The patch titled
Subject: mm: clarify semantics of reserved pages
has been added to the -mm tree. Its filename is
mm-clarify-semantics-of-reserved-pages.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-clarify-semantics-of-reserved-pages.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-clarify-semantics-of-reserved-pages.patch
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm: clarify semantics of reserved pages
Patch series "mm/kdump: exclude reserved pages in dumps".
Dumping tools (like makedumpfile) right now don't exclude reserved pages.
So reserved pages might be access by dump tools although nobody except the
owner should touch them.
This is relevant in virtual environments where we soon might want to
report certain reserved pages to the hypervisor and they might no longer
be accessible - what already was documented for reserved pages a long time
ago ("might not even exist").
This patch (of 2):
The reserved bit once was used to hinder pages from getting swapped.
While this still works, the semantics are a little bit stronger nowadays:
The page should never be touched by anybody in the system except by the
owner. The original comment already gave a hint about that.
So especially, these pages should also not be dumped by dumping tools.
Let's make that more clear by updating the comment.
This will be useful especially in the future in virtual environments where
pages marked with the reserved bit might no longer be accessible.
Link: http://lkml.kernel.org/r/20180720123422.10127-2-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Miles Chen <miles.chen@xxxxxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: "Marc-André Lureau" <marcandre.lureau@xxxxxxxxxx>
Cc: Petr Tesarik <ptesarik@xxxxxxx>
Cc: Hari Bathini <hbathini@xxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/page-flags.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff -puN include/linux/page-flags.h~mm-clarify-semantics-of-reserved-pages include/linux/page-flags.h
--- a/include/linux/page-flags.h~mm-clarify-semantics-of-reserved-pages
+++ a/include/linux/page-flags.h
@@ -17,8 +17,8 @@
/*
* Various page->flags bits:
*
- * PG_reserved is set for special pages, which can never be swapped out. Some
- * of them might not even exist...
+ * PG_reserved is set for special pages, which should never be touched (read/
+ * write) by anybody except their owner. Some of them might not even exist.
*
* The PG_private bitflag is set on pagecache pages if they contain filesystem
* specific data (which is normally at page->private). It can be used by
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-clarify-semantics-of-reserved-pages.patch
kdump-include-pg_reserved-value-in-vmcoreinfo.patch
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