmem allocator doesn't allocate from highmem
+ * zones. So there's no need to recalculate managed_pages because all
+ * highmem pages will be managed by the buddy system. Here highmem
+ * zone also includes highmem movable zone.
+ */
+ for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)
+ if (!is_highmem(z))
+ z->managed_pages = 0;
+}
+
/**
* free_all_bootmem_node - release a node's free pages to the buddy allocator
* @pgdat: node to be released
unsigned long __init free_all_bootmem_node(pg_data_t *pgdat)
{
register_page_bootmem_info_node(pgdat);
+ reset_node_lowmem_managed_pages(pgdat);
/* free_low_memory_core_early(MAX_NUMNODES) will be called later */
return 0;
*/
unsigned long __init free_all_bootmem(void)
{
+ struct pglist_data *pgdat;
+
+ for_each_online_pgdat(pgdat)
+ reset_node_lowmem_managed_pages(pgdat);
+
/*
* We need to use MAX_NUMNODES instead of NODE_DATA(0)->node_id
* because in some case like Node0 doesn't have RAM installed
local_irq_restore(flags);
}
+/*
+ * Read access to zone->managed_pages is safe because it's unsigned long,
+ * but we still need to serialize writers. Currently all callers of
+ * __free_pages_bootmem() except put_page_bootmem() should only be used
+ * at boot time. So for shorter boot time, we shift the burden to
+ * put_page_bootmem() to serialize writers.
+ */
void __meminit __free_pages_bootmem(struct page *page, unsigned int order)
{
unsigned int nr_pages = 1 << order;
set_page_count(p, 0);
}
+ page_zone(page)->managed_pages += 1 << order;
set_page_refcounted(page);
__free_pages(page, order);
}
" isolated(anon):%lukB"
" isolated(file):%lukB"
" present:%lukB"
+ " managed:%lukB"
" mlocked:%lukB"
" dirty:%lukB"
" writeback:%lukB"
K(zone_page_state(zone, NR_ISOLATED_ANON)),
K(zone_page_state(zone, NR_ISOLATED_FILE)),
K(zone->present_pages),
+ K(zone->managed_pages),
K(zone_page_state(zone, NR_MLOCK)),
K(zone_page_state(zone, NR_FILE_DIRTY)),
K(zone_page_state(zone, NR_WRITEBACK)),
for (j = 0; j < MAX_NR_ZONES; j++) {
struct zone *zone = pgdat->node_zones + j;
- unsigned long size, realsize, memmap_pages;
+ unsigned long size, realsize, freesize, memmap_pages;
size = zone_spanned_pages_in_node(nid, j, zones_size);
- realsize = size - zone_absent_pages_in_node(nid, j,
+ realsize = freesize = size - zone_absent_pages_in_node(nid, j,
zholes_size);
/*
- * Adjust realsize so that it accounts for how much memory
+ * Adjust freesize so that it accounts for how much memory
* is used by this zone for memmap. This affects the watermark
* and per-cpu initialisations
*/
memmap_pages =
PAGE_ALIGN(size * sizeof(struct page)) >> PAGE_SHIFT;
- if (realsize >= memmap_pages) {
- realsize -= memmap_pages;
+ if (freesize >= memmap_pages) {
+ freesize -= memmap_pages;
if (memmap_pages)
printk(KERN_DEBUG
" %s zone: %lu pages used for memmap\n",
zone_names[j], memmap_pages);
} else
printk(KERN_WARNING
- " %s zone: %lu pages exceeds realsize %lu\n",
- zone_names[j], memmap_pages, realsize);
+ " %s zone: %lu pages exceeds freesize %lu\n",
+ zone_names[j], memmap_pages, freesize);
/* Account for reserved pages */
- if (j == 0 && realsize > dma_reserve) {
- realsize -= dma_reserve;
+ if (j == 0 && freesize > dma_reserve) {
+ freesize -= dma_reserve;
printk(KERN_DEBUG " %s zone: %lu pages reserved\n",
zone_names[0], dma_reserve);
}
if (!is_highmem_idx(j))
- nr_kernel_pages += realsize;
- nr_all_pages += realsize;
+ nr_kernel_pages += freesize;
+ nr_all_pages += freesize;
zone->spanned_pages = size;
- zone->present_pages = realsize;
+ zone->present_pages = freesize;
+ /*
+ * Set an approximate value for lowmem here, it will be adjusted
+ * when the bootmem allocator frees pages into the buddy system.
+ * And all highmem pages will be managed by the buddy system.
+ */
+ zone->managed_pages = is_highmem_idx(j) ? realsize : freesize;
#ifdef CONFIG_NUMA
zone->node = nid;
- zone->min_unmapped_pages = (realsize*sysctl_min_unmapped_ratio)
+ zone->min_unmapped_pages = (freesize*sysctl_min_unmapped_ratio)
/ 100;
- zone->min_slab_pages = (realsize * sysctl_min_slab_ratio) / 100;
+ zone->min_slab_pages = (freesize * sysctl_min_slab_ratio) / 100;
#endif
zone->name = zone_names[j];
spin_lock_init(&zone->lock);
"\n high %lu"
"\n scanned %lu"
"\n spanned %lu"
- "\n present %lu",
+ "\n present %lu"
+ "\n managed %lu",
zone_page_state(zone, NR_FREE_PAGES),
min_wmark_pages(zone),
low_wmark_pages(zone),
high_wmark_pages(zone),
zone->pages_scanned,
zone->spanned_pages,
- zone->present_pages);
+ zone->present_pages,
+ zone->managed_pages);
for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
seq_printf(m, "\n %-12s %lu", vmstat_text[i],
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