Linux-libre 4.8.2-gnupck-4.8.2-gnu

1 files changed, 22 insertions, 1 deletions

diff --git a/Documentation/vm/unevictable-lru.txt b/Documentation/vm/unevictable-lru.txt
index fa3b52708..e14718572 100644
--- a/Documentation/vm/unevictable-lru.txt
+++ b/Documentation/vm/unevictable-lru.txt
@@ -122,7 +122,7 @@ MEMORY CONTROL GROUP INTERACTION
 --------------------------------
 
 The unevictable LRU facility interacts with the memory control group [aka
-memory controller; see Documentation/cgroups/memory.txt] by extending the
+memory controller; see Documentation/cgroup-v1/memory.txt] by extending the
 lru_list enum.
 
 The memory controller data structure automatically gets a per-zone unevictable
@@ -461,6 +461,27 @@ 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.
 
+MLOCKING TRANSPARENT HUGE PAGES
+-------------------------------
+
+A transparent huge page is represented by a single entry on an LRU list.
+Therefore, we can only make unevictable an entire compound page, not
+individual subpages.
+
+If a user tries to mlock() part of a huge page, we want the rest of the
+page to be reclaimable.
+
+We cannot just split the page on partial mlock() as split_huge_page() can
+fail and new intermittent failure mode for the syscall is undesirable.
+
+We handle this by keeping PTE-mapped huge pages on normal LRU lists: the
+PMD on border of VM_LOCKED VMA will be split into PTE table.
+
+This way the huge page is accessible for vmscan. Under memory pressure the
+page will be split, subpages which belong to VM_LOCKED VMAs will be moved
+to unevictable LRU and the rest can be reclaimed.
+
+See also comment in follow_trans_huge_pmd().
 
 mmap(MAP_LOCKED) SYSTEM CALL HANDLING
 -------------------------------------