From: Joel Savitz <jsavitz@redhat.com>
Date: Fri, 29 Apr 2022 06:16:01 +0000 (-0700)
Subject: Documentation/sysctl: document page_lock_unfairness
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=8d98e42fb20c25e8efdab4cc1ac46d52ba964aca;p=linux.git

Documentation/sysctl: document page_lock_unfairness

commit 5ef64cc8987a ("mm: allow a controlled amount of unfairness in the
page lock") introduced a new systctl but no accompanying documentation.

Add a simple entry to the documentation.

Link: https://lkml.kernel.org/r/20220325164437.120246-1-jsavitz@redhat.com
Signed-off-by: Joel Savitz <jsavitz@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: "zhangyi (F)" <yi.zhang@huawei.com>
Cc: Charan Teja Reddy <charante@codeaurora.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
index f4804ce37c58b..747e325ebcd0c 100644
--- a/Documentation/admin-guide/sysctl/vm.rst
+++ b/Documentation/admin-guide/sysctl/vm.rst
@@ -62,6 +62,7 @@ Currently, these files are in /proc/sys/vm:
 - overcommit_memory
 - overcommit_ratio
 - page-cluster
+- page_lock_unfairness
 - panic_on_oom
 - percpu_pagelist_high_fraction
 - stat_interval
@@ -754,6 +755,14 @@ extra faults and I/O delays for following faults if they would have been part of
 that consecutive pages readahead would have brought in.
 
 
+page_lock_unfairness
+====================
+
+This value determines the number of times that the page lock can be
+stolen from under a waiter. After the lock is stolen the number of times
+specified in this file (default is 5), the "fair lock handoff" semantics
+will apply, and the waiter will only be awakened if the lock can be taken.
+
 panic_on_oom
 ============