On Fri, Jul 26, 2019 at 01:17:10PM -0700, sspatil@google.com wrote:

Thanks Joel, just a couple of nits for the doc inline below. Other than that,

Reviewed-by: Sandeep Patil <redacted>

Thanks!

I'll plan on making changes to Android to use this instead of the pagemap +
page_idle. I think it will also be considerably faster.

Cool, glad to know.

On Fri, Jul 26, 2019 at 11:23:19AM -0400, Joel Fernandes (Google) wrote:

quoted

This patch updates the documentation with the new page_idle tracking
feature which uses virtual address indexing.

Signed-off-by: Joel Fernandes (Google) <redacted>
---
 .../admin-guide/mm/idle_page_tracking.rst     | 43 ++++++++++++++++---
 1 file changed, 36 insertions(+), 7 deletions(-)

diff --git a/Documentation/admin-guide/mm/idle_page_tracking.rst b/Documentation/admin-guide/mm/idle_page_tracking.rst
index df9394fb39c2..1eeac78c94a7 100644
--- a/Documentation/admin-guide/mm/idle_page_tracking.rst
+++ b/Documentation/admin-guide/mm/idle_page_tracking.rst

@@ -19,10 +19,14 @@ It is enabled by CONFIG_IDLE_PAGE_TRACKING=y.
 
 User API
 ========
+There are 2 ways to access the idle page tracking API. One uses physical
+address indexing, another uses a simpler virtual address indexing scheme.
 
-The idle page tracking API is located at ``/sys/kernel/mm/page_idle``.
-Currently, it consists of the only read-write file,
-``/sys/kernel/mm/page_idle/bitmap``.
+Physical address indexing
+-------------------------
+The idle page tracking API for physical address indexing using page frame
+numbers (PFN) is located at ``/sys/kernel/mm/page_idle``.  Currently, it
+consists of the only read-write file, ``/sys/kernel/mm/page_idle/bitmap``.
 
 The file implements a bitmap where each bit corresponds to a memory page. The
 bitmap is represented by an array of 8-byte integers, and the page at PFN #i is

@@ -74,6 +78,31 @@ See :ref:`Documentation/admin-guide/mm/pagemap.rst <pagemap>` for more
 information about ``/proc/pid/pagemap``, ``/proc/kpageflags``, and
 ``/proc/kpagecgroup``.
 
+Virtual address indexing
+------------------------
+The idle page tracking API for virtual address indexing using virtual page
+frame numbers (VFN) is located at ``/proc/<pid>/page_idle``. It is a bitmap
+that follows the same semantics as ``/sys/kernel/mm/page_idle/bitmap``
+except that it uses virtual instead of physical frame numbers.
+
+This idle page tracking API does not need deal with PFN so it does not require

s/need//

quoted

+prior lookups of ``pagemap`` in order to find if page is idle or not. This is

s/in order to find if page is idle or not//

Fixed both, thank you! Will send out update soon.

thanks,

 - Joel