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

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Date: Sun, 25 Feb 2024 10:50:23 +1300
From: Barry Song <21cnbao@...il.com>
To: corbet@....net,
	linux-mm@...ck.org,
	akpm@...ux-foundation.org,
	damon@...ts.linux.dev,
	linux-doc@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Barry Song <v-songbaohua@...o.com>,
	SeongJae Park <sj@...nel.org>,
	Minchan Kim <minchan@...nel.org>,
	Michal Hocko <mhocko@...e.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: [PATCH] Docs/mm/damon/design: describe the differences for pageout's virtual address and physcial address

From: Barry Song <v-songbaohua@...o.com>

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@...nel.org>
Cc: Minchan Kim <minchan@...nel.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Signed-off-by: Barry Song <v-songbaohua@...o.com>
---
 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