| Message ID | 20190121215850.221745-2-shakeelb@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | None | expand |
On Mon, Jan 21, 2019 at 1:59 PM Shakeel Butt <shakeelb@google.com> wrote: > > From 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. > > Signed-off-by: Shakeel Butt <shakeelb@google.com> > Acked-by: Michal Hocko <mhocko@suse.com> Michal, though I have kept your Acked-by but I have made a couple of changes in the code. Please let me know if you are ok with the changes. > Cc: Roman Gushchin <guro@fb.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: David Rientjes <rientjes@google.com> > Cc: Johannes Weiner <hannes@cmpxchg.org> > Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > > --- > Changelog since v2: > - Propagate the message to __oom_kill_process(). > > Changelog since v1: > - Improved commit message based on mhocko's comment. > - Replaced 'p' with 'victim'. > - Removed extra pr_err message. > > --- > 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 1a007dae1e8f..c90184fd48a3 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -843,7 +843,7 @@ 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; > @@ -874,8 +874,9 @@ static void __oom_kill_process(struct task_struct *victim) > */ > do_send_sig_info(SIGKILL, SEND_SIG_PRIV, 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))); > @@ -932,24 +933,19 @@ 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) { > 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); > > @@ -958,57 +954,18 @@ 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? > @@ -1017,14 +974,15 @@ 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); > } > } > -- > 2.20.1.321.g9e740568ce-goog >
On Mon 21-01-19 18:41:28, Shakeel Butt wrote: > On Mon, Jan 21, 2019 at 1:59 PM Shakeel Butt <shakeelb@google.com> wrote: > > > > From 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. > > > > Signed-off-by: Shakeel Butt <shakeelb@google.com> > > Acked-by: Michal Hocko <mhocko@suse.com> > > Michal, though I have kept your Acked-by but I have made a couple of > changes in the code. Please let me know if you are ok with the > changes. So the only change I can see is that we no longer print the score of the selected oom victim and that each killed task gets the oom scope prefix. I cannot think of anybody relying on the former and the later makes sense to me. So yeah, I am still OK with the resulting code. > > Cc: Roman Gushchin <guro@fb.com> > > Cc: Andrew Morton <akpm@linux-foundation.org> > > Cc: David Rientjes <rientjes@google.com> > > Cc: Johannes Weiner <hannes@cmpxchg.org> > > Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> > > Cc: linux-mm@kvack.org > > Cc: linux-kernel@vger.kernel.org > > > > --- > > Changelog since v2: > > - Propagate the message to __oom_kill_process(). > > > > Changelog since v1: > > - Improved commit message based on mhocko's comment. > > - Replaced 'p' with 'victim'. > > - Removed extra pr_err message. > > > > --- > > 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 1a007dae1e8f..c90184fd48a3 100644 > > --- a/mm/oom_kill.c > > +++ b/mm/oom_kill.c > > @@ -843,7 +843,7 @@ 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; > > @@ -874,8 +874,9 @@ static void __oom_kill_process(struct task_struct *victim) > > */ > > do_send_sig_info(SIGKILL, SEND_SIG_PRIV, 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))); > > @@ -932,24 +933,19 @@ 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) { > > 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); > > > > @@ -958,57 +954,18 @@ 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? > > @@ -1017,14 +974,15 @@ 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); > > } > > } > > -- > > 2.20.1.321.g9e740568ce-goog > >
diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 1a007dae1e8f..c90184fd48a3 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -843,7 +843,7 @@ 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; @@ -874,8 +874,9 @@ static void __oom_kill_process(struct task_struct *victim) */ do_send_sig_info(SIGKILL, SEND_SIG_PRIV, 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))); @@ -932,24 +933,19 @@ 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) { 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); @@ -958,57 +954,18 @@ 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? @@ -1017,14 +974,15 @@ 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); } }