[PATCH v3 15/20] mm: CONFIG_NO_PAGE_MAPCOUNT to prepare for not maintain per-page mapcounts in large folios
From: David Hildenbrand <hidden>
Date: 2025-03-03 16:31:01
Also in:
cgroups, linux-doc, linux-fsdevel, linux-mm, lkml
Subsystem:
memory management, memory management - core, the rest · Maintainers:
Andrew Morton, David Hildenbrand, Linus Torvalds
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. Signed-off-by: David Hildenbrand <redacted> --- mm/Kconfig | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)
diff --git a/mm/Kconfig b/mm/Kconfig
index 4034a0441f650..e4bdcf11d1b86 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig@@ -881,8 +881,25 @@ 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 #
--
2.48.1