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

From: Konstantin Khlebnikov
Date: Mon Nov 19 2018 - 06:56:25 EST

On Mon, Nov 19, 2018 at 1:16 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> 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.

Ok, makes sense.

Acked-by: Konstantin Khlebnikov <koct9i@xxxxxxxxx>

>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Christian Hansen <chansen3@xxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
> Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Cc: Miles Chen <miles.chen@xxxxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
> Cc: Kazuhito Hagio <k-hagio@xxxxxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
> 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",

Even 'o' keyword is better suits for Offline than for ballOon =)

> [KPF_PGTABLE] = "g:pgtable",
> [KPF_ZERO_PAGE] = "z:zero_page",
> [KPF_IDLE] = "i:idle_page",
> --
> 2.17.2
>