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

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Date:   Sat, 17 Feb 2018 11:15:43 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] Documentation/vm/pagemap.txt: document bit WAITERS

Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
---
 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