docs: mm: clarify that user_reserve_kbytes has no effect when overcommit_memory is set to 0 or 1

Looking at __vm_enough_memory() in mm/util.c, user_reserve_kbytes has no
effect when overcommit_memory is set to 0 or 1. The documentation for
overcommit_memory already references user_reserve_kbytes when the flag
is set to 2.

Let's go ahead and add a clarification to user_reserve_kbytes in vm.rst
that it has no effect when overcommit_memory is set to 0 or 1.

Link: https://lore.kernel.org/20260528-mm-clarify-docs-v1-1-aa88e83b4bfd@redhat.com
Signed-off-by: Brian Masney <bmasney@redhat.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
index 97e12359775c..b9b0c218bfb4 100644
--- a/Documentation/admin-guide/sysctl/vm.rst
+++ b/Documentation/admin-guide/sysctl/vm.rst
@@ -1034,6 +1034,8 @@ min(3% of current process size, user_reserve_kbytes) of free memory.
 This is intended to prevent a user from starting a single memory hogging
 process, such that they cannot recover (kill the hog).
 
+This setting has no effect when overcommit_memory is set to 0 or 1.
+
 user_reserve_kbytes defaults to min(3% of the current process size, 128MB).
 
 If this is reduced to zero, then the user will be allowed to allocate