€•^&      Œsphinx.addnodes”Œdocument”“”)”}”(Œ	rawsource”Œ ”Œchildren”]”(Œtranslations”ŒLanguagesNode”“”)”}”(hhh]”(h Œpending_xref”“”)”}”(hhh]”Œdocutils.nodes”ŒText”“”ŒChinese (Simplified)”…””}”Œparent”hsbaŒ
attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ	refdomain”Œstd”Œreftype”Œdoc”Œ	reftarget”Œ-/translations/zh_CN/admin-guide/mm/soft-dirty”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ-/translations/zh_TW/admin-guide/mm/soft-dirty”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ-/translations/it_IT/admin-guide/mm/soft-dirty”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ-/translations/ja_JP/admin-guide/mm/soft-dirty”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ-/translations/ko_KR/admin-guide/mm/soft-dirty”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ-/translations/sp_SP/admin-guide/mm/soft-dirty”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒSoft-Dirty PTEs”h]”hŒSoft-Dirty PTEs”…””}”(hh¨hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hh£hžhhŸŒG/var/lib/git/docbuild/linux/Documentation/admin-guide/mm/soft-dirty.rst”h KubhŒ	paragraph”“”)”}”(hŒ{The soft-dirty is a bit on a PTE which helps to track which pages a task
writes to. In order to do this tracking one should”h]”hŒ{The soft-dirty is a bit on a PTE which helps to track which pages a task
writes to. In order to do this tracking one should”…””}”(hh¹hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubhŒblock_quote”“”)”}”(hX  1. Clear soft-dirty bits from the task's PTEs.

   This is done by writing "4" into the ``/proc/PID/clear_refs`` file of the
   task in question.

2. Wait some time.

3. Read soft-dirty bits from the PTEs.

   This is done by reading from the ``/proc/PID/pagemap``. The bit 55 of the
   64-bit qword is the soft-dirty one. If set, the respective PTE was
   written to since step 1.

”h]”hŒenumerated_list”“”)”}”(hhh]”(hŒ	list_item”“”)”}”(hŒ‰Clear soft-dirty bits from the task's PTEs.

This is done by writing "4" into the ``/proc/PID/clear_refs`` file of the
task in question.
”h]”(h¸)”}”(hŒ+Clear soft-dirty bits from the task's PTEs.”h]”hŒ-Clear soft-dirty bits from the taskâ€™s PTEs.”…””}”(hhØhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KhhÔubh¸)”}”(hŒ[This is done by writing "4" into the ``/proc/PID/clear_refs`` file of the
task in question.”h]”(hŒ)This is done by writing â€œ4â€ into the ”…””}”(hhæhžhhŸNh NubhŒliteral”“”)”}”(hŒ``/proc/PID/clear_refs``”h]”hŒ/proc/PID/clear_refs”…””}”(hhðhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hîhhæubhŒ file of the
task in question.”…””}”(hhæhžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K
hhÔubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÒhhÏubhÓ)”}”(hŒWait some time.
”h]”h¸)”}”(hŒWait some time.”h]”hŒWait some time.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hÒhhÏubhÓ)”}”(hŒÌRead soft-dirty bits from the PTEs.

This is done by reading from the ``/proc/PID/pagemap``. The bit 55 of the
64-bit qword is the soft-dirty one. If set, the respective PTE was
written to since step 1.

”h]”(h¸)”}”(hŒ#Read soft-dirty bits from the PTEs.”h]”hŒ#Read soft-dirty bits from the PTEs.”…””}”(hj*  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khj&  ubh¸)”}”(hŒ¥This is done by reading from the ``/proc/PID/pagemap``. The bit 55 of the
64-bit qword is the soft-dirty one. If set, the respective PTE was
written to since step 1.”h]”(hŒ!This is done by reading from the ”…””}”(hj8  hžhhŸNh Nubhï)”}”(hŒ``/proc/PID/pagemap``”h]”hŒ/proc/PID/pagemap”…””}”(hj@  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hîhj8  ubhŒo. The bit 55 of the
64-bit qword is the soft-dirty one. If set, the respective PTE was
written to since step 1.”…””}”(hj8  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khj&  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1hÒhhÏubeh}”(h]”h ]”h"]”h$]”h&]”Œenumtype”Œarabic”Œprefix”hŒsuffix”Œ.”uh1hÍhhÉubah}”(h]”h ]”h"]”h$]”h&]”uh1hÇhŸh¶h Khh£hžhubh¸)”}”(hX  Internally, to do this tracking, the writable bit is cleared from PTEs
when the soft-dirty bit is cleared. So, 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.”h]”hX  Internally, to do this tracking, the writable bit is cleared from PTEs
when the soft-dirty bit is cleared. So, 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.”…””}”(hjo  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hXB  Note, that although all the task's address space is marked as r/o after the
soft-dirty bits clear, the #PF-s that occur after that are processed fast.
This is so, since the pages are still mapped to physical memory, and thus all
the kernel does is finds this fact out and puts both writable and soft-dirty
bits on the PTE.”h]”hXD  Note, that although all the taskâ€™s address space is marked as r/o after the
soft-dirty bits clear, the #PF-s that occur after that are processed fast.
This is so, since the pages are still mapped to physical memory, and thus all
the kernel does is finds this fact out and puts both writable and soft-dirty
bits on the PTE.”…””}”(hj}  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hXÕ  While in most cases tracking memory changes by #PF-s is more than enough
there is still a scenario when we can lose soft dirty bits -- a task
unmaps a previously mapped memory region and then maps a new one at exactly
the same place. When unmap is called, the kernel internally clears PTE values
including soft dirty bits. To notify user space application about such
memory region renewal the kernel always marks new memory regions (and
expanded regions) as soft dirty.”h]”hXÕ  While in most cases tracking memory changes by #PF-s is more than enough
there is still a scenario when we can lose soft dirty bits -- a task
unmaps a previously mapped memory region and then maps a new one at exactly
the same place. When unmap is called, the kernel internally clears PTE values
including soft dirty bits. To notify user space application about such
memory region renewal the kernel always marks new memory regions (and
expanded regions) as soft dirty.”…””}”(hj‹  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K!hh£hžhubh¸)”}”(hŒvThis feature is actively used by the checkpoint-restore project. You
can find more details about it on http://criu.org”h]”(hŒgThis feature is actively used by the checkpoint-restore project. You
can find more details about it on ”…””}”(hj™  hžhhŸNh NubhŒ	reference”“”)”}”(hŒhttp://criu.org”h]”hŒhttp://criu.org”…””}”(hj£  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”Œrefuri”j¥  uh1j¡  hj™  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K)hh£hžhubh¸)”}”(hŒ-- Pavel Emelyanov, Apr 9, 2013”h]”hŒ-- Pavel Emelyanov, Apr 9, 2013”…””}”(hj¸  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K-hh£hžhubeh}”(h]”Œsoft-dirty-ptes”ah ]”h"]”Œsoft-dirty ptes”ah$]”h&]”uh1h¡hhhžhhŸh¶h Kubeh}”(h]”h ]”h"]”h$]”h&]”Œsource”h¶uh1hŒcurrent_source”NŒcurrent_line”NŒsettings”Œdocutils.frontend”ŒValues”“”)”}”(h¦NŒ	generator”NŒ	datestamp”NŒsource_link”NŒ
source_url”NŒtoc_backlinks”Œentry”Œfootnote_backlinks”KŒsectnum_xform”KŒstrip_comments”NŒstrip_elements_with_classes”NŒstrip_classes”NŒreport_level”KŒ
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id_counter”Œcollections”ŒCounter”“”}”…”R”Œparse_messages”]”Œtransform_messages”]”Œtransformer”NŒinclude_log”]”Œ
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