Commit 49f0ce5f authored by Jerome Marchand's avatar Jerome Marchand Committed by Linus Torvalds
Browse files

mm: add overcommit_kbytes sysctl variable 



Some applications that run on HPC clusters are designed around the
availability of RAM and the overcommit ratio is fine tuned to get the
maximum usage of memory without swapping.  With growing memory, the
1%-of-all-RAM grain provided by overcommit_ratio has become too coarse
for these workload (on a 2TB machine it represents no less than 20GB).

This patch adds the new overcommit_kbytes sysctl variable that allow a
much finer grain.

[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: fix nommu build]
Signed-off-by: default avatarJerome Marchand <jmarchan@redhat.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent aec6a888

Documentation/sysctl/vm.txt

+12 −0
Original line number Diff line number Diff line
@@ -47,6 +47,7 @@ Currently, these files are in /proc/sys/vm: 
- numa_zonelist_order

- oom_dump_tasks

- oom_kill_allocating_task

- overcommit_kbytes

- overcommit_memory

- overcommit_ratio

- page-cluster
@@ -574,6 +575,17 @@ The default value is 0. 


==============================================================



overcommit_kbytes:



When overcommit_memory is set to 2, the committed address space is not

permitted to exceed swap plus this amount of physical RAM. See below.



Note: overcommit_kbytes is the counterpart of overcommit_ratio. Only one

of them may be specified at a time. Setting one disables the other (which

then appears as 0 when read).



==============================================================



overcommit_memory:



This value contains a flag that enables memory overcommitment.

Documentation/vm/overcommit-accounting

+4 −3
Original line number Diff line number Diff line
@@ -14,8 +14,8 @@ The Linux kernel supports the following overcommit handling modes 


2	-	Don't overcommit. The total address space commit

		for the system is not permitted to exceed swap + a

		configurable percentage (default is 50) of physical RAM.

		Depending on the percentage you use, in most situations

		configurable amount (default is 50%) of physical RAM.

		Depending on the amount you use, in most situations

		this means a process will not be killed while accessing

		pages but will receive errors on memory allocation as

		appropriate.
@@ -26,7 +26,8 @@ The Linux kernel supports the following overcommit handling modes 


The overcommit policy is set via the sysctl `vm.overcommit_memory'.



The overcommit percentage is set via `vm.overcommit_ratio'.

The overcommit amount can be set via `vm.overcommit_ratio' (percentage)

or `vm.overcommit_kbytes' (absolute value).



The current overcommit limit and amount committed are viewable in

/proc/meminfo as CommitLimit and Committed_AS respectively.

include/linux/mm.h

+9 −0
Original line number Diff line number Diff line
@@ -57,6 +57,15 @@ extern int sysctl_legacy_va_layout; 
extern unsigned long sysctl_user_reserve_kbytes;

extern unsigned long sysctl_admin_reserve_kbytes;



extern int sysctl_overcommit_memory;

extern int sysctl_overcommit_ratio;

extern unsigned long sysctl_overcommit_kbytes;



extern int overcommit_ratio_handler(struct ctl_table *, int, void __user *,

				    size_t *, loff_t *);

extern int overcommit_kbytes_handler(struct ctl_table *, int, void __user *,

				    size_t *, loff_t *);



#define nth_page(page,n) pfn_to_page(page_to_pfn((page)) + (n))



/* to align the pointer to the (next) page boundary */

include/linux/mman.h

+1 −0
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ 


extern int sysctl_overcommit_memory;

extern int sysctl_overcommit_ratio;

extern unsigned long sysctl_overcommit_kbytes;

extern struct percpu_counter vm_committed_as;



#ifdef CONFIG_SMP

kernel/sysctl.c

+8 −3
Original line number Diff line number Diff line
@@ -95,8 +95,6 @@ 
#if defined(CONFIG_SYSCTL)



/* External variables not in a header file. */

extern int sysctl_overcommit_memory;

extern int sysctl_overcommit_ratio;

extern int max_threads;

extern int suid_dumpable;

#ifdef CONFIG_COREDUMP
@@ -1121,7 +1119,14 @@ static struct ctl_table vm_table[] = { 
		.data		= &sysctl_overcommit_ratio,

		.maxlen		= sizeof(sysctl_overcommit_ratio),

		.mode		= 0644,

		.proc_handler	= proc_dointvec,

		.proc_handler	= overcommit_ratio_handler,

	},

	{

		.procname	= "overcommit_kbytes",

		.data		= &sysctl_overcommit_kbytes,

		.maxlen		= sizeof(sysctl_overcommit_kbytes),

		.mode		= 0644,

		.proc_handler	= overcommit_kbytes_handler,

	},

	{

		.procname	= "page-cluster",

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