[PATCH] Documentation/vm/pagemap.txt: document bit WAITERS

From: Konstantin Khlebnikov
Date: Sat Feb 17 2018 - 03:15:56 EST


Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
---
Documentation/vm/pagemap.txt | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt
index eafcefa15261..eaa46771fa30 100644
--- a/Documentation/vm/pagemap.txt
+++ b/Documentation/vm/pagemap.txt
@@ -71,6 +71,7 @@ There are four components to pagemap:
23. BALLOON
24. ZERO_PAGE
25. IDLE
+ 26. WAITERS

* /proc/kpagecgroup. This file contains a 64-bit inode number of the
memory cgroup each page is charged to, indexed by PFN. Only available when
@@ -127,6 +128,13 @@ Short descriptions to the page flags:
stale in case the page was accessed via a PTE. To make sure the flag
is up-to-date one has to read /sys/kernel/mm/page_idle/bitmap first.

+26. WAITERS
+ Indicates tasks are waiting when bits LOCKED or WRITEBACK will be cleared.
+ They might be blocked by undergoing IO or by contention on page lock.
+ Bit WAITERS might be false-positive, in this case next clear of LOCKED or
+ WRITEBACK will clear WAITERS too. I.e. without LOCKED and WRITEBACK it's
+ false-positive for sure.
+
[IO related page flags]
1. ERROR IO error occurred
3. UPTODATE page has up-to-date data