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| author | Pavel Emelyanov | 2013-07-04 00:01:20 +0200 |
|---|---|---|
| committer | Linus Torvalds | 2013-07-04 01:07:26 +0200 |
| commit | 0f8975ec4db2c8b5bd111b211292ca9be0feb6b8 (patch) | |
| tree | 47bb0acc9fc3e783ad9cf33097a6636190f5e42b /arch/x86/Kconfig | |
| parent | pagemap: introduce pagemap_entry_t without pmshift bits (diff) | |
| download | kernel-qcow2-linux-0f8975ec4db2c8b5bd111b211292ca9be0feb6b8.tar.gz kernel-qcow2-linux-0f8975ec4db2c8b5bd111b211292ca9be0feb6b8.tar.xz kernel-qcow2-linux-0f8975ec4db2c8b5bd111b211292ca9be0feb6b8.zip | |
mm: soft-dirty bits for user memory changes tracking
The soft-dirty is a bit on a PTE which helps to track which pages a task
writes to. In order to do this tracking one should
1. Clear soft-dirty bits from PTEs ("echo 4 > /proc/PID/clear_refs)
2. Wait some time.
3. Read soft-dirty bits (55'th in /proc/PID/pagemap2 entries)
To do this tracking, the writable bit is cleared from PTEs when the
soft-dirty bit is. Thus, after this, when the task tries to modify a
page at some virtual address the #PF occurs and the kernel sets the
soft-dirty bit on the respective PTE.
Note, that although all the task's address space is marked as r/o after
the soft-dirty bits clear, the #PF-s that occur after that are processed
fast. This is so, since the pages are still mapped to physical memory,
and thus all the kernel does is finds this fact out and puts back
writable, dirty and soft-dirty bits on the PTE.
Another thing to note, is that when mremap moves PTEs they are marked
with soft-dirty as well, since from the user perspective mremap modifies
the virtual memory at mremap's new address.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Glauber Costa <glommer@parallels.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch/x86/Kconfig')
| -rw-r--r-- | arch/x86/Kconfig | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index b094816a7e0f..10764a3d62cc 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -102,6 +102,7 @@ config X86 select HAVE_ARCH_SECCOMP_FILTER select BUILDTIME_EXTABLE_SORT select GENERIC_CMOS_UPDATE + select HAVE_ARCH_SOFT_DIRTY select CLOCKSOURCE_WATCHDOG select GENERIC_CLOCKEVENTS select ARCH_CLOCKSOURCE_DATA if X86_64 |