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 | 3 +--
include/linux/oom.h | 3 ++-
mm/oom_kill.c | 57 ++++++++++++++++++++++++++++++++---------------------
mm/page_alloc.c | 2 +-
4 files changed, 39 insertions(+), 26 deletions(-)
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 3a42b7187b8e..06a95a8ed701 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -356,8 +356,7 @@ static struct sysrq_key_op sysrq_term_op = {
static void moom_callback(struct work_struct *ignored)
{
mutex_lock(&oom_lock);
- if (!out_of_memory(node_zonelist(first_memory_node, GFP_KERNEL),
- GFP_KERNEL, 0, NULL, true))
+ 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 7deecb7bca5e..061e0ffd3493 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -70,8 +70,9 @@ extern enum oom_scan_t oom_scan_process_thread(struct task_struct *task,
unsigned long totalpages, const nodemask_t *nodemask,
bool force_kill);
+extern bool force_out_of_memory(void);
extern bool out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
- int order, nodemask_t *mask, bool force_kill);
+ int order, nodemask_t *mask);
extern void exit_oom_victim(void);
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 0c312eaac834..050936f35944 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -635,12 +635,38 @@ int unregister_oom_notifier(struct notifier_block *nb)
EXPORT_SYMBOL_GPL(unregister_oom_notifier);
/**
- * __out_of_memory - kill the "best" process when we run out of memory
+ * force_out_of_memory - forces OOM killer
+ *
+ * External trigger for the OOM killer. The system doesn't have to be under
+ * OOM condition (e.g. sysrq+f).
+ */
+bool force_out_of_memory(void)
+{
+ struct zonelist *zonelist = node_zonelist(first_memory_node, GFP_KERNEL);
+ struct task_struct *p;
+ unsigned long totalpages;
+ unsigned int points;
+
+ if (oom_killer_disabled)
+ return false;
+
+ constrained_alloc(zonelist, GFP_KERNEL, NULL, &totalpages);
+ p = select_bad_process(&points, totalpages, NULL, true);
+ if (p != (void *)-1UL)
+ oom_kill_process(p, GFP_KERNEL, 0, points, totalpages, NULL,
+ NULL, "Forced out of memory killer");
+ else
+ pr_warn("Forced out of memory. No killable task found...\n");
+
+ return true;
+}
+
+/**
+ * out_of_memory - kill the "best" process when we run out of memory
* @zonelist: zonelist pointer
* @gfp_mask: memory allocation flags
* @order: amount of memory being requested as a power of 2
* @nodemask: nodemask passed to page allocator
- * @force_kill: true if a task must be killed, even if others are exiting
*
* If we run out of memory, we have the choice between either
* killing a random task (bad), letting the system crash (worse)
@@ -648,7 +674,7 @@ EXPORT_SYMBOL_GPL(unregister_oom_notifier);
* don't have to be perfect here, we just have to be good.
*/
bool out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
- int order, nodemask_t *nodemask, bool force_kill)
+ int order, nodemask_t *nodemask)
{
const nodemask_t *mpol_mask;
struct task_struct *p;
@@ -687,14 +713,8 @@ bool out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
constraint = constrained_alloc(zonelist, gfp_mask, nodemask,
&totalpages);
mpol_mask = (constraint == CONSTRAINT_MEMORY_POLICY) ? nodemask : NULL;
- /* Ignore panic_on_oom when the OOM killer is sysrq triggered */
- if (!force_kill)
- check_panic_on_oom(constraint, gfp_mask, order, mpol_mask, NULL);
+ check_panic_on_oom(constraint, gfp_mask, order, mpol_mask, 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, nodemask) &&
current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
@@ -705,18 +725,11 @@ bool out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
goto out;
}
- p = select_bad_process(&points, totalpages, mpol_mask, force_kill);
- /*
- * Found nothing?!?! Either we hang forever, or we panic.
- * Do not panic when the OOM killer is sysrq triggered.
- */
+ p = select_bad_process(&points, totalpages, mpol_mask, false);
+ /* Found nothing?!?! Either we hang forever, or we panic. */
if (!p) {
- if (!force_kill) {
- dump_header(NULL, gfp_mask, order, NULL, mpol_mask);
- panic("Out of memory and no killable processes...\n");
- } else {
- pr_info("Forced out of memory. No killable task found...\n");
- }
+ dump_header(NULL, gfp_mask, order, NULL, mpol_mask);
+ panic("Out of memory and no killable processes...\n");
}
if (p != (void *)-1UL) {
oom_kill_process(p, gfp_mask, order, points, totalpages, NULL,
@@ -747,7 +760,7 @@ void pagefault_out_of_memory(void)
if (!mutex_trylock(&oom_lock))
return;
- if (!out_of_memory(NULL, 0, 0, NULL, false)) {
+ if (!out_of_memory(NULL, 0, 0, NULL)) {
/*
* There shouldn't be any user tasks runnable while the
* OOM killer is disabled, so the current task has to
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1f9ffbb087cb..014806d13138 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2731,7 +2731,7 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
goto out;
}
/* Exhausted what can be done so it's blamo time */
- if (out_of_memory(ac->zonelist, gfp_mask, order, ac->nodemask, false)
+ if (out_of_memory(ac->zonelist, gfp_mask, order, ac->nodemask)
|| WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL))
*did_some_progress = 1;
out:
--
2.1.4
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