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Subject[v5 6/6] mm/memory_hotplug: optimize memory hotplug
Date
During memory hotplugging we traverse struct pages three times:

1. memset(0) in sparse_add_one_section()
2. loop in __add_section() to set do: set_page_node(page, nid); and
SetPageReserved(page);
3. loop in memmap_init_zone() to call __init_single_pfn()

This patch removes the first two loops, and leaves only loop 3. All struct
pages are initialized in one place, the same as it is done during boot.

The benefits:
- We improve memory hotplug performance because we are not evicting the
cache several times and also reduce loop branching overhead.

- Remove condition from hotpath in __init_single_pfn(), that was added in
order to fix the problem that was reported by Bharata in the above email
thread, thus also improve performance during normal boot.

- Make memory hotplug more similar to the boot memory initialization path
because we zero and initialize struct pages only in one function.

- Simplifies memory hotplug struct page initialization code, and thus
enables future improvements, such as multi-threading the initialization
of struct pages in order to improve hotplug performance even further on
larger machines.

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
---
drivers/base/node.c | 2 ++
include/linux/memory.h | 1 +
mm/memory_hotplug.c | 27 ++++++++-------------------
mm/page_alloc.c | 28 ++++++++++------------------
mm/sparse.c | 8 +++++++-
5 files changed, 28 insertions(+), 38 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index d7cfc8d8a5c5..51de4af290ac 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -405,6 +405,8 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, int nid,

if (!mem_blk)
return -EFAULT;
+
+ mem_blk->nid = nid;
if (!node_online(nid))
return 0;

diff --git a/include/linux/memory.h b/include/linux/memory.h
index 9f8cd856ca1e..31ca3e28b0eb 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h
@@ -33,6 +33,7 @@ struct memory_block {
void *hw; /* optional pointer to fw/hw data */
int (*phys_callback)(struct memory_block *);
struct device dev;
+ int nid; /* NID for this memory block */
};

int arch_get_memory_phys_device(unsigned long start_pfn);
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 477e183a4ac7..6a9ba14e18ed 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -250,7 +250,6 @@ static int __meminit __add_section(int nid, unsigned long phys_start_pfn,
struct vmem_altmap *altmap, bool want_memblock)
{
int ret;
- int i;

if (pfn_valid(phys_start_pfn))
return -EEXIST;
@@ -259,23 +258,6 @@ static int __meminit __add_section(int nid, unsigned long phys_start_pfn,
if (ret < 0)
return ret;

- /*
- * Make all the pages reserved so that nobody will stumble over half
- * initialized state.
- * FIXME: We also have to associate it with a node because page_to_nid
- * relies on having page with the proper node.
- */
- for (i = 0; i < PAGES_PER_SECTION; i++) {
- unsigned long pfn = phys_start_pfn + i;
- struct page *page;
- if (!pfn_valid(pfn))
- continue;
-
- page = pfn_to_page(pfn);
- set_page_node(page, nid);
- SetPageReserved(page);
- }
-
if (!want_memblock)
return 0;

@@ -908,8 +890,15 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
int nid;
int ret;
struct memory_notify arg;
+ struct memory_block *mem;
+
+ /*
+ * We can't use pfn_to_nid() because nid might be stored in struct page
+ * which is not yet initialized. Instead, we find nid from memory block.
+ */
+ mem = find_memory_block(__pfn_to_section(pfn));
+ nid = mem->nid;

- nid = pfn_to_nid(pfn);
/* associate pfn range with the zone */
zone = move_pfn_range(online_type, nid, pfn, nr_pages);

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cb416723538f..8bf3b9c215c1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1181,10 +1181,9 @@ static void free_one_page(struct zone *zone,
}

static void __meminit __init_single_page(struct page *page, unsigned long pfn,
- unsigned long zone, int nid, bool zero)
+ unsigned long zone, int nid)
{
- if (zero)
- mm_zero_struct_page(page);
+ mm_zero_struct_page(page);
set_page_links(page, zone, nid, pfn);
init_page_count(page);
page_mapcount_reset(page);
@@ -1198,12 +1197,6 @@ static void __meminit __init_single_page(struct page *page, unsigned long pfn,
#endif
}

-static void __meminit __init_single_pfn(unsigned long pfn, unsigned long zone,
- int nid, bool zero)
-{
- return __init_single_page(pfn_to_page(pfn), pfn, zone, nid, zero);
-}
-
#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
static void __meminit init_reserved_page(unsigned long pfn)
{
@@ -1222,7 +1215,7 @@ static void __meminit init_reserved_page(unsigned long pfn)
if (pfn >= zone->zone_start_pfn && pfn < zone_end_pfn(zone))
break;
}
- __init_single_pfn(pfn, zid, nid, true);
+ __init_single_page(pfn_to_page(pfn), pfn, zid, nid);
}
#else
static inline void init_reserved_page(unsigned long pfn)
@@ -1539,7 +1532,7 @@ static unsigned long __init deferred_init_pages(int nid, int zid,
} else {
page++;
}
- __init_single_page(page, pfn, zid, nid, true);
+ __init_single_page(page, pfn, zid, nid);
nr_pages++;
}
return (nr_pages);
@@ -5332,6 +5325,7 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
pg_data_t *pgdat = NODE_DATA(nid);
unsigned long pfn;
unsigned long nr_initialised = 0;
+ struct page *page;
#ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
struct memblock_region *r = NULL, *tmp;
#endif
@@ -5393,6 +5387,11 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
#endif

not_early:
+ page = pfn_to_page(pfn);
+ __init_single_page(page, pfn, zone, nid);
+ if (context == MEMMAP_HOTPLUG)
+ SetPageReserved(page);
+
/*
* Mark the block movable so that blocks are reserved for
* movable at startup. This will force kernel allocations
@@ -5409,15 +5408,8 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
* because this is done early in sparse_add_one_section
*/
if (!(pfn & (pageblock_nr_pages - 1))) {
- struct page *page = pfn_to_page(pfn);
-
- __init_single_page(page, pfn, zone, nid,
- context != MEMMAP_HOTPLUG);
set_pageblock_migratetype(page, MIGRATE_MOVABLE);
cond_resched();
- } else {
- __init_single_pfn(pfn, zone, nid,
- context != MEMMAP_HOTPLUG);
}
}
}
diff --git a/mm/sparse.c b/mm/sparse.c
index 7af5e7a92528..775e1a4fd95e 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -816,7 +816,13 @@ int __meminit sparse_add_one_section(struct pglist_data *pgdat,
goto out;
}

- memset(memmap, 0, sizeof(struct page) * PAGES_PER_SECTION);
+#ifdef CONFIG_DEBUG_VM
+ /*
+ * Poison uninitialized struct pages in order to catch invalid flags
+ * combinations.
+ */
+ memset(memmap, PAGE_POISON_PATTERN, sizeof(struct page) * PAGES_PER_SECTION);
+#endif

section_mark_present(ms);

--
2.16.2
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