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-rw-r--r--Documentation/sysctl/vm.txt30
1 files changed, 30 insertions, 0 deletions
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index f69895738357..dcc75a9ed919 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -18,6 +18,7 @@ files can be found in mm/swap.c.
Currently, these files are in /proc/sys/vm:
+- admin_reserve_kbytes
- block_dump
- compact_memory
- dirty_background_bytes
@@ -59,6 +60,35 @@ Currently, these files are in /proc/sys/vm:
==============================================================
+admin_reserve_kbytes
+
+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
block_dump enables block I/O debugging when set to a nonzero value. More