The patch titled
mm: avoid false sharing of mm_counter
has been added to the -mm tree. Its filename is
mm-avoid-false-sharing-of-mm_counter.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: mm: avoid false sharing of mm_counter
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Considering the nature of per mm stats, it's the shared object among
threads and can be a cache-miss point in the page fault path.
This patch adds per-thread cache for mm_counter. RSS value will be
counted into a struct in task_struct and synchronized with mm's one at
events.
Now, in this patch, the event is the number of calls to handle_mm_fault.
Per-thread value is added to mm at each 64 calls.
rough estimation with small benchmark on parallel thread (2threads) shows
[before]
4.5 cache-miss/faults
[after]
4.0 cache-miss/faults
Anyway, the most contended object is mmap_sem if the number of threads grows.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
Cc: Lee Schermerhorn <lee.schermerhorn@xxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/filesystems/proc.txt | 6 +
fs/exec.c | 1
include/linux/mm.h | 8 --
include/linux/mm_types.h | 6 +
include/linux/sched.h | 4 -
kernel/exit.c | 3
mm/memory.c | 94 ++++++++++++++++++++++++---
7 files changed, 107 insertions(+), 15 deletions(-)
diff -puN Documentation/filesystems/proc.txt~mm-avoid-false-sharing-of-mm_counter Documentation/filesystems/proc.txt
--- a/Documentation/filesystems/proc.txt~mm-avoid-false-sharing-of-mm_counter
+++ a/Documentation/filesystems/proc.txt
@@ -189,6 +189,12 @@ memory usage. Its seven fields are expla
contains details information about the process itself. Its fields are
explained in Table 1-4.
+(for SMP CONFIG users)
+For making accounting scalable, RSS related information are handled in
+asynchronous manner and the vaule may not be very precise. To see a precise
+snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
+It's slow but very precise.
+
Table 1-2: Contents of the statm files (as of 2.6.30-rc7)
..............................................................................
Field Content
diff -puN fs/exec.c~mm-avoid-false-sharing-of-mm_counter fs/exec.c
--- a/fs/exec.c~mm-avoid-false-sharing-of-mm_counter
+++ a/fs/exec.c
@@ -702,6 +702,7 @@ static int exec_mmap(struct mm_struct *m
/* Notify parent that we're no longer interested in the old VM */
tsk = current;
old_mm = current->mm;
+ sync_mm_rss(tsk, old_mm);
mm_release(tsk, old_mm);
if (old_mm) {
diff -puN include/linux/mm.h~mm-avoid-false-sharing-of-mm_counter include/linux/mm.h
--- a/include/linux/mm.h~mm-avoid-false-sharing-of-mm_counter
+++ a/include/linux/mm.h
@@ -870,7 +870,7 @@ int __get_user_pages_fast(unsigned long
/*
* per-process(per-mm_struct) statistics.
*/
-#if USE_SPLIT_PTLOCKS
+#if defined(SPLIT_RSS_COUNTING)
/*
* The mm counters are not protected by its page_table_lock,
* so must be incremented atomically.
@@ -880,10 +880,7 @@ static inline void set_mm_counter(struct
atomic_long_set(&mm->rss_stat.count[member], value);
}
-static inline unsigned long get_mm_counter(struct mm_struct *mm, int member)
-{
- return (unsigned long)atomic_long_read(&mm->rss_stat.count[member]);
-}
+unsigned long get_mm_counter(struct mm_struct *mm, int member);
static inline void add_mm_counter(struct mm_struct *mm, int member, long value)
{
@@ -971,6 +968,7 @@ static inline void setmax_mm_hiwater_rss
*maxrss = hiwater_rss;
}
+void sync_mm_rss(struct task_struct *task, struct mm_struct *mm);
/*
* A callback you can register to apply pressure to ageable caches.
diff -puN include/linux/mm_types.h~mm-avoid-false-sharing-of-mm_counter include/linux/mm_types.h
--- a/include/linux/mm_types.h~mm-avoid-false-sharing-of-mm_counter
+++ a/include/linux/mm_types.h
@@ -200,9 +200,15 @@ enum {
};
#if USE_SPLIT_PTLOCKS
+#define SPLIT_RSS_COUNTING
struct mm_rss_stat {
atomic_long_t count[NR_MM_COUNTERS];
};
+/* per-thread cached information, */
+struct task_rss_stat {
+ int events; /* for synchronization threshold */
+ int count[NR_MM_COUNTERS];
+};
#else /* !USE_SPLIT_PTLOCKS */
struct mm_rss_stat {
unsigned long count[NR_MM_COUNTERS];
diff -puN include/linux/sched.h~mm-avoid-false-sharing-of-mm_counter include/linux/sched.h
--- a/include/linux/sched.h~mm-avoid-false-sharing-of-mm_counter
+++ a/include/linux/sched.h
@@ -1223,7 +1223,9 @@ struct task_struct {
struct plist_node pushable_tasks;
struct mm_struct *mm, *active_mm;
-
+#if defined(SPLIT_RSS_COUNTING)
+ struct task_rss_stat rss_stat;
+#endif
/* task state */
int exit_state;
int exit_code, exit_signal;
diff -puN kernel/exit.c~mm-avoid-false-sharing-of-mm_counter kernel/exit.c
--- a/kernel/exit.c~mm-avoid-false-sharing-of-mm_counter
+++ a/kernel/exit.c
@@ -944,7 +944,8 @@ NORET_TYPE void do_exit(long code)
preempt_count());
acct_update_integrals(tsk);
-
+ /* sync mm's RSS info before statistics gathering */
+ sync_mm_rss(tsk, tsk->mm);
group_dead = atomic_dec_and_test(&tsk->signal->live);
if (group_dead) {
hrtimer_cancel(&tsk->signal->real_timer);
diff -puN mm/memory.c~mm-avoid-false-sharing-of-mm_counter mm/memory.c
--- a/mm/memory.c~mm-avoid-false-sharing-of-mm_counter
+++ a/mm/memory.c
@@ -122,6 +122,79 @@ static int __init init_zero_pfn(void)
core_initcall(init_zero_pfn);
+#if defined(SPLIT_RSS_COUNTING)
+
+void __sync_task_rss_stat(struct task_struct *task, struct mm_struct *mm)
+{
+ int i;
+
+ for (i = 0; i < NR_MM_COUNTERS; i++) {
+ if (task->rss_stat.count[i]) {
+ add_mm_counter(mm, i, task->rss_stat.count[i]);
+ task->rss_stat.count[i] = 0;
+ }
+ }
+ task->rss_stat.events = 0;
+}
+
+static void add_mm_counter_fast(struct mm_struct *mm, int member, int val)
+{
+ struct task_struct *task = current;
+
+ if (likely(task->mm == mm))
+ task->rss_stat.count[member] += val;
+ else
+ add_mm_counter(mm, member, val);
+}
+#define inc_mm_counter_fast(mm, member) add_mm_counter_fast(mm, member,1)
+#define dec_mm_counter_fast(mm, member) add_mm_counter_fast(mm, member,-1)
+
+/* sync counter once per 64 page faults */
+#define TASK_RSS_EVENTS_THRESH (64)
+static void check_sync_rss_stat(struct task_struct *task)
+{
+ if (unlikely(task != current))
+ return;
+ if (unlikely(task->rss_stat.events++ > TASK_RSS_EVENTS_THRESH))
+ __sync_task_rss_stat(task, task->mm);
+}
+
+unsigned long get_mm_counter(struct mm_struct *mm, int member)
+{
+ long val = 0;
+
+ /*
+ * Don't use task->mm here...for avoiding to use task_get_mm()..
+ * The caller must guarantee task->mm is not invalid.
+ */
+ val = atomic_long_read(&mm->rss_stat.count[member]);
+ /*
+ * counter is updated in asynchronous manner and may go to minus.
+ * But it's never be expected number for users.
+ */
+ if (val < 0)
+ return 0;
+ return (unsigned long)val;
+}
+
+void sync_mm_rss(struct task_struct *task, struct mm_struct *mm)
+{
+ __sync_task_rss_stat(task, mm);
+}
+#else
+
+#define inc_mm_counter_fast(mm, member) inc_mm_counter(mm, member)
+#define dec_mm_counter_fast(mm, member) dec_mm_counter(mm, member)
+
+static void check_sync_rss_stat(struct task_struct *task)
+{
+}
+
+void sync_mm_rss(struct task_struct *task, struct mm_struct *mm)
+{
+}
+#endif
+
/*
* If a p?d_bad entry is found while walking page tables, report
* the error, before resetting entry to p?d_none. Usually (but
@@ -386,6 +459,8 @@ static inline void add_mm_rss_vec(struct
{
int i;
+ if (current->mm == mm)
+ sync_mm_rss(current, mm);
for (i = 0; i < NR_MM_COUNTERS; i++)
if (rss[i])
add_mm_counter(mm, i, rss[i]);
@@ -1539,7 +1614,7 @@ static int insert_page(struct vm_area_st
/* Ok, finally just insert the thing.. */
get_page(page);
- inc_mm_counter(mm, MM_FILEPAGES);
+ inc_mm_counter_fast(mm, MM_FILEPAGES);
page_add_file_rmap(page);
set_pte_at(mm, addr, pte, mk_pte(page, prot));
@@ -2175,11 +2250,11 @@ gotten:
if (likely(pte_same(*page_table, orig_pte))) {
if (old_page) {
if (!PageAnon(old_page)) {
- dec_mm_counter(mm, MM_FILEPAGES);
- inc_mm_counter(mm, MM_ANONPAGES);
+ dec_mm_counter_fast(mm, MM_FILEPAGES);
+ inc_mm_counter_fast(mm, MM_ANONPAGES);
}
} else
- inc_mm_counter(mm, MM_ANONPAGES);
+ inc_mm_counter_fast(mm, MM_ANONPAGES);
flush_cache_page(vma, address, pte_pfn(orig_pte));
entry = mk_pte(new_page, vma->vm_page_prot);
entry = maybe_mkwrite(pte_mkdirty(entry), vma);
@@ -2616,7 +2691,7 @@ static int do_swap_page(struct mm_struct
* discarded at swap_free().
*/
- inc_mm_counter(mm, MM_ANONPAGES);
+ inc_mm_counter_fast(mm, MM_ANONPAGES);
pte = mk_pte(page, vma->vm_page_prot);
if ((flags & FAULT_FLAG_WRITE) && reuse_swap_page(page)) {
pte = maybe_mkwrite(pte_mkdirty(pte), vma);
@@ -2700,7 +2775,7 @@ static int do_anonymous_page(struct mm_s
if (!pte_none(*page_table))
goto release;
- inc_mm_counter(mm, MM_ANONPAGES);
+ inc_mm_counter_fast(mm, MM_ANONPAGES);
page_add_new_anon_rmap(page, vma, address);
setpte:
set_pte_at(mm, address, page_table, entry);
@@ -2854,10 +2929,10 @@ static int __do_fault(struct mm_struct *
if (flags & FAULT_FLAG_WRITE)
entry = maybe_mkwrite(pte_mkdirty(entry), vma);
if (anon) {
- inc_mm_counter(mm, MM_ANONPAGES);
+ inc_mm_counter_fast(mm, MM_ANONPAGES);
page_add_new_anon_rmap(page, vma, address);
} else {
- inc_mm_counter(mm, MM_FILEPAGES);
+ inc_mm_counter_fast(mm, MM_FILEPAGES);
page_add_file_rmap(page);
if (flags & FAULT_FLAG_WRITE) {
dirty_page = page;
@@ -3035,6 +3110,9 @@ int handle_mm_fault(struct mm_struct *mm
count_vm_event(PGFAULT);
+ /* do counter updates before entering really critical section. */
+ check_sync_rss_stat(current);
+
if (unlikely(is_vm_hugetlb_page(vma)))
return hugetlb_fault(mm, vma, address, flags);
_
Patches currently in -mm which might be from kamezawa.hiroyu@xxxxxxxxxxxxxx are
mm-add-notifier-in-pageblock-isolation-for-balloon-drivers.patch
powerpc-make-the-cmm-memory-hotplug-aware.patch
mm-clean-up-mm_counter.patch
mm-avoid-false-sharing-of-mm_counter.patch
mm-count-swap-usage.patch
mm-add-lowmem-detection-logic.patch
mm-count-lowmem-rss.patch
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