[PATCH v5 2/2] mm: replace hardcoded 3% with admin_reserve_pages knob
From: Andrew Shewmaker
Date: Wed Mar 06 2013 - 18:54:39 EST
Add an admin_reserve_pages knob to allow admins to change the
hardcoded memory reserve to something other than 3%, which
may be multiple gigabytes on large memory systems.
This affects OVERCOMMIT_GUESS and OVERCOMMIT_NEVER.
admin_reserve_pages is initialized to min(3% free pages, 8MB)
Signed-off-by: Andrew Shewmaker <agshew@xxxxxxxxx>
---
v5:
* Custom sysctl handler was unnecessary
now using proc_doulongvec_minmax()
v4:
* Rebased onto v3.8-mmotm-2013-03-01-15-50
* No longer assumes 4kb pages
* Code duplicated for nommu
v3:
* New patch summary because it wasn't unique
New is "mm: replace hardcoded 3% with admin_reserve_pages knob"
Old was "mm: tuning hardcoded reserve memory"
* Limits growth to min(3% process size, k)
as Alan Cox suggested. I chose k=2000 pages to allow
recovery with sshd or login, bash, and top or kill
v2:
* Based onto v3.8-mmotm-2013-02-19-17-20
* Simple tunable added that initialized to 1000 pages
v1:
* I asked for comments concerning this idea when submitting v1
of the patch to remove the user reserve
---
Documentation/sysctl/vm.txt | 15 +++++++++++++++
kernel/sysctl.c | 8 ++++++++
mm/mmap.c | 30 ++++++++++++++++++++++++++----
mm/nommu.c | 30 ++++++++++++++++++++++++++----
4 files changed, 75 insertions(+), 8 deletions(-)
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 40c2a49..60b9aba 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_pages
- block_dump
- compact_memory
- dirty_background_bytes
@@ -59,6 +60,20 @@ Currently, these files are in /proc/sys/vm:
==============================================================
+admin_reserve_pages
+
+The number of free pages in the system that should be reserved for users
+with the capability cap_sys_admin. The default value is the smaller of 3%
+of free pages or 8MB (2048 pages). That should provide enough for the
+admin to log in and kill a process if necessary.
+
+Systems running with overcommit disabled should consider increasing this
+to account for the full Virtual Memory Size of programs used to recover.
+
+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
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index dbb7b93..9c5aae6 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -98,6 +98,7 @@
extern int sysctl_overcommit_memory;
extern int sysctl_overcommit_ratio;
extern unsigned long sysctl_user_reserve_pages;
+extern unsigned long sysctl_admin_reserve_pages;
extern int max_threads;
extern int suid_dumpable;
#ifdef CONFIG_COREDUMP
@@ -1438,6 +1439,13 @@ static struct ctl_table vm_table[] = {
.mode = 0644,
.proc_handler = proc_doulongvec_minmax,
},
+ {
+ .procname = "admin_reserve_pages",
+ .data = &sysctl_admin_reserve_pages,
+ .maxlen = sizeof(sysctl_admin_reserve_pages),
+ .mode = 0644,
+ .proc_handler = proc_doulongvec_minmax,
+ },
{ }
};
diff --git a/mm/mmap.c b/mm/mmap.c
index aeaf83f..78743ab 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -86,6 +86,7 @@ int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS; /* heuristic ove
int sysctl_overcommit_ratio __read_mostly = 50; /* default is 50% */
int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
unsigned long sysctl_user_reserve_pages __read_mostly = 1UL << (27 - PAGE_SHIFT); /* 128MB */
+unsigned long sysctl_admin_reserve_pages __read_mostly = 1UL << (23 - PAGE_SHIFT); /* 8MB */
/*
* Make sure vm_committed_as in one cacheline and not cacheline shared with
* other variables. It can be updated by several CPUs frequently.
@@ -165,10 +166,10 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
free -= totalreserve_pages;
/*
- * Leave the last 3% for root
+ * Reserve some for root
*/
if (!cap_sys_admin)
- free -= free / 32;
+ free -= sysctl_admin_reserve_pages;
if (free > pages)
return 0;
@@ -179,10 +180,10 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
allowed = (totalram_pages - hugetlb_total_pages())
* sysctl_overcommit_ratio / 100;
/*
- * Leave the last 3% for root
+ * Reserve some for root
*/
if (!cap_sys_admin)
- allowed -= allowed / 32;
+ allowed -= sysctl_admin_reserve_pages;
allowed += total_swap_pages;
/*
@@ -3090,3 +3091,24 @@ int __meminit init_user_reserve(void)
return 0;
}
module_init(init_user_reserve)
+
+/*
+ * Initialise sysctl_admin_reserve_pages.
+ *
+ * The purpose of sysctl_admin_reserve_pages is to allow the sys admin
+ * to log in and kill a memory hogging process.
+ *
+ * Systems with more than 256MB will reserve 8MB, enough to recover
+ * with sshd, bash, and top. Smaller systems will only reserve 3% of
+ * free pages by default.
+ */
+int __meminit init_admin_reserve(void)
+{
+ unsigned long free;
+
+ free = global_page_state(NR_FREE_PAGES);
+
+ sysctl_admin_reserve_pages = min(free / 32, 1UL << (23 - PAGE_SHIFT));
+ return 0;
+}
+module_init(init_admin_reserve)
diff --git a/mm/nommu.c b/mm/nommu.c
index 0137ab2..70282a1 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -65,6 +65,7 @@ int sysctl_overcommit_ratio = 50; /* 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_pages __read_mostly = 1UL << (27 - PAGE_SHIFT); /* 128MB */
+unsigned long sysctl_admin_reserve_pages __read_mostly = 1UL << (23 - PAGE_SHIFT); /* 8MB */
int heap_stack_gap = 0;
atomic_long_t mmap_pages_allocated;
@@ -1927,10 +1928,10 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
free -= totalreserve_pages;
/*
- * Leave the last 3% for root
+ * Reserve some for root
*/
if (!cap_sys_admin)
- free -= free / 32;
+ free -= sysctl_admin_reserve_pages;
if (free > pages)
return 0;
@@ -1940,10 +1941,10 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
allowed = totalram_pages * sysctl_overcommit_ratio / 100;
/*
- * Leave the last 3% for root
+ * Reserve some 3% for root
*/
if (!cap_sys_admin)
- allowed -= allowed / 32;
+ allowed -= sysctl_admin_reserve_pages;
allowed += total_swap_pages;
/* Don't let a single process grow too big:
@@ -2133,3 +2134,24 @@ int __meminit init_user_reserve(void)
return 0;
}
module_init(init_user_reserve)
+
+/*
+ * Initialise sysctl_admin_reserve_pages.
+ *
+ * The purpose of sysctl_admin_reserve_pages is to allow the sys admin
+ * to log in and kill a memory hogging process.
+ *
+ * Systems with more than 256MB will reserve 8MB, enough to recover
+ * with sshd, bash, and top. Smaller systems will only reserve 3% of
+ * free pages by default.
+ */
+int __meminit init_admin_reserve(void)
+{
+ unsigned long free;
+
+ free = global_page_state(NR_FREE_PAGES);
+
+ sysctl_admin_reserve_pages = min(free / 32, 1UL << (23 - PAGE_SHIFT));
+ return 0;
+}
+module_init(init_admin_reserve)
--
1.8.0.1
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