[PATCH] Docs/mm/damon/design: describe the differences for pageout's virtual address and physcial address

[Barry Song]

From: Barry Song <v-songbaohua@xxxxxxxx>

The doc needs update. As only in the case of virtual address, we are
calling madvise() with MADV_PAGEOUT; but in the case of physical
address, we are actually calling reclaim_pages() directly. And
madvise() with MADV_PAGEOUT is much more aggresive on reclamation
compared to reclaim_pages() on paddr.

Cc: SeongJae Park <sj@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
---
 Documentation/mm/damon/design.rst | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
index 8c89d26f0baa..6c50743552f5 100644
--- a/Documentation/mm/damon/design.rst
+++ b/Documentation/mm/damon/design.rst
@@ -315,7 +315,13 @@ that supports each action are as below.
    Supported by ``vaddr`` and ``fvaddr`` operations set.
  - ``cold``: Call ``madvise()`` for the region with ``MADV_COLD``.
    Supported by ``vaddr`` and ``fvaddr`` operations set.
- - ``pageout``: Call ``madvise()`` for the region with ``MADV_PAGEOUT``.
+ - ``pageout``: Call ``madvise()`` for the region with ``MADV_PAGEOUT`` if
+   the region is using virtual address; otherwise, call ``reclaim_pages()``
+   for the region if physical address is used.
+   ``madvise()``  with ``MADV_PAGEOUT``  is aggressively reclaiming memory
+   when pages are not shared by multiple processes. Differently, paddr's
+   pageout  will do the best-effort reclamation by scanning PTEs to figure
+   out if pages are young, if not, pages are reclaimed.
    Supported by ``vaddr``, ``fvaddr`` and ``paddr`` operations set.
  - ``hugepage``: Call ``madvise()`` for the region with ``MADV_HUGEPAGE``.
    Supported by ``vaddr`` and ``fvaddr`` operations set.
-- 
2.34.1