Commit e63ee43e authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

mm: CONFIG_NO_PAGE_MAPCOUNT to prepare for not maintain per-page mapcounts in large folios 

We're close to the finishing line: let's introduce a new
CONFIG_NO_PAGE_MAPCOUNT config option where we will incrementally remove
any dependencies on per-page mapcounts in large folios.  Once that's done,
we'll stop maintaining the per-page mapcounts with this config option
enabled.

CONFIG_NO_PAGE_MAPCOUNT will be EXPERIMENTAL for now, as we'll have to
learn about some of the real world impact of some of the implications.

As writing "!CONFIG_NO_PAGE_MAPCOUNT" is really nasty, let's introduce a
helper config option "CONFIG_PAGE_MAPCOUNT" that expresses the negation.

Link: https://lkml.kernel.org/r/20250303163014.1128035-16-david@redhat.com


Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Andy Lutomirks^H^Hski <luto@kernel.org>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: Michal Koutn <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: tejun heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 003fde44

mm/Kconfig

+17 −0
Original line number Diff line number Diff line
@@ -887,8 +887,25 @@ config READ_ONLY_THP_FOR_FS 
	  support of file THPs will be developed in the next few release

	  cycles.



config NO_PAGE_MAPCOUNT

	bool "No per-page mapcount (EXPERIMENTAL)"

	help

	  Do not maintain per-page mapcounts for pages part of larger

	  allocations, such as transparent huge pages.



	  When this config option is enabled, some interfaces that relied on

	  this information will rely on less-precise per-allocation information

	  instead: for example, using the average per-page mapcount in such

	  a large allocation instead of the per-page mapcount.



	  EXPERIMENTAL because the impact of some changes is still unclear.



endif # TRANSPARENT_HUGEPAGE



# simple helper to make the code a bit easier to read

config PAGE_MAPCOUNT

	def_bool !NO_PAGE_MAPCOUNT



#

# The architecture supports pgtable leaves that is larger than PAGE_SIZE

#