Hi, KOSAKI 

On 09/28/2012 06:03 AM, KOSAKI Motohiro wrote:

(9/27/12 2:47 AM), Lai Jiangshan wrote:

quoted

Currently memory_hotplug only manages the node_states[N_HIGH_MEMORY],
it forgets to manage node_states[N_NORMAL_MEMORY]. it causes
node_states[N_NORMAL_MEMORY] becomes stale.

What's mean 'stale'? I guess

: Currently memory_hotplug doesn't turn on/off node_states[N_NORMAL_MEMORY]

Right.

and
: then it will be invalid if the platform has highmem. Luckily, almost memory 
: hotplug aware platform don't have highmem, but are not all.

right?

Some platforms(32 bit) support logic-memory-hotplug.
Some platforms have movable memory.
They are all considered.

I supporse this patch only meaningful on ARM platform practically.

any platform whic supports memory-hotplug.

quoted

We add check_nodemasks_changes_online() and check_nodemasks_changes_offline()
to detect whether node_states[N_HIGH_MEMORY] and node_states[N_NORMAL_MEMORY]
are changed while hotpluging.

quoted

Also add @status_change_nid_normal to struct memory_notify, thus
the memory hotplug callbacks know whether the node_states[N_NORMAL_MEMORY]
are changed.

status_change_nid_normal is very ugly to me. When status_change_nid and 
status_change_nid_normal has positive value, they are always the same.
nid and flags value are more natual to me.

If we use flags, the semantic of "status_change_nid" is changed and we need to
change more current code, and we will add complicated to the memory hotplug
callbacks.

like this:

-		node = arg->status_change_nid;
+		if (arg->status_change_flags & (1UL << N_HIGH_MEMORY))
+			node = arg->status_change_nid;
+		else
+			node = -1;

quoted

Signed-off-by: Lai Jiangshan <redacted>
---
 Documentation/memory-hotplug.txt |    5 ++-
 include/linux/memory.h           |    1 +
 mm/memory_hotplug.c              |   94 +++++++++++++++++++++++++++++++------
 3 files changed, 83 insertions(+), 17 deletions(-)

diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt
index 6d0c251..6e6cbc7 100644
--- a/Documentation/memory-hotplug.txt
+++ b/Documentation/memory-hotplug.txt

@@ -377,15 +377,18 @@ The third argument is passed by pointer of struct memory_notify.
 struct memory_notify {
        unsigned long start_pfn;
        unsigned long nr_pages;
+       int status_change_nid_normal;
        int status_change_nid;
 }
 
 start_pfn is start_pfn of online/offline memory.
 nr_pages is # of pages of online/offline memory.
+status_change_nid_normal is set node id when N_NORMAL_MEMORY of nodemask
+is (will be) set/clear, if this is -1, then nodemask status is not changed.
 status_change_nid is set node id when N_HIGH_MEMORY of nodemask is (will be)
 set/clear. It means a new(memoryless) node gets new memory by online and a
 node loses all memory. If this is -1, then nodemask status is not changed.
-If status_changed_nid >= 0, callback should create/discard structures for the
+If status_changed_nid* >= 0, callback should create/discard structures for the
 node if necessary.
 
 --------------

diff --git a/include/linux/memory.h b/include/linux/memory.h
index ff9a9f8..a09216d 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h

@@ -53,6 +53,7 @@ int arch_get_memory_phys_device(unsigned long start_pfn);
 struct memory_notify {
 	unsigned long start_pfn;
 	unsigned long nr_pages;
+	int status_change_nid_normal;
 	int status_change_nid;
 };
 

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 6a5b90d..b62d429b 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c

@@ -460,6 +460,34 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
 	return 0;
 }
 
+static void check_nodemasks_changes_online(unsigned long nr_pages,
+	struct zone *zone, struct memory_notify *arg)
+{
+	int nid = zone_to_nid(zone);
+	enum zone_type zone_last = ZONE_NORMAL;
+
+	if (N_HIGH_MEMORY == N_NORMAL_MEMORY)
+		zone_last = ZONE_MOVABLE;

This is very strange (or ugly) code. ZONE_MOVABLE don't depend on high mem.

If we don't have HIGHMEM,
any node of N_NORMAL_MEMORY has 0...ZONE_MOVABLE

if we have HIGHMEM,
any node of N_NORMAL_MEMORY has 0...ZONE_NORMAL

quoted

+
+	if (zone_idx(zone) <= zone_last && !node_state(nid, N_NORMAL_MEMORY))
+		arg->status_change_nid_normal = nid;
+	else
+		arg->status_change_nid_normal = -1;

Wrong. The onlined node may only have high mem zone. IOW, think fake numa case etc.

"zone_idx(zone) <= zone_last" checks this case. the result is "else" branch.

quoted

+
+	if (!node_state(nid, N_HIGH_MEMORY))
+		arg->status_change_nid = nid;
+	else
+		arg->status_change_nid = -1;
+}
+
+static void set_nodemasks(int node, struct memory_notify *arg)

Too ugly. just remove this and use node_set_state() directly.

quoted

+{
+	if (arg->status_change_nid_normal >= 0)
+		node_set_state(node, N_NORMAL_MEMORY);
+
+	node_set_state(node, N_HIGH_MEMORY);
+}
+
 
 int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
 {

@@ -471,13 +499,18 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
 	struct memory_notify arg;
 
 	lock_memory_hotplug();
+	/*
+	 * This doesn't need a lock to do pfn_to_page().
+	 * The section can't be removed here because of the
+	 * memory_block->state_mutex.
+	 */

Please explain the intention of this comment. We think lock_memory_hotplug() close
a race against memory offline directly.

I move old code up. the context does not changed.

quoted

+	zone = page_zone(pfn_to_page(pfn));
+
 	arg.start_pfn = pfn;
 	arg.nr_pages = nr_pages;
-	arg.status_change_nid = -1;
+	check_nodemasks_changes_online(nr_pages, zone, &arg);
 
 	nid = page_to_nid(pfn_to_page(pfn));
-	if (node_present_pages(nid) == 0)
-		arg.status_change_nid = nid;
 
 	ret = memory_notify(MEM_GOING_ONLINE, &arg);
 	ret = notifier_to_errno(ret);

@@ -487,12 +520,6 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
 		return ret;
 	}
 	/*
-	 * This doesn't need a lock to do pfn_to_page().
-	 * The section can't be removed here because of the
-	 * memory_block->state_mutex.
-	 */
-	zone = page_zone(pfn_to_page(pfn));
-	/*
 	 * If this zone is not populated, then it is not in zonelist.
 	 * This means the page allocator ignores this zone.
 	 * So, zonelist must be updated after online.

@@ -517,7 +544,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
 	zone->present_pages += onlined_pages;
 	zone->zone_pgdat->node_present_pages += onlined_pages;
 	if (onlined_pages) {
-		node_set_state(zone_to_nid(zone), N_HIGH_MEMORY);
+		set_nodemasks(zone_to_nid(zone), &arg);
 		if (need_zonelists_rebuild)
 			build_all_zonelists(NULL, zone);
 		else

@@ -870,6 +897,44 @@ check_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
 	return offlined;
 }
 
+static void check_nodemasks_changes_offline(unsigned long nr_pages,
+		struct zone *zone, struct memory_notify *arg)
+{

This should remove ugly memory_notify argument and should be fold 
check_nodemasks_changes_online().

quoted

+	struct pglist_data *pgdat = zone->zone_pgdat;
+	unsigned long present_pages = 0;
+	enum zone_type zt, zone_last = ZONE_NORMAL;
+
+	if (N_HIGH_MEMORY == N_NORMAL_MEMORY)
+		zone_last = ZONE_MOVABLE;
+
+	for (zt = 0; zt <= zone_last; zt++)
+		present_pages += pgdat->node_zones[zt].present_pages;
+	if (zone_idx(zone) <= zone_last && nr_pages >= present_pages)
+		arg->status_change_nid_normal = zone_to_nid(zone);
+	else
+		arg->status_change_nid_normal = -1;

Wrong. Think, a zone has both normal and highmem zone and when admin 
only remove highmem area. you should check pfn too.

I checked the pfn via "zone_idx(zone) <= zone_last".

"""zone = page_zone(pfn_to_page(pfn))"""

quoted

+
+	zone_last = ZONE_MOVABLE;
+	for (; zt <= zone_last; zt++)
+		present_pages += pgdat->node_zones[zt].present_pages;
+	if (nr_pages >= present_pages)
+		arg->status_change_nid = zone_to_nid(zone);
+	else
+		arg->status_change_nid = -1;
+}
+
+static void clear_nodemasks(int node, struct memory_notify *arg)
+{
+	if (arg->status_change_nid_normal >= 0)
+		node_clear_state(node, N_NORMAL_MEMORY);
+
+	if (N_HIGH_MEMORY == N_NORMAL_MEMORY)
+		return;

You should use #ifdef. otherwise we face unreachable statement warning.

fixed.

quoted

+
+	if (arg->status_change_nid >= 0)
+		node_clear_state(node, N_HIGH_MEMORY);
+}
+
 static int __ref offline_pages(unsigned long start_pfn,
 		  unsigned long end_pfn, unsigned long timeout)
 {

@@ -903,9 +968,7 @@ static int __ref offline_pages(unsigned long start_pfn,
 
 	arg.start_pfn = start_pfn;
 	arg.nr_pages = nr_pages;
-	arg.status_change_nid = -1;
-	if (nr_pages >= node_present_pages(node))
-		arg.status_change_nid = node;
+	check_nodemasks_changes_offline(nr_pages, zone, &arg);
 
 	ret = memory_notify(MEM_GOING_OFFLINE, &arg);
 	ret = notifier_to_errno(ret);

@@ -973,10 +1036,9 @@ repeat:
 	if (!populated_zone(zone))
 		zone_pcp_reset(zone);
 
-	if (!node_present_pages(node)) {
-		node_clear_state(node, N_HIGH_MEMORY);
+	clear_nodemasks(node, &arg);
+	if (arg.status_change_nid >= 0)
 		kswapd_stop(node);
-	}
 
 	vm_total_pages = nr_free_pagecache_pages();
 	writeback_set_ratelimit();

Thank you very much for the review.
And sorry for so late respond.

Thank,
Lai

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>