mm: consider zone which is not fully populated to have holes

__pageblock_pfn_to_page has two users currently, set_zone_contiguous
which checks whether the given zone contains holes and
pageblock_pfn_to_page which then carefully returns a first valid page
from the given pfn range for the given zone.  This doesn't handle zones
which are not fully populated though.  Memory pageblocks can be offlined
or might not have been onlined yet.  In such a case the zone should be
considered to have holes otherwise pfn walkers can touch and play with
offline pages.

Current callers of pageblock_pfn_to_page in compaction seem to work
properly right now because they only isolate PageBuddy
(isolate_freepages_block) or PageLRU resp.  __PageMovable
(isolate_migratepages_block) which will be always false for these pages.
It would be safer to skip these pages altogether, though.

In order to do this patch adds a new memory section state
(SECTION_IS_ONLINE) which is set in memory_present (during boot time) or
in online_pages_range during the memory hotplug.  Similarly
offline_mem_sections clears the bit and it is called when the memory
range is offlined.

pfn_to_online_page helper is then added which check the mem section and
only returns a page if it is onlined already.

Use the new helper in __pageblock_pfn_to_page and skip the whole page
block in such a case.

[mhocko@suse.com: check valid section number in pfn_to_online_page (Vlastimil),
 mark sections online after all struct pages are initialized in
 online_pages_range (Vlastimil)]
Link: http://lkml.kernel.org/r/20170518164210.GD18333@dhcp22.suse.cz
Link: http://lkml.kernel.org/r/20170515085827.16474-8-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Daniel Kiper <daniel.kiper@oracle.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Reza Arbab <arbab@linux.vnet.ibm.com>
Cc: Tobias Regnery <tobias.regnery@gmail.com>
Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Xishi Qiu <qiuxishi@huawei.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 3c8cf86201c3faefe4ce28817abe026dfb1ab508..a61aede1b3911f3102f98c7060e1c95a374c4c8e 100644 (file)
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -14,6 +14,20 @@ struct memory_block;
 struct resource;
 
 #ifdef CONFIG_MEMORY_HOTPLUG
+/*
+ * Return page for the valid pfn only if the page is online. All pfn
+ * walkers which rely on the fully initialized page->flags and others
+ * should use this rather than pfn_valid && pfn_to_page
+ */
+#define pfn_to_online_page(pfn)                                \
+({                                                     \
+       struct page *___page = NULL;                    \
+       unsigned long ___nr = pfn_to_section_nr(pfn);   \
+                                                       \
+       if (___nr < NR_MEM_SECTIONS && online_section_nr(___nr))\
+               ___page = pfn_to_page(pfn);             \
+       ___page;                                        \
+})
 
 /*
  * Types for free bootmem stored in page->lru.next. These have to be in
@@ -203,6 +217,14 @@ extern void set_zone_contiguous(struct zone *zone);
 extern void clear_zone_contiguous(struct zone *zone);
 
 #else /* ! CONFIG_MEMORY_HOTPLUG */
+#define pfn_to_online_page(pfn)                        \
+({                                             \
+       struct page *___page = NULL;            \
+       if (pfn_valid(pfn))                     \
+               ___page = pfn_to_page(pfn);     \
+       ___page;                                \
+ })
+
 /*
  * Stub functions for when hotplug is off
  */

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 976a1202bec113a47519b106ba0926787afe2d4a..2aaf7e08c5a85feb4403da19a68383be882c2c77 100644 (file)
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1144,9 +1144,10 @@ extern unsigned long usemap_size(void);
  */
 #define        SECTION_MARKED_PRESENT  (1UL<<0)
 #define SECTION_HAS_MEM_MAP    (1UL<<1)
-#define SECTION_MAP_LAST_BIT   (1UL<<2)
+#define SECTION_IS_ONLINE      (1UL<<2)
+#define SECTION_MAP_LAST_BIT   (1UL<<3)
 #define SECTION_MAP_MASK       (~(SECTION_MAP_LAST_BIT-1))
-#define SECTION_NID_SHIFT      2
+#define SECTION_NID_SHIFT      3
 
 static inline struct page *__section_mem_map_addr(struct mem_section *section)
 {
@@ -1175,6 +1176,23 @@ static inline int valid_section_nr(unsigned long nr)
        return valid_section(__nr_to_section(nr));
 }
 
+static inline int online_section(struct mem_section *section)
+{
+       return (section && (section->section_mem_map & SECTION_IS_ONLINE));
+}
+
+static inline int online_section_nr(unsigned long nr)
+{
+       return online_section(__nr_to_section(nr));
+}
+
+#ifdef CONFIG_MEMORY_HOTPLUG
+void online_mem_sections(unsigned long start_pfn, unsigned long end_pfn);
+#ifdef CONFIG_MEMORY_HOTREMOVE
+void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn);
+#endif
+#endif
+
 static inline struct mem_section *__pfn_to_section(unsigned long pfn)
 {
        return __nr_to_section(pfn_to_section_nr(pfn));
@@ -1253,10 +1271,15 @@ unsigned long __init node_memmap_size_bytes(int, unsigned long, unsigned long);
 #ifdef CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
 /*
  * pfn_valid() is meant to be able to tell if a given PFN has valid memmap
- * associated with it or not. In FLATMEM, it is expected that holes always
- * have valid memmap as long as there is valid PFNs either side of the hole.
- * In SPARSEMEM, it is assumed that a valid section has a memmap for the
- * entire section.
+ * associated with it or not. This means that a struct page exists for this
+ * pfn. The caller cannot assume the page is fully initialized in general.
+ * Hotplugable pages might not have been onlined yet. pfn_to_online_page()
+ * will ensure the struct page is fully online and initialized. Special pages
+ * (e.g. ZONE_DEVICE) are never onlined and should be treated accordingly.
+ *
+ * In FLATMEM, it is expected that holes always have valid memmap as long as
+ * there is valid PFNs either side of the hole. In SPARSEMEM, it is assumed
+ * that a valid section has a memmap for the entire section.
  *
  * However, an ARM, and maybe other embedded architectures in the future
  * free memmap backing holes to save memory on the assumption the memmap is

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index caa58338d121e95901da14e38c7fdba33e3c6c29..b2ebe9ad7f6cd2e73f90be6ac70c54cca08ef074 100644 (file)
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -929,12 +929,16 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
        unsigned long i;
        unsigned long onlined_pages = *(unsigned long *)arg;
        struct page *page;
+
        if (PageReserved(pfn_to_page(start_pfn)))
                for (i = 0; i < nr_pages; i++) {
                        page = pfn_to_page(start_pfn + i);
                        (*online_page_callback)(page);
                        onlined_pages++;
                }
+
+       online_mem_sections(start_pfn, start_pfn + nr_pages);
+
        *(unsigned long *)arg = onlined_pages;
        return 0;
 }

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 73f854344735e1bfe4e21fab0b1711dc90b9168d..387f20db217c15e039247ac539e8d5213f74e2dd 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1365,7 +1365,9 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
        if (!pfn_valid(start_pfn) || !pfn_valid(end_pfn))
                return NULL;
 
-       start_page = pfn_to_page(start_pfn);
+       start_page = pfn_to_online_page(start_pfn);
+       if (!start_page)
+               return NULL;
 
        if (page_zone(start_page) != zone)
                return NULL;
@@ -7656,6 +7658,7 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
                        break;
        if (pfn == end_pfn)
                return;
+       offline_mem_sections(pfn, end_pfn);
        zone = page_zone(pfn_to_page(pfn));
        spin_lock_irqsave(&zone->lock, flags);
        pfn = start_pfn;

diff --git a/mm/sparse.c b/mm/sparse.c
index 5032c9a619de35b6b98503c70266c19ea626c0e0..9d7fd666015ee04eddb410a55a466673ba37c8ce 100644 (file)
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -222,7 +222,8 @@ void __init memory_present(int nid, unsigned long start, unsigned long end)
 
                ms = __nr_to_section(section);
                if (!ms->section_mem_map) {
-                       ms->section_mem_map = sparse_encode_early_nid(nid);
+                       ms->section_mem_map = sparse_encode_early_nid(nid) |
+                                                       SECTION_IS_ONLINE;
                        section_mark_present(ms);
                }
        }
@@ -622,6 +623,48 @@ void __init sparse_init(void)
 }
 
 #ifdef CONFIG_MEMORY_HOTPLUG
+
+/* Mark all memory sections within the pfn range as online */
+void online_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
+{
+       unsigned long pfn;
+
+       for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
+               unsigned long section_nr = pfn_to_section_nr(start_pfn);
+               struct mem_section *ms;
+
+               /* onlining code should never touch invalid ranges */
+               if (WARN_ON(!valid_section_nr(section_nr)))
+                       continue;
+
+               ms = __nr_to_section(section_nr);
+               ms->section_mem_map |= SECTION_IS_ONLINE;
+       }
+}
+
+#ifdef CONFIG_MEMORY_HOTREMOVE
+/* Mark all memory sections within the pfn range as online */
+void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
+{
+       unsigned long pfn;
+
+       for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
+               unsigned long section_nr = pfn_to_section_nr(start_pfn);
+               struct mem_section *ms;
+
+               /*
+                * TODO this needs some double checking. Offlining code makes
+                * sure to check pfn_valid but those checks might be just bogus
+                */
+               if (WARN_ON(!valid_section_nr(section_nr)))
+                       continue;
+
+               ms = __nr_to_section(section_nr);
+               ms->section_mem_map &= ~SECTION_IS_ONLINE;
+       }
+}
+#endif
+
 #ifdef CONFIG_SPARSEMEM_VMEMMAP
 static inline struct page *kmalloc_section_memmap(unsigned long pnum, int nid)
 {