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| author | Andrew Shewmaker <agshew@gmail.com> | 2013-04-30 02:08:11 +0400 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-04-30 02:54:36 +0400 |
| commit | 4eeab4f5580d11bffedc697684b91b0bca0d5009 (patch) | |
| tree | 4e9a0c010d34e786df52225039a17aa38e9adf17 /Documentation/sysctl | |
| parent | c9b1d0981fcce3d9976d7b7a56e4e0503bc610dd (diff) | |
| download | linux-4eeab4f5580d11bffedc697684b91b0bca0d5009.tar.xz | |
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.
[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: make init_admin_reserve() static]
Signed-off-by: Andrew Shewmaker <agshew@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/sysctl')
| -rw-r--r-- | Documentation/sysctl/vm.txt | 30 |
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 |