[PATCH] Document interaction between compaction and the unevictable LRU

[Eric B Munson]

The memory compaction code uses the migration code to do most of the
work in compaction.  However, the compaction code interacts with the
unevictable LRU differently than migration code and this difference
should be noted in the documentation.

Signed-off-by: Eric B Munson <emunson@xxxxxxxxxx>
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 Documentation/vm/unevictable-lru.txt |   11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/Documentation/vm/unevictable-lru.txt b/Documentation/vm/unevictable-lru.txt
index 744f82f..b72246e 100644
--- a/Documentation/vm/unevictable-lru.txt
+++ b/Documentation/vm/unevictable-lru.txt
@@ -22,6 +22,7 @@ CONTENTS
      - Filtering special vmas.
      - munlock()/munlockall() system call handling.
      - Migrating mlocked pages.
+     - Compacting mlocked pages.
      - mmap(MAP_LOCKED) system call handling.
      - munmap()/exit()/exec() system call handling.
      - try_to_unmap().
@@ -450,6 +451,16 @@ list because of a race between munlock and migration, page migration uses the
 putback_lru_page() function to add migrated pages back to the LRU.
 
 
+COMPACTING MLOCKED PAGES
+------------------------
+
+The unevictable LRU can be scanned for compactable regions and the default
+behavior is to do so.  There is a sysctl to control this behavior (see
+Documentation/sysctl/vm.txt).  Once scanning of the unevictable LRU is
+enabled, the work of compaction is mostly handled by the page migration code
+and the same work flow as described in MIGRATING MLOCKED PAGES will apply.
+
+
 mmap(MAP_LOCKED) SYSTEM CALL HANDLING
 -------------------------------------
 
-- 
1.7.9.5

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