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Date: Thu, 22 Jun 2017 10:32:43 +0800
From: Wei Yang <richard.weiyang@...il.com>
To: Michal Hocko <mhocko@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
Andrea Arcangeli <aarcange@...hat.com>,
Jerome Glisse <jglisse@...hat.com>,
Reza Arbab <arbab@...ux.vnet.ibm.com>,
Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
qiuxishi@...wei.com, Kani Toshimitsu <toshi.kani@....com>,
slaoub@...il.com, Joonsoo Kim <js1304@...il.com>,
Andi Kleen <ak@...ux.intel.com>,
David Rientjes <rientjes@...gle.com>,
Daniel Kiper <daniel.kiper@...cle.com>,
Igor Mammedov <imammedo@...hat.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
LKML <linux-kernel@...r.kernel.org>,
Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 2/2] mm, memory_hotplug: do not assume ZONE_NORMAL is
default kernel zone
On Thu, Jun 01, 2017 at 10:37:46AM +0200, Michal Hocko wrote:
>From: Michal Hocko <mhocko@...e.com>
>
>Heiko Carstens has noticed that he can generate overlapping zones for
>ZONE_DMA and ZONE_NORMAL:
>DMA [mem 0x0000000000000000-0x000000007fffffff]
>Normal [mem 0x0000000080000000-0x000000017fffffff]
>
>$ cat /sys/devices/system/memory/block_size_bytes
>10000000
>$ cat /sys/devices/system/memory/memory5/valid_zones
>DMA
>$ echo 0 > /sys/devices/system/memory/memory5/online
>$ cat /sys/devices/system/memory/memory5/valid_zones
>Normal
>$ echo 1 > /sys/devices/system/memory/memory5/online
>Normal
>
>$ cat /proc/zoneinfo
>Node 0, zone DMA
>spanned 524288 <-----
>present 458752
>managed 455078
>start_pfn: 0 <-----
>
>Node 0, zone Normal
>spanned 720896
>present 589824
>managed 571648
>start_pfn: 327680 <-----
>
>The reason is that we assume that the default zone for kernel onlining
>is ZONE_NORMAL. This was a simplification introduced by the memory
>hotplug rework and it is easily fixable by checking the range overlap in
>the zone order and considering the first matching zone as the default
>one. If there is no such zone then assume ZONE_NORMAL as we have been
>doing so far.
>
>Fixes: "mm, memory_hotplug: do not associate hotadded memory to zones until online"
>Reported-by: Heiko Carstens <heiko.carstens@...ibm.com>
>Tested-by: Heiko Carstens <heiko.carstens@...ibm.com>
>Signed-off-by: Michal Hocko <mhocko@...e.com>
>---
> drivers/base/memory.c | 2 +-
> include/linux/memory_hotplug.h | 2 ++
> mm/memory_hotplug.c | 27 ++++++++++++++++++++++++---
> 3 files changed, 27 insertions(+), 4 deletions(-)
>
>diff --git a/drivers/base/memory.c b/drivers/base/memory.c
>index b86fda30ce62..c7c4e0325cdb 100644
>--- a/drivers/base/memory.c
>+++ b/drivers/base/memory.c
>@@ -419,7 +419,7 @@ static ssize_t show_valid_zones(struct device *dev,
>
> nid = pfn_to_nid(start_pfn);
> if (allow_online_pfn_range(nid, start_pfn, nr_pages, MMOP_ONLINE_KERNEL)) {
>- strcat(buf, NODE_DATA(nid)->node_zones[ZONE_NORMAL].name);
>+ strcat(buf, default_zone_for_pfn(nid, start_pfn, nr_pages)->name);
> append = true;
> }
>
>diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
>index 9e0249d0f5e4..ed167541e4fc 100644
>--- a/include/linux/memory_hotplug.h
>+++ b/include/linux/memory_hotplug.h
>@@ -309,4 +309,6 @@ extern struct page *sparse_decode_mem_map(unsigned long coded_mem_map,
> unsigned long pnum);
> extern bool allow_online_pfn_range(int nid, unsigned long pfn, unsigned long nr_pages,
> int online_type);
>+extern struct zone *default_zone_for_pfn(int nid, unsigned long pfn,
>+ unsigned long nr_pages);
> #endif /* __LINUX_MEMORY_HOTPLUG_H */
>diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>index b3895fd609f4..a0348de3e18c 100644
>--- a/mm/memory_hotplug.c
>+++ b/mm/memory_hotplug.c
>@@ -858,7 +858,7 @@ bool allow_online_pfn_range(int nid, unsigned long pfn, unsigned long nr_pages,
> {
> struct pglist_data *pgdat = NODE_DATA(nid);
> struct zone *movable_zone = &pgdat->node_zones[ZONE_MOVABLE];
>- struct zone *normal_zone = &pgdat->node_zones[ZONE_NORMAL];
>+ struct zone *default_zone = default_zone_for_pfn(nid, pfn, nr_pages);
>
> /*
> * TODO there shouldn't be any inherent reason to have ZONE_NORMAL
>@@ -872,7 +872,7 @@ bool allow_online_pfn_range(int nid, unsigned long pfn, unsigned long nr_pages,
> return true;
> return movable_zone->zone_start_pfn >= pfn + nr_pages;
> } else if (online_type == MMOP_ONLINE_MOVABLE) {
>- return zone_end_pfn(normal_zone) <= pfn;
>+ return zone_end_pfn(default_zone) <= pfn;
> }
>
> /* MMOP_ONLINE_KEEP will always succeed and inherits the current zone */
>@@ -938,6 +938,27 @@ void __ref move_pfn_range_to_zone(struct zone *zone,
> }
>
> /*
>+ * Returns a default kernel memory zone for the given pfn range.
>+ * If no kernel zone covers this pfn range it will automatically go
>+ * to the ZONE_NORMAL.
>+ */
>+struct zone *default_zone_for_pfn(int nid, unsigned long start_pfn,
>+ unsigned long nr_pages)
>+{
>+ struct pglist_data *pgdat = NODE_DATA(nid);
>+ int zid;
>+
>+ for (zid = 0; zid <= ZONE_NORMAL; zid++) {
>+ struct zone *zone = &pgdat->node_zones[zid];
>+
>+ if (zone_intersects(zone, start_pfn, nr_pages))
>+ return zone;
>+ }
>+
>+ return &pgdat->node_zones[ZONE_NORMAL];
>+}
Hmm... a corner case jumped into my mind which may invalidate this
calculation.
The case is:
Zone: | DMA | DMA32 | NORMAL |
v v v v
Phy mem: [ ] [ ]
^ ^ ^ ^
Node: | Node0 | | Node1 |
A B C D
The key point is
1. There is a hole between Node0 and Node1
2. The hole sits in a non-normal zone
Let's mark the boundary as A, B, C, D. Then we would have
node0->zone[dma21] = [A, B]
node1->zone[dma32] = [C, D]
If we want to hotplug a range in [B, C] on node0, it looks not that bad. While
if we want to hotplug a range in [B, C] on node1, it will introduce the
overlapped zone. Because the range [B, C] intersects none of the existing
zones on node1.
Do you think this is possible?
>+
>+/*
> * Associates the given pfn range with the given node and the zone appropriate
> * for the given online type.
> */
>@@ -945,7 +966,7 @@ static struct zone * __meminit move_pfn_range(int online_type, int nid,
> unsigned long start_pfn, unsigned long nr_pages)
> {
> struct pglist_data *pgdat = NODE_DATA(nid);
>- struct zone *zone = &pgdat->node_zones[ZONE_NORMAL];
>+ struct zone *zone = default_zone_for_pfn(nid, start_pfn, nr_pages);
>
> if (online_type == MMOP_ONLINE_KEEP) {
> struct zone *movable_zone = &pgdat->node_zones[ZONE_MOVABLE];
>--
>2.11.0
--
Wei Yang
Help you, Help me
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