On Thu, 1 Sep 2011 15:26:50 -0400
Rik van Riel <riel@xxxxxxxxxx> wrote:
> Add a userspace visible knob to tell the VM to keep an extra amount
> of memory free, by increasing the gap between each zone's min and
> low watermarks.
>
> This is useful for realtime applications that call system
> calls and have a bound on the number of allocations that happen
> in any short time period. In this application, extra_free_kbytes
> would be left at an amount equal to or larger than than the
> maximum number of allocations that happen in any burst.
>
> It may also be useful to reduce the memory use of virtual
> machines (temporarily?), in a way that does not cause memory
> fragmentation like ballooning does.
>
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -96,6 +96,7 @@ extern char core_pattern[];
> extern unsigned int core_pipe_limit;
> extern int pid_max;
> extern int min_free_kbytes;
> +extern int extra_free_kbytes;
No externs in C, please. Feel free to fix min_free_kbytes while you're
there ;)
swap.h is a common place to declare these things. mmzone.h would make
sense too.
> extern int pid_max_min, pid_max_max;
> extern int sysctl_drop_caches;
> extern int percpu_pagelist_fraction;
> @@ -1189,6 +1190,14 @@ static struct ctl_table vm_table[] = {
> .extra1 = &zero,
> },
> {
> + .procname = "extra_free_kbytes",
> + .data = &extra_free_kbytes,
> + .maxlen = sizeof(extra_free_kbytes),
> + .mode = 0644,
> + .proc_handler = min_free_kbytes_sysctl_handler,
Lazy. The function should be renamed to accurately reflect its role.
> + .extra1 = &zero,
> + },
> + {
> .procname = "percpu_pagelist_fraction",
> .data = &percpu_pagelist_fraction,
> .maxlen = sizeof(percpu_pagelist_fraction),
>
> ...
>
> +int extra_free_kbytes = 0;
I'm inclined to agree with checkpatch here - it's just noise.
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