|author||Andrew Shewmaker <email@example.com>||2013-04-29 15:08:11 -0700|
|committer||Linus Torvalds <firstname.lastname@example.org>||2013-04-29 15:54:36 -0700|
mm: replace hardcoded 3% with admin_reserve_pages knob
Add an admin_reserve_kbytes knob to allow admins to change the hardcoded memory reserve to something other than 3%, which may be multiple gigabytes on large memory systems. Only about 8MB is necessary to enable recovery in the default mode, and only a few hundred MB are required even when overcommit is disabled. This affects OVERCOMMIT_GUESS and OVERCOMMIT_NEVER. admin_reserve_kbytes is initialized to min(3% free pages, 8MB) I arrived at 8MB by summing the RSS of sshd or login, bash, and top. Please see first patch in this series for full background, motivation, testing, and full changelog. [email@example.com: coding-style fixes] [firstname.lastname@example.org: make init_admin_reserve() static] Signed-off-by: Andrew Shewmaker <email@example.com> Signed-off-by: Andrew Morton <firstname.lastname@example.org> Signed-off-by: Linus Torvalds <email@example.com>
Diffstat (limited to 'Documentation/sysctl')
1 files changed, 30 insertions, 0 deletions
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index f69895738357..dcc75a9ed919 100644
@@ -18,6 +18,7 @@ files can be found in mm/swap.c.
Currently, these files are in /proc/sys/vm:
@@ -59,6 +60,35 @@ Currently, these files are in /proc/sys/vm:
+The amount of free memory in the system that should be reserved for users
+with the capability cap_sys_admin.
+admin_reserve_kbytes defaults to min(3% of free pages, 8MB)
+That should provide enough for the admin to log in and kill a process,
+if necessary, under the default overcommit 'guess' mode.
+Systems running under overcommit 'never' should increase this to account
+for the full Virtual Memory Size of programs used to recover. Otherwise,
+root may not be able to log in to recover the system.
+How do you calculate a minimum useful reserve?
+sshd or login + bash (or some other shell) + top (or ps, kill, etc.)
+For overcommit 'guess', we can sum resident set sizes (RSS).
+On x86_64 this is about 8MB.
+For overcommit 'never', we can take the max of their virtual sizes (VSZ)
+and add the sum of their RSS.
+On x86_64 this is about 128MB.
+Changing this takes effect whenever an application requests memory.
block_dump enables block I/O debugging when set to a nonzero value. More