From: Michal Hocko <mhocko@xxxxxxx>
The forced OOM killing is currently wired into out_of_memory() call
even though their objective is different which makes the code ugly
and harder to follow. Generic out_of_memory path has to deal with
configuration settings and heuristics which are completely irrelevant
to the forced OOM killer (e.g. sysctl_oom_kill_allocating_task or
OOM killer prevention for already dying tasks). All of them are
either relying on explicit force_kill check or indirectly by checking
current->mm which is always NULL for sysrq+f. This is not nice, hard
to follow and error prone.
Let's pull forced OOM killer code out into a separate function
(force_out_of_memory) which is really trivial now.
As a bonus we can clearly state that this is a forced OOM killer
in the OOM message which is helpful to distinguish it from the
regular OOM killer.
Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
---
drivers/tty/sysrq.c | 9 +--------
include/linux/oom.h | 1 +
mm/oom_kill.c | 57 ++++++++++++++++++++++++++++++++++++-----------------
3 files changed, 41 insertions(+), 26 deletions(-)
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 865b837a9aee..6a3def693ded 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -356,15 +356,8 @@ static struct sysrq_key_op sysrq_term_op = {
static void moom_callback(struct work_struct *ignored)
{
- const gfp_t gfp_mask = GFP_KERNEL;
- struct oom_context oc = {
- .zonelist = node_zonelist(first_memory_node, gfp_mask),
- .gfp_mask = gfp_mask,
- .force_kill = true,
- };
-
mutex_lock(&oom_lock);
- if (!out_of_memory(&oc))
+ if (!force_out_of_memory())
pr_info("OOM request ignored because killer is disabled\n");
mutex_unlock(&oom_lock);
}
diff --git a/include/linux/oom.h b/include/linux/oom.h
index 094407cb2d2e..6af2d12d6134 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -77,6 +77,7 @@ extern enum oom_scan_t oom_scan_process_thread(struct oom_context *oc,
struct task_struct *task, unsigned long totalpages);
extern bool out_of_memory(struct oom_context *oc);
+extern bool force_out_of_memory(void);
extern void exit_oom_victim(void);
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 01aa4cb86857..6a0b09296236 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -627,6 +627,38 @@ int unregister_oom_notifier(struct notifier_block *nb)
EXPORT_SYMBOL_GPL(unregister_oom_notifier);
/**
+ * force_out_of_memory - forces OOM killer to kill a process
+ *
+ * Explicitly trigger the OOM killer. The system doesn't have to be under
+ * OOM condition (e.g. sysrq+f).
+ */
+bool force_out_of_memory(void)
+{
+ struct task_struct *p;
+ unsigned long totalpages;
+ unsigned int points;
+ const gfp_t gfp_mask = GFP_KERNEL;
+ struct oom_context oc = {
+ .zonelist = node_zonelist(first_memory_node, gfp_mask),
+ .gfp_mask = gfp_mask,
+ .force_kill = true,
+ };
+
+ if (oom_killer_disabled)
+ return false;
+
+ constrained_alloc(&oc, &totalpages);
+ p = select_bad_process(&oc, &points, totalpages);
+ if (p != (void *)-1UL)
+ oom_kill_process(&oc, p, points, totalpages, NULL,
+ "Forced out of memory killer");
+ else
+ pr_warn("Sysrq triggered out of memory. No killable task found...\n");
+
+ return true;
+}
+
+/**
* out_of_memory - kill the "best" process when we run out of memory
* @oc: pointer to struct oom_context
*
@@ -647,12 +679,10 @@ bool out_of_memory(struct oom_context *oc)
if (oom_killer_disabled)
return false;
- if (!oc->force_kill) {
- blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
- if (freed > 0)
- /* Got some memory back in the last second. */
- goto out;
- }
+ blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
+ if (freed > 0)
+ /* Got some memory back in the last second. */
+ goto out;
/*
* If current has a pending SIGKILL or is exiting, then automatically
@@ -675,13 +705,8 @@ bool out_of_memory(struct oom_context *oc)
constraint = constrained_alloc(oc, &totalpages);
if (constraint != CONSTRAINT_MEMORY_POLICY)
oc->nodemask = NULL;
- if (!oc->force_kill)
- check_panic_on_oom(oc, constraint, NULL);
+ check_panic_on_oom(oc, constraint, NULL);
- /*
- * not affecting force_kill because sysrq triggered OOM killer runs from
- * the workqueue context so current->mm will be NULL
- */
if (sysctl_oom_kill_allocating_task && current->mm &&
!oom_unkillable_task(current, NULL, oc->nodemask) &&
current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
@@ -694,12 +719,8 @@ bool out_of_memory(struct oom_context *oc)
p = select_bad_process(oc, &points, totalpages);
/* Found nothing?!?! Either we hang forever, or we panic. */
if (!p) {
- if (!oc->force_kill) {
- dump_header(oc, NULL, NULL);
- panic("Out of memory and no killable processes...\n");
- } else {
- pr_info("Sysrq triggered out of memory. No killable task found...\n");
- }
+ dump_header(oc, NULL, NULL);
+ panic("Out of memory and no killable processes...\n");
}
if (p != (void *)-1UL) {
oom_kill_process(oc, p, points, totalpages, NULL,
--
2.1.4
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