[PATCH v1 2/8] mm: convert PG_balloon to PG_offline

David Hildenbrand david at redhat.com
Mon Nov 19 10:16:10 UTC 2018


PG_balloon was introduced to implement page migration/compaction for pages
inflated in virtio-balloon. Nowadays, it is only a marker that a page is
part of virtio-balloon and therefore logically offline.

We also want to make use of this flag in other balloon drivers - for
inflated pages or when onlining a section but keeping some pages offline
(e.g. used right now by XEN and Hyper-V via set_online_page_callback()).

We are going to expose this flag to dump tools like makedumpfile. But
instead of exposing PG_balloon, let's generalize the concept of marking
pages as logically offline, so it can be reused for other purposes
later on.

Rename PG_balloon to PG_offline. This is an indicator that the page is
logically offline, the content stale and that it should not be touched
(e.g. a hypervisor would have to allocate backing storage in order for the
guest to dump an unused page).  We can then e.g. exclude such pages from
dumps.

We replace and reuse KPF_BALLOON (23), as this shouldn't really harm
(and for now the semantics stay the same).  In following patches, we will
make use of this bit also in other balloon drivers. While at it, document
PGTABLE.

Cc: Jonathan Corbet <corbet at lwn.net>
Cc: Alexey Dobriyan <adobriyan at gmail.com>
Cc: Mike Rapoport <rppt at linux.vnet.ibm.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Christian Hansen <chansen3 at cisco.com>
Cc: Vlastimil Babka <vbabka at suse.cz>
Cc: "Kirill A. Shutemov" <kirill.shutemov at linux.intel.com>
Cc: Stephen Rothwell <sfr at canb.auug.org.au>
Cc: Matthew Wilcox <willy at infradead.org>
Cc: "Michael S. Tsirkin" <mst at redhat.com>
Cc: Michal Hocko <mhocko at suse.com>
Cc: Pavel Tatashin <pasha.tatashin at oracle.com>
Cc: Alexander Duyck <alexander.h.duyck at linux.intel.com>
Cc: Naoya Horiguchi <n-horiguchi at ah.jp.nec.com>
Cc: Miles Chen <miles.chen at mediatek.com>
Cc: David Rientjes <rientjes at google.com>
Cc: Konstantin Khlebnikov <koct9i at gmail.com>
Cc: Kazuhito Hagio <k-hagio at ab.jp.nec.com>
Signed-off-by: David Hildenbrand <david at redhat.com>
---
 Documentation/admin-guide/mm/pagemap.rst |  9 ++++++---
 fs/proc/page.c                           |  4 ++--
 include/linux/balloon_compaction.h       |  8 ++++----
 include/linux/page-flags.h               | 11 +++++++----
 include/uapi/linux/kernel-page-flags.h   |  2 +-
 tools/vm/page-types.c                    |  2 +-
 6 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
index 3f7bade2c231..340a5aee9b80 100644
--- a/Documentation/admin-guide/mm/pagemap.rst
+++ b/Documentation/admin-guide/mm/pagemap.rst
@@ -75,9 +75,10 @@ number of times a page is mapped.
     20. NOPAGE
     21. KSM
     22. THP
-    23. BALLOON
+    23. OFFLINE
     24. ZERO_PAGE
     25. IDLE
+    26. PGTABLE
 
  * ``/proc/kpagecgroup``.  This file contains a 64-bit inode number of the
    memory cgroup each page is charged to, indexed by PFN. Only available when
@@ -118,8 +119,8 @@ Short descriptions to the page flags
     identical memory pages dynamically shared between one or more processes
 22 - THP
     contiguous pages which construct transparent hugepages
-23 - BALLOON
-    balloon compaction page
+23 - OFFLINE
+    page is logically offline
 24 - ZERO_PAGE
     zero page for pfn_zero or huge_zero page
 25 - IDLE
@@ -128,6 +129,8 @@ Short descriptions to the page flags
     Note that this flag may be stale in case the page was accessed via
     a PTE. To make sure the flag is up-to-date one has to read
     ``/sys/kernel/mm/page_idle/bitmap`` first.
+26 - PGTABLE
+    page is in use as a page table
 
 IO related page flags
 ---------------------
diff --git a/fs/proc/page.c b/fs/proc/page.c
index 6c517b11acf8..378401af4d9d 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -152,8 +152,8 @@ u64 stable_page_flags(struct page *page)
 	else if (page_count(page) == 0 && is_free_buddy_page(page))
 		u |= 1 << KPF_BUDDY;
 
-	if (PageBalloon(page))
-		u |= 1 << KPF_BALLOON;
+	if (PageOffline(page))
+		u |= 1 << KPF_OFFLINE;
 	if (PageTable(page))
 		u |= 1 << KPF_PGTABLE;
 
diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
index cbe50da5a59d..f111c780ef1d 100644
--- a/include/linux/balloon_compaction.h
+++ b/include/linux/balloon_compaction.h
@@ -95,7 +95,7 @@ extern int balloon_page_migrate(struct address_space *mapping,
 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
 				       struct page *page)
 {
-	__SetPageBalloon(page);
+	__SetPageOffline(page);
 	__SetPageMovable(page, balloon->inode->i_mapping);
 	set_page_private(page, (unsigned long)balloon);
 	list_add(&page->lru, &balloon->pages);
@@ -111,7 +111,7 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
  */
 static inline void balloon_page_delete(struct page *page)
 {
-	__ClearPageBalloon(page);
+	__ClearPageOffline(page);
 	__ClearPageMovable(page);
 	set_page_private(page, 0);
 	/*
@@ -141,13 +141,13 @@ static inline gfp_t balloon_mapping_gfp_mask(void)
 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
 				       struct page *page)
 {
-	__SetPageBalloon(page);
+	__SetPageOffline(page);
 	list_add(&page->lru, &balloon->pages);
 }
 
 static inline void balloon_page_delete(struct page *page)
 {
-	__ClearPageBalloon(page);
+	__ClearPageOffline(page);
 	list_del(&page->lru);
 }
 
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 50ce1bddaf56..f91da3d0a67e 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -670,7 +670,7 @@ PAGEFLAG_FALSE(DoubleMap)
 #define PAGE_TYPE_BASE	0xf0000000
 /* Reserve		0x0000007f to catch underflows of page_mapcount */
 #define PG_buddy	0x00000080
-#define PG_balloon	0x00000100
+#define PG_offline	0x00000100
 #define PG_kmemcg	0x00000200
 #define PG_table	0x00000400
 
@@ -700,10 +700,13 @@ static __always_inline void __ClearPage##uname(struct page *page)	\
 PAGE_TYPE_OPS(Buddy, buddy)
 
 /*
- * PageBalloon() is true for pages that are on the balloon page list
- * (see mm/balloon_compaction.c).
+ * PageOffline() indicates that the pages is logically offline although the
+ * containing section is online. (e.g. inflated in a balloon driver or
+ * not onlined when onlining the section).
+ * The content of these pages is effectively stale. Such pages should not
+ * be touched (read/write/dump/save) except by their owner.
  */
-PAGE_TYPE_OPS(Balloon, balloon)
+PAGE_TYPE_OPS(Offline, offline)
 
 /*
  * If kmemcg is enabled, the buddy allocator will set PageKmemcg() on
diff --git a/include/uapi/linux/kernel-page-flags.h b/include/uapi/linux/kernel-page-flags.h
index 21b9113c69da..6f2f2720f3ac 100644
--- a/include/uapi/linux/kernel-page-flags.h
+++ b/include/uapi/linux/kernel-page-flags.h
@@ -32,7 +32,7 @@
 
 #define KPF_KSM			21
 #define KPF_THP			22
-#define KPF_BALLOON		23
+#define KPF_OFFLINE		23
 #define KPF_ZERO_PAGE		24
 #define KPF_IDLE		25
 #define KPF_PGTABLE		26
diff --git a/tools/vm/page-types.c b/tools/vm/page-types.c
index 37908a83ddc2..6c38d3b862e4 100644
--- a/tools/vm/page-types.c
+++ b/tools/vm/page-types.c
@@ -133,7 +133,7 @@ static const char * const page_flag_names[] = {
 	[KPF_NOPAGE]		= "n:nopage",
 	[KPF_KSM]		= "x:ksm",
 	[KPF_THP]		= "t:thp",
-	[KPF_BALLOON]		= "o:balloon",
+	[KPF_OFFLINE]		= "o:offline",
 	[KPF_PGTABLE]		= "g:pgtable",
 	[KPF_ZERO_PAGE]		= "z:zero_page",
 	[KPF_IDLE]              = "i:idle_page",
-- 
2.17.2



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