mm: convert PG_balloon to PG_offline

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.

[akpm@linux-foundation.org: fix comment text, per David]
Link: http://lkml.kernel.org/r/20181119101616.8901-3-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Konstantin Khlebnikov <koct9i@gmail.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Pankaj gupta <pagupta@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
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: 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>
Cc: Kazuhito Hagio <k-hagio@ab.jp.nec.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Julien Freche <jfreche@vmware.com>
Cc: Kairui Song <kasong@redhat.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Lianbo Jiang <lijiang@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Nadav Amit <namit@vmware.com>
Cc: Omar Sandoval <osandov@fb.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Xavier Deguillard <xdeguillard@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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
 ---------------------