The patch titled
Subject: mm: better document PG_reserved
has been added to the -mm tree. Its filename is
mm-better-document-pg_reserved.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-better-document-pg_reserved.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-better-document-pg_reserved.patch
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm: better document PG_reserved
The usage of PG_reserved and how PG_reserved pages are to be treated is
buried deep down in different parts of the kernel. Let's shine some light
onto these details by documenting current users and expected behavior.
Especially, clarify on the "Some of them might not even exist" case.
These are physical memory gaps that will never be dumped as they are not
marked as IORESOURCE_SYSRAM. PG_reserved does in general not hinder
anybody from dumping or swapping. In some cases, these pages will not be
stored in the hibernation image.
Link: http://lkml.kernel.org/r/20190114125903.24845-10-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Anthony Yznaga <anthony.yznaga@xxxxxxxxxx>
Cc: Miles Chen <miles.chen@xxxxxxxxxxxx>
Cc: <yi.z.zhang@xxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/page-flags.h | 33 +++++++++++++++++++++++++++++++--
1 file changed, 31 insertions(+), 2 deletions(-)
--- a/include/linux/page-flags.h~mm-better-document-pg_reserved
+++ a/include/linux/page-flags.h
@@ -17,8 +17,37 @@
/*
* 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. The "struct page" of such a page
+ * should in general not be touched (e.g. set dirty) except by its owner.
+ * Pages marked as PG_reserved include:
+ * - Pages part of the kernel image (including vDSO) and similar (e.g. BIOS,
+ * initrd, HW tables)
+ * - Pages reserved or allocated early during boot (before the page allocator
+ * was initialized). This includes (depending on the architecture) the
+ * initial vmemmap, initial page tables, crashkernel, elfcorehdr, and much
+ * much more. Once (if ever) freed, PG_reserved is cleared and they will
+ * be given to the page allocator.
+ * - Pages falling into physical memory gaps - not IORESOURCE_SYSRAM. Trying
+ * to read/write these pages might end badly. Don't touch!
+ * - The zero page(s)
+ * - Pages not added to the page allocator when onlining a section because
+ * they were excluded via the online_page_callback() or because they are
+ * PG_hwpoison.
+ * - Pages allocated in the context of kexec/kdump (loaded kernel image,
+ * control pages, vmcoreinfo)
+ * - MMIO/DMA pages. Some architectures don't allow to ioremap pages that are
+ * not marked PG_reserved (as they might be in use by somebody else who does
+ * not respect the caching strategy).
+ * - Pages part of an offline section (struct pages of offline sections should
+ * not be trusted as they will be initialized when first onlined).
+ * - MCA pages on ia64
+ * - Pages holding CPU notes for POWER Firmware Assisted Dump
+ * - Device memory (e.g. PMEM, DAX, HMM)
+ * Some PG_reserved pages will be excluded from the hibernation image.
+ * PG_reserved does in general not hinder anybody from dumping or swapping
+ * and is no longer required for remap_pfn_range(). ioremap might require it.
+ * Consequently, PG_reserved for a page mapped into user space can indicate
+ * the zero page, the vDSO, MMIO pages or device memory.
*
* 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-balloon-update-comment-about-isolation-migration-compaction.patch
mm-convert-pg_balloon-to-pg_offline.patch
kexec-export-pg_offline-to-vmcoreinfo.patch
xen-balloon-mark-inflated-pages-pg_offline.patch
hv_balloon-mark-inflated-pages-pg_offline.patch
vmw_balloon-mark-inflated-pages-pg_offline.patch
vmw_balloon-mark-inflated-pages-pg_offline-v2.patch
pm-hibernate-use-pfn_to_online_page.patch
pm-hibernate-exclude-all-pageoffline-pages.patch
pm-hibernate-exclude-all-pageoffline-pages-v2.patch
agp-efficeon-no-need-to-set-pg_reserved-on-gatt-tables.patch
s390-vdso-dont-clear-pg_reserved.patch
powerpc-vdso-dont-clear-pg_reserved.patch
riscv-vdso-dont-clear-pg_reserved.patch
m68k-mm-use-__clearpagereserved.patch
arm64-kexec-no-need-to-clearpagereserved.patch
arm64-kdump-no-need-to-mark-crashkernel-pages-manually-pg_reserved.patch
ia64-perfmon-dont-mark-buffer-pages-as-pg_reserved.patch
mm-better-document-pg_reserved.patch
