The patch titled
Subject: mm, oom: reduce dependency on tasklist_lock
has been added to the -mm tree. Its filename is
mm-oom-reduce-dependency-on-tasklist_lock.patch
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------------------------------------------------------
From: David Rientjes <rientjes@xxxxxxxxxx>
Subject: mm, oom: reduce dependency on tasklist_lock
Since exiting tasks require write_lock_irq(&tasklist_lock) several times,
try to reduce the amount of time the readside is held for oom kills. This
makes the interface with the memcg oom handler more consistent since it
now never needs to take tasklist_lock unnecessarily.
The only time the oom killer now takes tasklist_lock is when iterating the
children of the selected task, everything else is protected by
rcu_read_lock().
This requires that a reference to the selected process, p, is grabbed
before calling oom_kill_process(). It may release it and grab a reference
on another one of p's threads if !p->mm, but it also guarantees that it
will release the reference before returning.
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 2 --
mm/oom_kill.c | 40 +++++++++++++++++++++++++++++-----------
2 files changed, 29 insertions(+), 13 deletions(-)
diff -puN mm/memcontrol.c~mm-oom-reduce-dependency-on-tasklist_lock mm/memcontrol.c
--- a/mm/memcontrol.c~mm-oom-reduce-dependency-on-tasklist_lock
+++ a/mm/memcontrol.c
@@ -1521,10 +1521,8 @@ void __mem_cgroup_out_of_memory(struct m
if (!chosen)
return;
points = chosen_points * 1000 / totalpages;
- read_lock(&tasklist_lock);
oom_kill_process(chosen, gfp_mask, order, points, totalpages, memcg,
NULL, "Memory cgroup out of memory");
- read_unlock(&tasklist_lock);
put_task_struct(chosen);
}
diff -puN mm/oom_kill.c~mm-oom-reduce-dependency-on-tasklist_lock mm/oom_kill.c
--- a/mm/oom_kill.c~mm-oom-reduce-dependency-on-tasklist_lock
+++ a/mm/oom_kill.c
@@ -336,7 +336,7 @@ enum oom_scan_t oom_scan_process_thread(
/*
* Simple selection loop. We chose the process with the highest
- * number of 'points'. We expect the caller will lock the tasklist.
+ * number of 'points'.
*
* (not docbooked, we don't want this one cluttering up the manual)
*/
@@ -348,6 +348,7 @@ static struct task_struct *select_bad_pr
struct task_struct *chosen = NULL;
unsigned long chosen_points = 0;
+ rcu_read_lock();
do_each_thread(g, p) {
unsigned int points;
@@ -370,6 +371,9 @@ static struct task_struct *select_bad_pr
chosen_points = points;
}
} while_each_thread(g, p);
+ if (chosen)
+ get_task_struct(chosen);
+ rcu_read_unlock();
*ppoints = chosen_points * 1000 / totalpages;
return chosen;
@@ -385,8 +389,6 @@ static struct task_struct *select_bad_pr
* are not shown.
* State information includes task's pid, uid, tgid, vm size, rss, nr_ptes,
* swapents, oom_score_adj value, and name.
- *
- * Call with tasklist_lock read-locked.
*/
static void dump_tasks(const struct mem_cgroup *memcg, const nodemask_t *nodemask)
{
@@ -394,6 +396,7 @@ static void dump_tasks(const struct mem_
struct task_struct *task;
pr_info("[ pid ] uid tgid total_vm rss nr_ptes swapents oom_score_adj name\n");
+ rcu_read_lock();
for_each_process(p) {
if (oom_unkillable_task(p, memcg, nodemask))
continue;
@@ -416,6 +419,7 @@ static void dump_tasks(const struct mem_
task->signal->oom_score_adj, task->comm);
task_unlock(task);
}
+ rcu_read_unlock();
}
static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
@@ -436,6 +440,10 @@ static void dump_header(struct task_stru
}
#define K(x) ((x) << (PAGE_SHIFT-10))
+/*
+ * Must be called while holding a reference to p, which will be released upon
+ * returning.
+ */
void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
unsigned int points, unsigned long totalpages,
struct mem_cgroup *memcg, nodemask_t *nodemask,
@@ -455,6 +463,7 @@ void oom_kill_process(struct task_struct
*/
if (p->flags & PF_EXITING) {
set_tsk_thread_flag(p, TIF_MEMDIE);
+ put_task_struct(p);
return;
}
@@ -472,6 +481,7 @@ void oom_kill_process(struct task_struct
* parent. This attempts to lose the minimal amount of work done while
* still freeing memory.
*/
+ read_lock(&tasklist_lock);
do {
list_for_each_entry(child, &t->children, sibling) {
unsigned int child_points;
@@ -484,15 +494,26 @@ void oom_kill_process(struct task_struct
child_points = oom_badness(child, memcg, nodemask,
totalpages);
if (child_points > victim_points) {
+ put_task_struct(victim);
victim = child;
victim_points = child_points;
+ get_task_struct(victim);
}
}
} while_each_thread(p, t);
+ read_unlock(&tasklist_lock);
- victim = find_lock_task_mm(victim);
- if (!victim)
+ rcu_read_lock();
+ p = find_lock_task_mm(victim);
+ if (!p) {
+ rcu_read_unlock();
+ put_task_struct(victim);
return;
+ } else if (victim != p) {
+ get_task_struct(p);
+ put_task_struct(victim);
+ victim = p;
+ }
/* mm cannot safely be dereferenced after task_unlock(victim) */
mm = victim->mm;
@@ -523,9 +544,11 @@ void oom_kill_process(struct task_struct
task_unlock(p);
do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
}
+ rcu_read_unlock();
set_tsk_thread_flag(victim, TIF_MEMDIE);
do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
+ put_task_struct(victim);
}
#undef K
@@ -546,9 +569,7 @@ static void check_panic_on_oom(enum oom_
if (constraint != CONSTRAINT_NONE)
return;
}
- read_lock(&tasklist_lock);
dump_header(NULL, gfp_mask, order, NULL, nodemask);
- read_unlock(&tasklist_lock);
panic("Out of memory: %s panic_on_oom is enabled\n",
sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
}
@@ -721,10 +742,10 @@ void out_of_memory(struct zonelist *zone
mpol_mask = (constraint == CONSTRAINT_MEMORY_POLICY) ? nodemask : NULL;
check_panic_on_oom(constraint, gfp_mask, order, mpol_mask);
- read_lock(&tasklist_lock);
if (sysctl_oom_kill_allocating_task && current->mm &&
!oom_unkillable_task(current, NULL, nodemask) &&
current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
+ get_task_struct(current);
oom_kill_process(current, gfp_mask, order, 0, totalpages, NULL,
nodemask,
"Out of memory (oom_kill_allocating_task)");
@@ -735,7 +756,6 @@ void out_of_memory(struct zonelist *zone
/* Found nothing?!?! Either we hang forever, or we panic. */
if (!p) {
dump_header(NULL, gfp_mask, order, NULL, mpol_mask);
- read_unlock(&tasklist_lock);
panic("Out of memory and no killable processes...\n");
}
if (PTR_ERR(p) != -1UL) {
@@ -744,8 +764,6 @@ void out_of_memory(struct zonelist *zone
killed = 1;
}
out:
- read_unlock(&tasklist_lock);
-
/*
* Give the killed threads a good chance of exiting before trying to
* allocate memory again.
_
Subject: Subject: mm, oom: reduce dependency on tasklist_lock
Patches currently in -mm which might be from rientjes@xxxxxxxxxx are
linux-next.patch
memory-hotplug-fix-invalid-memory-access-caused-by-stale-kswapd-pointer.patch
memory-hotplug-fix-invalid-memory-access-caused-by-stale-kswapd-pointer-fix.patch
mm-thp-abort-compaction-if-migration-page-cannot-be-charged-to-memcg.patch
mm-memory_hotplugc-release-memory-resources-if-hotadd_new_pgdat-fails.patch
slab-do-not-call-compound_head-in-page_get_cache.patch
mm-buddy-cleanup-on-should_fail_alloc_page.patch
hugetlb-rename-max_hstate-to-hugetlb_max_hstate.patch
hugetlb-dont-use-err_ptr-with-vm_fault-values.patch
hugetlb-add-an-inline-helper-for-finding-hstate-index.patch
hugetlb-use-mmu_gather-instead-of-a-temporary-linked-list-for-accumulating-pages.patch
hugetlb-avoid-taking-i_mmap_mutex-in-unmap_single_vma-for-hugetlb.patch
hugetlb-simplify-migrate_huge_page.patch
hugetlb-add-a-list-for-tracking-in-use-hugetlb-pages.patch
hugetlb-make-some-static-variables-global.patch
mm-hugetlb-add-new-hugetlb-cgroup.patch
mm-hugetlb-add-new-hugetlb-cgroup-fix.patch
mm-hugetlb-add-new-hugetlb-cgroup-fix-fix.patch
hugetlb-cgroup-add-the-cgroup-pointer-to-page-lru.patch
hugetlb-cgroup-add-charge-uncharge-routines-for-hugetlb-cgroup.patch
hugetlb-cgroup-add-support-for-cgroup-removal.patch
hugetlb-cgroup-add-hugetlb-cgroup-control-files.patch
hugetlb-cgroup-add-hugetlb-cgroup-control-files-fix.patch
hugetlb-cgroup-add-hugetlb-cgroup-control-files-fix-fix.patch
hugetlb-cgroup-migrate-hugetlb-cgroup-info-from-oldpage-to-new-page-during-migration.patch
hugetlb-cgroup-add-hugetlb-controller-documentation.patch
mm-oom-do-not-schedule-if-current-has-been-killed.patch
mm-compaction-cleanup-on-compaction_deferred.patch
mm-clear-pages_scanned-only-if-draining-a-pcp-adds-pages-to-the-buddy-allocator-again.patch
mm-oom-fix-potential-killing-of-thread-that-is-disabled-from-oom-killing.patch
mm-oom-replace-some-information-in-tasklist-dump.patch
memcg-rename-config-variables.patch
memcg-rename-config-variables-fix.patch
memcg-rename-config-variables-fix-fix.patch
mm-setup-pageblock_order-before-its-used-by-sparsemem.patch
mm-hotplug-correctly-setup-fallback-zonelists-when-creating-new-pgdat.patch
mm-hotplug-correctly-add-new-zone-to-all-other-nodes-zone-lists.patch
mm-hotplug-free-zone-pageset-when-a-zone-becomes-empty.patch
mm-hotplug-mark-memory-hotplug-code-in-page_allocc-as-__meminit.patch
mm-oom-move-declaration-for-mem_cgroup_out_of_memory-to-oomh.patch
mm-oom-introduce-helper-function-to-process-threads-during-scan.patch
mm-memcg-introduce-own-oom-handler-to-iterate-only-over-its-own-threads.patch
mm-oom-reduce-dependency-on-tasklist_lock.patch
mm-memcg-move-all-oom-handling-to-memcontrolc.patch
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