diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/sysctl/vm.txt | 20 | ||||
| -rw-r--r-- | Documentation/vm/overcommit-accounting | 8 |
2 files changed, 27 insertions, 1 deletions
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt index 078701fdbd4d..f69895738357 100644 --- a/Documentation/sysctl/vm.txt +++ b/Documentation/sysctl/vm.txt @@ -53,6 +53,7 @@ Currently, these files are in /proc/sys/vm: - percpu_pagelist_fraction - stat_interval - swappiness +- user_reserve_kbytes - vfs_cache_pressure - zone_reclaim_mode @@ -542,6 +543,7 @@ memory until it actually runs out. When this flag is 2, the kernel uses a "never overcommit" policy that attempts to prevent any overcommit of memory. +Note that user_reserve_kbytes affects this policy. This feature can be very useful because there are a lot of programs that malloc() huge amounts of memory "just-in-case" @@ -645,6 +647,24 @@ The default value is 60. ============================================================== +- user_reserve_kbytes + +When overcommit_memory is set to 2, "never overommit" mode, reserve +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). + +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 +all free memory with a single process, minus admin_reserve_kbytes. +Any subsequent attempts to execute a command will result in +"fork: Cannot allocate memory". + +Changing this takes effect whenever an application requests memory. + +============================================================== + vfs_cache_pressure ------------------ diff --git a/Documentation/vm/overcommit-accounting b/Documentation/vm/overcommit-accounting index 706d7ed9d8d2..8eaa2fc4b8fa 100644 --- a/Documentation/vm/overcommit-accounting +++ b/Documentation/vm/overcommit-accounting @@ -8,7 +8,9 @@ The Linux kernel supports the following overcommit handling modes default. 1 - Always overcommit. Appropriate for some scientific - applications. + applications. Classic example is code using sparse arrays + and just relying on the virtual memory consisting almost + entirely of zero pages. 2 - Don't overcommit. The total address space commit for the system is not permitted to exceed swap + a @@ -18,6 +20,10 @@ The Linux kernel supports the following overcommit handling modes pages but will receive errors on memory allocation as appropriate. + Useful for applications that want to guarantee their + memory allocations will be available in the future + without having to initialize every page. + The overcommit policy is set via the sysctl `vm.overcommit_memory'. The overcommit percentage is set via `vm.overcommit_ratio'. |