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Subject[PATCH RFC 2/6] mm: convert PG_balloon to PG_offline
Date
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.

In following patches, we will make use of this bit also in other balloon
drivers. While at it, document PGTABLE.

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christian Hansen <chansen3@cisco.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Miles Chen <miles.chen@mediatek.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
Documentation/admin-guide/mm/pagemap.rst | 6 ++++++
fs/proc/page.c | 4 ++--
include/linux/balloon_compaction.h | 8 ++++----
include/linux/page-flags.h | 11 +++++++----
include/uapi/linux/kernel-page-flags.h | 1 +
tools/vm/page-types.c | 1 +
6 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
index 3f7bade2c231..9afd6bdc424b 100644
--- a/Documentation/admin-guide/mm/pagemap.rst
+++ b/Documentation/admin-guide/mm/pagemap.rst
@@ -78,6 +78,8 @@ number of times a page is mapped.
23. BALLOON
24. ZERO_PAGE
25. IDLE
+ 26. PGTABLE
+ 27. OFFLINE

* ``/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
@@ -128,6 +130,10 @@ 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
+27 - OFFLINE
+ page is logically offline

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..6c662eb0dab8 100644
--- a/include/uapi/linux/kernel-page-flags.h
+++ b/include/uapi/linux/kernel-page-flags.h
@@ -36,5 +36,6 @@
#define KPF_ZERO_PAGE 24
#define KPF_IDLE 25
#define KPF_PGTABLE 26
+#define KPF_OFFLINE 27

#endif /* _UAPILINUX_KERNEL_PAGE_FLAGS_H */
diff --git a/tools/vm/page-types.c b/tools/vm/page-types.c
index 37908a83ddc2..b219c2eafd6a 100644
--- a/tools/vm/page-types.c
+++ b/tools/vm/page-types.c
@@ -137,6 +137,7 @@ static const char * const page_flag_names[] = {
[KPF_PGTABLE] = "g:pgtable",
[KPF_ZERO_PAGE] = "z:zero_page",
[KPF_IDLE] = "i:idle_page",
+ [KPF_OFFLINE] = "o:offline",

[KPF_RESERVED] = "r:reserved",
[KPF_MLOCKED] = "m:mlocked",
--
2.17.2
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