[PATCH] Documentation: update pagemap with SOFT_DIRTY & UFFD_WP shmem issue
STALE1868d
REVIEWED: 4 (0M)
From: Tiberiu A Georgescu <hidden>
Date: 2021-08-12 15:59:12
Also in:
linux-mm
Subsystem:
documentation, memory management - misc, the rest · Maintainers:
Jonathan Corbet, Andrew Morton, David Hildenbrand, Linus Torvalds
4 review trailers.
Mentioning the current missing functionality of the pagemap, in case someone stumbles upon unexpected behaviour. Signed-off-by: Tiberiu A Georgescu <redacted> Reviewed-by: Ivan Teterevkov <redacted> Reviewed-by: Florian Schmidt <redacted> Reviewed-by: Carl Waldspurger <redacted> Reviewed-by: Jonathan Davies <redacted> --- Documentation/admin-guide/mm/pagemap.rst | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
index fb578fbbb76c..627f3832b3a2 100644
--- a/Documentation/admin-guide/mm/pagemap.rst
+++ b/Documentation/admin-guide/mm/pagemap.rst@@ -207,3 +207,9 @@ Before Linux 3.11 pagemap bits 55-60 were used for "page-shift" (which is always 12 at most architectures). Since Linux 3.11 their meaning changes after first clear of soft-dirty bits. Since Linux 4.2 they are used for flags unconditionally. + +Note that the page table entries for swappable and non-syncable pages are +cleared when those pages are zapped or swapped out. This makes information +about the page disappear from the pagemap. The location of the swapped +page can still be retrieved from the page cache, but flags like SOFT_DIRTY +and UFFD_WP are lost irretrievably.
--
2.32.0.380.geb27b338a3