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authorJosé Pekkarinen <jose.pekkarinen@nokia.com>2016-04-11 10:41:07 +0300
committerJosé Pekkarinen <jose.pekkarinen@nokia.com>2016-04-13 08:17:18 +0300
commite09b41010ba33a20a87472ee821fa407a5b8da36 (patch)
treed10dc367189862e7ca5c592f033dc3726e1df4e3 /kernel/Documentation/vm/pagemap.txt
parentf93b97fd65072de626c074dbe099a1fff05ce060 (diff)
These changes are the raw update to linux-4.4.6-rt14. Kernel sources
are taken from kernel.org, and rt patch from the rt wiki download page. During the rebasing, the following patch collided: Force tick interrupt and get rid of softirq magic(I70131fb85). Collisions have been removed because its logic was found on the source already. Change-Id: I7f57a4081d9deaa0d9ccfc41a6c8daccdee3b769 Signed-off-by: José Pekkarinen <jose.pekkarinen@nokia.com>
Diffstat (limited to 'kernel/Documentation/vm/pagemap.txt')
-rw-r--r--kernel/Documentation/vm/pagemap.txt28
1 files changed, 25 insertions, 3 deletions
diff --git a/kernel/Documentation/vm/pagemap.txt b/kernel/Documentation/vm/pagemap.txt
index 6bfbc172c..0e1e55588 100644
--- a/kernel/Documentation/vm/pagemap.txt
+++ b/kernel/Documentation/vm/pagemap.txt
@@ -5,7 +5,7 @@ pagemap is a new (as of 2.6.25) set of interfaces in the kernel that allow
userspace programs to examine the page tables and related information by
reading files in /proc.
-There are three components to pagemap:
+There are four components to pagemap:
* /proc/pid/pagemap. This file lets a userspace process find out which
physical frame each virtual page is mapped to. It contains one 64-bit
@@ -16,11 +16,17 @@ There are three components to pagemap:
* Bits 0-4 swap type if swapped
* Bits 5-54 swap offset if swapped
* Bit 55 pte is soft-dirty (see Documentation/vm/soft-dirty.txt)
- * Bits 56-60 zero
- * Bit 61 page is file-page or shared-anon
+ * Bit 56 page exclusively mapped (since 4.2)
+ * Bits 57-60 zero
+ * Bit 61 page is file-page or shared-anon (since 3.5)
* Bit 62 page swapped
* Bit 63 page present
+ Since Linux 4.0 only users with the CAP_SYS_ADMIN capability can get PFNs.
+ In 4.0 and 4.1 opens by unprivileged fail with -EPERM. Starting from
+ 4.2 the PFN field is zeroed if the user does not have CAP_SYS_ADMIN.
+ Reason: information about PFNs helps in exploiting Rowhammer vulnerability.
+
If the page is not present but in swap, then the PFN contains an
encoding of the swap file number and the page's offset into the
swap. Unmapped pages return a null PFN. This allows determining
@@ -64,6 +70,11 @@ There are three components to pagemap:
22. THP
23. BALLOON
24. ZERO_PAGE
+ 25. IDLE
+
+ * /proc/kpagecgroup. This file contains a 64-bit inode number of the
+ memory cgroup each page is charged to, indexed by PFN. Only available when
+ CONFIG_MEMCG is set.
Short descriptions to the page flags:
@@ -110,6 +121,12 @@ Short descriptions to the page flags:
24. ZERO_PAGE
zero page for pfn_zero or huge_zero page
+25. IDLE
+ page has not been accessed since it was marked idle (see
+ Documentation/vm/idle_page_tracking.txt). Note that this flag may be
+ stale in case the page was accessed via a PTE. To make sure the flag
+ is up-to-date one has to read /sys/kernel/mm/page_idle/bitmap first.
+
[IO related page flags]
1. ERROR IO error occurred
3. UPTODATE page has up-to-date data
@@ -159,3 +176,8 @@ Other notes:
Reading from any of the files will return -EINVAL if you are not starting
the read on an 8-byte boundary (e.g., if you sought an odd number of bytes
into the file), or if the size of the read is not a multiple of 8 bytes.
+
+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.