The patch titled
Subject: mm,oom: speed up select_bad_process() loop
has been added to the -mm tree. Its filename is
mmoom-speed-up-select_bad_process-loop.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mmoom-speed-up-select_bad_process-loop.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mmoom-speed-up-select_bad_process-loop.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Subject: mm,oom: speed up select_bad_process() loop
Since commit 3a5dda7a17cf3706 ("oom: prevent unnecessary oom kills or
kernel panics"), select_bad_process() is using for_each_process_thread().
Since oom_unkillable_task() scans all threads in the caller's thread group
and oom_task_origin() scans signal_struct of the caller's thread group, we
don't need to call oom_unkillable_task() and oom_task_origin() on each
thread. Also, since !mm test will be done later at oom_badness(), we
don't need to do !mm test on each thread. Therefore, we only need to do
TIF_MEMDIE test on each thread.
Although the original code was correct it was quite inefficient because
each thread group was scanned num_threads times which can be a lot
especially with processes with many threads. Even though the OOM is
extremely cold path it is always good to be as effective as possible when
we are inside rcu_read_lock() - aka unpreemptible context.
If we track number of TIF_MEMDIE threads inside signal_struct, we don't
need to do TIF_MEMDIE test on each thread. This will allow
select_bad_process() to use for_each_process().
This patch adds a counter to signal_struct for tracking how many
TIF_MEMDIE threads are in a given thread group, and check it at
oom_scan_process_thread() so that select_bad_process() can use
for_each_process() rather than for_each_process_thread().
Link: http://lkml.kernel.org/r/201605182230.IDC73435.MVSOHLFOQFOJtF@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/sched.h | 1 +
mm/oom_kill.c | 14 ++++++--------
2 files changed, 7 insertions(+), 8 deletions(-)
diff -puN include/linux/sched.h~mmoom-speed-up-select_bad_process-loop include/linux/sched.h
--- a/include/linux/sched.h~mmoom-speed-up-select_bad_process-loop
+++ a/include/linux/sched.h
@@ -771,6 +771,7 @@ struct signal_struct {
*/
unsigned long long sum_sched_runtime;
+ atomic_t oom_victims; /* # of TIF_MEDIE threads in this thread group */
/*
* We don't bother to synchronize most readers of this at all,
* because there is no reader checking a limit that actually needs
diff -puN mm/oom_kill.c~mmoom-speed-up-select_bad_process-loop mm/oom_kill.c
--- a/mm/oom_kill.c~mmoom-speed-up-select_bad_process-loop
+++ a/mm/oom_kill.c
@@ -283,12 +283,8 @@ enum oom_scan_t oom_scan_process_thread(
* This task already has access to memory reserves and is being killed.
* Don't allow any other task to have access to the reserves.
*/
- if (test_tsk_thread_flag(task, TIF_MEMDIE)) {
- if (!is_sysrq_oom(oc))
- return OOM_SCAN_ABORT;
- }
- if (!task->mm)
- return OOM_SCAN_CONTINUE;
+ if (!is_sysrq_oom(oc) && atomic_read(&task->signal->oom_victims))
+ return OOM_SCAN_ABORT;
/*
* If task is allocating a lot of memory and has been marked to be
@@ -307,12 +303,12 @@ enum oom_scan_t oom_scan_process_thread(
static struct task_struct *select_bad_process(struct oom_control *oc,
unsigned int *ppoints, unsigned long totalpages)
{
- struct task_struct *g, *p;
+ struct task_struct *p;
struct task_struct *chosen = NULL;
unsigned long chosen_points = 0;
rcu_read_lock();
- for_each_process_thread(g, p) {
+ for_each_process(p) {
unsigned int points;
switch (oom_scan_process_thread(oc, p, totalpages)) {
@@ -673,6 +669,7 @@ void mark_oom_victim(struct task_struct
/* OOM killer might race with memcg OOM */
if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
return;
+ atomic_inc(&tsk->signal->oom_victims);
/*
* Make sure that the task is woken up from uninterruptible sleep
* if it is frozen because OOM killer wouldn't be able to free
@@ -690,6 +687,7 @@ void exit_oom_victim(struct task_struct
{
if (!test_and_clear_tsk_thread_flag(tsk, TIF_MEMDIE))
return;
+ atomic_dec(&tsk->signal->oom_victims);
if (!atomic_dec_return(&oom_victims))
wake_up_all(&oom_victims_wait);
_
Patches currently in -mm which might be from penguin-kernel@xxxxxxxxxxxxxxxxxxx are
mmoom-speed-up-select_bad_process-loop.patch
mmwriteback-dont-use-memory-reserves-for-wb_start_writeback.patch
signal-make-oom_flags-a-bool.patch
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