[PATCH v4 2/2] mm: allow to set overcommit ratio more precisely

From: Jerome Marchand
Date: Fri Oct 18 2013 - 08:57:24 EST

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Changes since v3:
- rebase on 3.12-rc5
Changes since v2:
- updates documentation
Changes since v1:
- use overcommit_ratio_ppm instead of overcommit_kbytes
- keep both variables in sync

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_ratio_ppm sysctl variable that
allow to set overcommit ratio with a part per million precision.
The old overcommit_ratio variable can still be used to set and read
the ratio with a 1% precision. That way, overcommit_ratio interface
isn't broken in any way that I can imagine.

Signed-off-by: Jerome Marchand <jmarchan@xxxxxxxxxx>
---
Documentation/sysctl/vm.txt | 10 +++++
Documentation/vm/overcommit-accounting | 7 ++--
include/linux/mman.h | 6 ++--
include/linux/sysctl.h | 2 +
kernel/sysctl.c | 63 ++++++++++++++++++++++++++++++--
mm/mmap.c | 2 +-
mm/nommu.c | 2 +-
7 files changed, 81 insertions(+), 11 deletions(-)

diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 79a797e..a25943e 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -49,6 +49,7 @@ Currently, these files are in /proc/sys/vm:
- oom_kill_allocating_task
- overcommit_memory
- overcommit_ratio
+- overcommit_ratio_ppm
- page-cluster
- panic_on_oom
- percpu_pagelist_fraction
@@ -599,6 +600,15 @@ overcommit_ratio:
When overcommit_memory is set to 2, the committed address
space is not permitted to exceed swap plus this percentage
of physical RAM. See above.
+If overcommit_ratio_ppm has been set, overcommit_ratio shows a
+rounded value.
+
+==============================================================
+
+overcommit_ratio_ppm:
+
+Same as overcommit_ratio, but allows to set the ratio with a finer
+grain (part per million).

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

diff --git a/Documentation/vm/overcommit-accounting b/Documentation/vm/overcommit-accounting
index 8eaa2fc..15b5ecb 100644
--- a/Documentation/vm/overcommit-accounting
+++ b/Documentation/vm/overcommit-accounting
@@ -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 ratio (default is 50%) of physical RAM.
+ Depending on the ratio 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 percentage is set via `vm.overcommit_ratio' or
+`vm.overcommit_ratio_ppm'.

The current overcommit limit and amount committed are viewable in
/proc/meminfo as CommitLimit and Committed_AS respectively.
diff --git a/include/linux/mman.h b/include/linux/mman.h
index d622d34..24f9c12 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -11,7 +11,7 @@
#include <linux/swap.h>

extern int sysctl_overcommit_memory;
-extern int sysctl_overcommit_ratio;
+extern int sysctl_overcommit_ratio_ppm;
extern struct percpu_counter vm_committed_as;

#ifdef CONFIG_SMP
@@ -96,7 +96,7 @@ calc_vm_flag_bits(unsigned long flags)
*/
static inline unsigned long vm_commit_limit()
{
- return ((totalram_pages - hugetlb_total_pages())
- * sysctl_overcommit_ratio / 100) + total_swap_pages;
+ return ((u64) (totalram_pages - hugetlb_total_pages())
+ * sysctl_overcommit_ratio_ppm / 100000) + total_swap_pages;
}
#endif /* _LINUX_MMAN_H */
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 14a8ff2..2e2389c 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -51,6 +51,8 @@ extern int proc_dointvec_userhz_jiffies(struct ctl_table *, int,
void __user *, size_t *, loff_t *);
extern int proc_dointvec_ms_jiffies(struct ctl_table *, int,
void __user *, size_t *, loff_t *);
+extern int proc_dointvec_percent_ppm(struct ctl_table *, int,
+ void __user *, size_t *, loff_t *);
extern int proc_doulongvec_minmax(struct ctl_table *, int,
void __user *, size_t *, loff_t *);
extern int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int,
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index b2f06f3..ecb22f4 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -96,7 +96,7 @@

/* External variables not in a header file. */
extern int sysctl_overcommit_memory;
-extern int sysctl_overcommit_ratio;
+extern int sysctl_overcommit_ratio_ppm;
extern int max_threads;
extern int suid_dumpable;
#ifdef CONFIG_COREDUMP
@@ -1116,8 +1116,15 @@ static struct ctl_table vm_table[] = {
},
{
.procname = "overcommit_ratio",
- .data = &sysctl_overcommit_ratio,
- .maxlen = sizeof(sysctl_overcommit_ratio),
+ .data = &sysctl_overcommit_ratio_ppm,
+ .maxlen = sizeof(sysctl_overcommit_ratio_ppm),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_percent_ppm,
+ },
+ {
+ .procname = "overcommit_ratio_ppm",
+ .data = &sysctl_overcommit_ratio_ppm,
+ .maxlen = sizeof(sysctl_overcommit_ratio_ppm),
.mode = 0644,
.proc_handler = proc_dointvec,
},
@@ -2433,6 +2440,56 @@ int proc_dointvec_ms_jiffies(struct ctl_table *table, int write,
do_proc_dointvec_ms_jiffies_conv, NULL);
}

+static int do_proc_dointvec_percent_ppm_conv(bool *negp, unsigned long *lvalp,
+ int *valp,
+ int write, void *data)
+{
+ if (write) {
+ unsigned long ppm = (*negp ? -*lvalp : *lvalp) * 10000;
+
+ if (ppm > INT_MAX)
+ return 1;
+ *valp = (int)ppm;
+ } else {
+ int val = *valp;
+ unsigned long lval;
+ if (val < 0) {
+ *negp = true;
+ lval = (unsigned long)-val;
+ } else {
+ *negp = false;
+ lval = (unsigned long)val;
+ }
+ *lvalp = lval / 10000;
+ if (lval % 10000 >= 5000)
+ (*lvalp)++;
+ }
+ return 0;
+}
+
+/**
+ * proc_dointvec_percent_ppm - read a vector of integers as percent and convert it to ppm
+ * @table: the sysctl table
+ * @write: %TRUE if this is a write to the sysctl file
+ * @buffer: the user buffer
+ * @lenp: the size of the user buffer
+ * @ppos: file position
+ * @ppos: the current position in the file
+ *
+ * Reads/writes up to table->maxlen/sizeof(unsigned int) integer
+ * values from/to the user buffer, treated as an ASCII string.
+ * The values read are assumed to be in percents, and are converted
+ * into parts per million.
+ *
+ * Returns 0 on success.
+ */
+int proc_dointvec_percent_ppm(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ return do_proc_dointvec(table, write, buffer, lenp, ppos,
+ do_proc_dointvec_percent_ppm_conv, NULL);
+}
+
static int proc_do_cad_pid(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
diff --git a/mm/mmap.c b/mm/mmap.c
index 7755953..3096d9d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -85,7 +85,7 @@ pgprot_t vm_get_page_prot(unsigned long vm_flags)
EXPORT_SYMBOL(vm_get_page_prot);

int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS; /* heuristic overcommit */
-int sysctl_overcommit_ratio __read_mostly = 50; /* default is 50% */
+int sysctl_overcommit_ratio_ppm __read_mostly = 500000; /* default is 50% */
int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
unsigned long sysctl_user_reserve_kbytes __read_mostly = 1UL << 17; /* 128MB */
unsigned long sysctl_admin_reserve_kbytes __read_mostly = 1UL << 13; /* 8MB */
diff --git a/mm/nommu.c b/mm/nommu.c
index d8a957b..cf10a9b 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -59,7 +59,7 @@ unsigned long max_mapnr;
unsigned long highest_memmap_pfn;
struct percpu_counter vm_committed_as;
int sysctl_overcommit_memory = OVERCOMMIT_GUESS; /* heuristic overcommit */
-int sysctl_overcommit_ratio = 50; /* default is 50% */
+int sysctl_overcommit_ratio_ppm = 500000; /* default is 50% */
int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;
int sysctl_nr_trim_pages = CONFIG_NOMMU_INITIAL_TRIM_EXCESS;
unsigned long sysctl_user_reserve_kbytes __read_mostly = 1UL << 17; /* 128MB */
--
1.7.7.6

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Next message: Mark Brown: "linux-next: manual merge of the net-next tree"
Previous message: Jerome Marchand: "[PATCH v4 1/2] mm: factor commit limit calculation"
In reply to: Jerome Marchand: "[PATCH v4 1/2] mm: factor commit limit calculation"
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