From: Shakeel Butt shakeelb@google.com
mainline inclusion from mainline-5.1-rc1 commit bbbe48029720d2c6b6733f78d02571a281511adb category: bugfix bugzilla: 34611 CVE: NA
------------------------------------------------- Since the start of the git history of Linux, the kernel after selecting the worst process to be oom-killed, prefer to kill its child (if the child does not share mm with the parent). Later it was changed to prefer to kill a child who is worst. If the parent is still the worst then the parent will be killed.
This heuristic assumes that the children did less work than their parent and by killing one of them, the work lost will be less. However this is very workload dependent. If there is a workload which can benefit from this heuristic, can use oom_score_adj to prefer children to be killed before the parent.
The select_bad_process() has already selected the worst process in the system/memcg. There is no need to recheck the badness of its children and hoping to find a worse candidate. That's a lot of unneeded racy work. Also the heuristic is dangerous because it make fork bomb like workloads to recover much later because we constantly pick and kill processes which are not memory hogs. So, let's remove this whole heuristic.
[akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/20190121215850.221745-2-shakeelb@google.com Signed-off-by: Shakeel Butt shakeelb@google.com Acked-by: Michal Hocko mhocko@suse.com Acked-by: Roman Gushchin guro@fb.com Acked-by: Johannes Weiner hannes@cmpxchg.org Cc: David Rientjes rientjes@google.com Cc: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org (cherry picked from commit bbbe48029720d2c6b6733f78d02571a281511adb) Signed-off-by: Kefeng Wang wangkefeng.wang@huawei.com Signed-off-by: Liu Shixin liushixin2@huawei.com Reviewed-by: Kefeng Wang wangkefeng.wang@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- mm/oom_kill.c | 78 ++++++++++++--------------------------------------- 1 file changed, 18 insertions(+), 60 deletions(-)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 05e4ec14b588..55410ef265d6 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -842,7 +842,7 @@ static bool task_will_free_mem(struct task_struct *task) return ret; }
-static void __oom_kill_process(struct task_struct *victim) +static void __oom_kill_process(struct task_struct *victim, const char *message) { struct task_struct *p; struct mm_struct *mm; @@ -873,8 +873,9 @@ static void __oom_kill_process(struct task_struct *victim) */ do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, PIDTYPE_TGID); mark_oom_victim(victim); - pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n", - task_pid_nr(victim), victim->comm, K(victim->mm->total_vm), + pr_err("%s: Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n", + message, task_pid_nr(victim), victim->comm, + K(victim->mm->total_vm), K(get_mm_counter(victim->mm, MM_ANONPAGES)), K(get_mm_counter(victim->mm, MM_FILEPAGES)), K(get_mm_counter(victim->mm, MM_SHMEMPAGES))); @@ -925,25 +926,20 @@ static void __oom_kill_process(struct task_struct *victim) * Kill provided task unless it's secured by setting * oom_score_adj to OOM_SCORE_ADJ_MIN. */ -static int oom_kill_memcg_member(struct task_struct *task, void *unused) +static int oom_kill_memcg_member(struct task_struct *task, void *message) { if (task->signal->oom_score_adj != OOM_SCORE_ADJ_MIN && !is_global_init(task)) { get_task_struct(task); - __oom_kill_process(task); + __oom_kill_process(task, message); } return 0; }
static void oom_kill_process(struct oom_control *oc, const char *message) { - struct task_struct *p = oc->chosen; - unsigned int points = oc->chosen_points; - struct task_struct *victim = p; - struct task_struct *child; - struct task_struct *t; + struct task_struct *victim = oc->chosen; struct mem_cgroup *oom_group; - unsigned int victim_points = 0; static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL, DEFAULT_RATELIMIT_BURST);
@@ -952,57 +948,18 @@ static void oom_kill_process(struct oom_control *oc, const char *message) * its children or threads, just give it access to memory reserves * so it can die quickly */ - task_lock(p); - if (task_will_free_mem(p)) { - mark_oom_victim(p); - wake_oom_reaper(p); - task_unlock(p); - put_task_struct(p); + task_lock(victim); + if (task_will_free_mem(victim)) { + mark_oom_victim(victim); + wake_oom_reaper(victim); + task_unlock(victim); + put_task_struct(victim); return; } - task_unlock(p); + task_unlock(victim);
if (__ratelimit(&oom_rs)) - dump_header(oc, p); - - pr_err("%s: Kill process %d (%s) score %u or sacrifice child\n", - message, task_pid_nr(p), p->comm, points); - - /* - * If any of p's children has a different mm and is eligible for kill, - * the one with the highest oom_badness() score is sacrificed for its - * parent. This attempts to lose the minimal amount of work done while - * still freeing memory. - */ - read_lock(&tasklist_lock); - - /* - * The task 'p' might have already exited before reaching here. The - * put_task_struct() will free task_struct 'p' while the loop still try - * to access the field of 'p', so, get an extra reference. - */ - get_task_struct(p); - for_each_thread(p, t) { - list_for_each_entry(child, &t->children, sibling) { - unsigned int child_points; - - if (process_shares_mm(child, p->mm)) - continue; - /* - * oom_badness() returns 0 if the thread is unkillable - */ - child_points = oom_badness(child, - oc->memcg, oc->nodemask, oc->totalpages); - if (child_points > victim_points) { - put_task_struct(victim); - victim = child; - victim_points = child_points; - get_task_struct(victim); - } - } - } - put_task_struct(p); - read_unlock(&tasklist_lock); + dump_header(oc, victim);
/* * Do we need to kill the entire memory cgroup? @@ -1011,14 +968,15 @@ static void oom_kill_process(struct oom_control *oc, const char *message) */ oom_group = mem_cgroup_get_oom_group(victim, oc->memcg);
- __oom_kill_process(victim); + __oom_kill_process(victim, message);
/* * If necessary, kill all tasks in the selected memory cgroup. */ if (oom_group) { mem_cgroup_print_oom_group(oom_group); - mem_cgroup_scan_tasks(oom_group, oom_kill_memcg_member, NULL); + mem_cgroup_scan_tasks(oom_group, oom_kill_memcg_member, + (void*)message); mem_cgroup_put(oom_group); } }