Re: [PATCH v2 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary
On Tue 25-08-20 10:36:45, Suren Baghdasaryan wrote:
> On Tue, Aug 25, 2020 at 9:38 AM Eric W. Biederman
> wrote:
[...]
> > > diff --git a/include/linux/oom.h b/include/linux/oom.h
> > > index f022f581ac29..861f22bd4706 100644
> > > --- a/include/linux/oom.h
> > > +++ b/include/linux/oom.h
> > > @@ -55,6 +55,7 @@ struct oom_control {
> > > };
> > >
> > > extern struct mutex oom_lock;
> > > +extern struct mutex oom_adj_lock;
> >^^
> >
> > I understand moving this lock by why renaming it?
>
> To be consistent with the mutex name right above it. I'm ok keeping it
> as before if this is too much additional churn. I guess Michal deals
> with this code more than anyone else, so I'll wait for him to comment
> on this one.
I cannot say I would care deeply about naming. Consistency looks nice
but if there is a preference to keep the lock then I will not object.
--
Michal Hocko
SUSE Labs
Re: [PATCH v2 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary
On Tue, Aug 25, 2020 at 9:38 AM Eric W. Biederman wrote:
>
> Suren Baghdasaryan writes:
>
> > Currently __set_oom_adj loops through all processes in the system to
> > keep oom_score_adj and oom_score_adj_min in sync between processes
> > sharing their mm. This is done for any task with more that one mm_users,
> > which includes processes with multiple threads (sharing mm and signals).
> > However for such processes the loop is unnecessary because their signal
> > structure is shared as well.
> > Android updates oom_score_adj whenever a tasks changes its role
> > (background/foreground/...) or binds to/unbinds from a service, making
> > it more/less important. Such operation can happen frequently.
> > We noticed that updates to oom_score_adj became more expensive and after
> > further investigation found out that the patch mentioned in "Fixes"
> > introduced a regression. Using Pixel 4 with a typical Android workload,
> > write time to oom_score_adj increased from ~3.57us to ~362us. Moreover
> > this regression linearly depends on the number of multi-threaded
> > processes running on the system.
> > Mark the mm with a new MMF_PROC_SHARED flag bit when task is created with
> > (CLONE_VM && !CLONE_THREAD && !CLONE_VFORK). Change __set_oom_adj to use
> > MMF_PROC_SHARED instead of mm_users to decide whether oom_score_adj
> > update should be synchronized between multiple processes. To prevent
> > races between clone() and __set_oom_adj(), when oom_score_adj of the
> > process being cloned might be modified from userspace, we use
> > oom_adj_mutex. Its scope is changed to global and it is renamed into
> > oom_adj_lock for naming consistency with oom_lock. The combination of
> > (CLONE_VM && !CLONE_THREAD) is rarely used except for the case of vfork().
> > To prevent performance regressions of vfork(), we skip taking oom_adj_lock
> > and setting MMF_PROC_SHARED when CLONE_VFORK is specified. Clearing the
> > MMF_PROC_SHARED flag (when the last process sharing the mm exits) is left
> > out of this patch to keep it simple and because it is believed that this
> > threading model is rare. Should there ever be a need for optimizing that
> > case as well, it can be done by hooking into the exit path, likely
> > following the mm_update_next_owner pattern.
> > With the combination of (CLONE_VM && !CLONE_THREAD && !CLONE_VFORK) being
> > quite rare, the regression is gone after the change is applied.
>
> This patch still makes my head hurt.
Sorry about that. It was not my intention and I wish there was a
simpler way to do this.
>
> The obvious wrong things I have mentioned below.
>
>
> > Fixes: 44a70adec910 ("mm, oom_adj: make sure processes sharing mm have same
> > view of oom_score_adj")
> > Reported-by: Tim Murray
> > Debugged-by: Minchan Kim
> > Suggested-by: Michal Hocko
> > Signed-off-by: Suren Baghdasaryan
> > ---
> >
> > v2:
> > - Implemented proposal from Michal Hocko in:
> > https://lore.kernel.org/linux-fsdevel/20200820124109.gi5...@dhcp22.suse.cz/
> > - Updated description to reflect the change
> >
> > v1:
> > -
> > https://lore.kernel.org/linux-mm/20200820002053.1424000-1-sur...@google.com/
> >
> > fs/proc/base.c | 7 +++
> > include/linux/oom.h| 1 +
> > include/linux/sched/coredump.h | 1 +
> > kernel/fork.c | 21 +
> > mm/oom_kill.c | 2 ++
> > 5 files changed, 28 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > index 617db4e0faa0..cff1a58a236c 100644
> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> > @@ -1055,7 +1055,6 @@ static ssize_t oom_adj_read(struct file *file, char
> > __user *buf, size_t count,
> >
> > static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
> > {
> > - static DEFINE_MUTEX(oom_adj_mutex);
> > struct mm_struct *mm = NULL;
> > struct task_struct *task;
> > int err = 0;
> > @@ -1064,7 +1063,7 @@ static int __set_oom_adj(struct file *file, int
> > oom_adj, bool legacy)
> > if (!task)
> > return -ESRCH;
> >
> > - mutex_lock(_adj_mutex);
> > + mutex_lock(_adj_lock);
> > if (legacy) {
> > if (oom_adj < task->signal->oom_score_adj &&
> > !capable(CAP_SYS_RESOURCE)) {
> > @@ -1095,7 +1094,7 @@ static int __set_oom_adj(struct file *file, int
> > oom_adj, bool legacy)
> > struct task_struct *p = find_lock_task_mm(task);
> >
> > if (p) {
> > - if (atomic_read(>mm->mm_users) > 1) {
> > + if (test_bit(MMF_PROC_SHARED, >mm->flags)) {
> > mm = p->mm;
> > mmgrab(mm);
> > }
> > @@ -1132,7 +1131,7 @@ static int __set_oom_adj(struct file *file, int
> > oom_adj, bool legacy)
> > mmdrop(mm);
> > }
> > err_unlock:
> > - mutex_unlock(_adj_mutex);
> > +
Re: [PATCH v2 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary
Suren Baghdasaryan writes:
> Currently __set_oom_adj loops through all processes in the system to
> keep oom_score_adj and oom_score_adj_min in sync between processes
> sharing their mm. This is done for any task with more that one mm_users,
> which includes processes with multiple threads (sharing mm and signals).
> However for such processes the loop is unnecessary because their signal
> structure is shared as well.
> Android updates oom_score_adj whenever a tasks changes its role
> (background/foreground/...) or binds to/unbinds from a service, making
> it more/less important. Such operation can happen frequently.
> We noticed that updates to oom_score_adj became more expensive and after
> further investigation found out that the patch mentioned in "Fixes"
> introduced a regression. Using Pixel 4 with a typical Android workload,
> write time to oom_score_adj increased from ~3.57us to ~362us. Moreover
> this regression linearly depends on the number of multi-threaded
> processes running on the system.
> Mark the mm with a new MMF_PROC_SHARED flag bit when task is created with
> (CLONE_VM && !CLONE_THREAD && !CLONE_VFORK). Change __set_oom_adj to use
> MMF_PROC_SHARED instead of mm_users to decide whether oom_score_adj
> update should be synchronized between multiple processes. To prevent
> races between clone() and __set_oom_adj(), when oom_score_adj of the
> process being cloned might be modified from userspace, we use
> oom_adj_mutex. Its scope is changed to global and it is renamed into
> oom_adj_lock for naming consistency with oom_lock. The combination of
> (CLONE_VM && !CLONE_THREAD) is rarely used except for the case of vfork().
> To prevent performance regressions of vfork(), we skip taking oom_adj_lock
> and setting MMF_PROC_SHARED when CLONE_VFORK is specified. Clearing the
> MMF_PROC_SHARED flag (when the last process sharing the mm exits) is left
> out of this patch to keep it simple and because it is believed that this
> threading model is rare. Should there ever be a need for optimizing that
> case as well, it can be done by hooking into the exit path, likely
> following the mm_update_next_owner pattern.
> With the combination of (CLONE_VM && !CLONE_THREAD && !CLONE_VFORK) being
> quite rare, the regression is gone after the change is applied.
This patch still makes my head hurt.
The obvious wrong things I have mentioned below.
> Fixes: 44a70adec910 ("mm, oom_adj: make sure processes sharing mm have same
> view of oom_score_adj")
> Reported-by: Tim Murray
> Debugged-by: Minchan Kim
> Suggested-by: Michal Hocko
> Signed-off-by: Suren Baghdasaryan
> ---
>
> v2:
> - Implemented proposal from Michal Hocko in:
> https://lore.kernel.org/linux-fsdevel/20200820124109.gi5...@dhcp22.suse.cz/
> - Updated description to reflect the change
>
> v1:
> - https://lore.kernel.org/linux-mm/20200820002053.1424000-1-sur...@google.com/
>
> fs/proc/base.c | 7 +++
> include/linux/oom.h| 1 +
> include/linux/sched/coredump.h | 1 +
> kernel/fork.c | 21 +
> mm/oom_kill.c | 2 ++
> 5 files changed, 28 insertions(+), 4 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 617db4e0faa0..cff1a58a236c 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1055,7 +1055,6 @@ static ssize_t oom_adj_read(struct file *file, char
> __user *buf, size_t count,
>
> static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
> {
> - static DEFINE_MUTEX(oom_adj_mutex);
> struct mm_struct *mm = NULL;
> struct task_struct *task;
> int err = 0;
> @@ -1064,7 +1063,7 @@ static int __set_oom_adj(struct file *file, int
> oom_adj, bool legacy)
> if (!task)
> return -ESRCH;
>
> - mutex_lock(_adj_mutex);
> + mutex_lock(_adj_lock);
> if (legacy) {
> if (oom_adj < task->signal->oom_score_adj &&
> !capable(CAP_SYS_RESOURCE)) {
> @@ -1095,7 +1094,7 @@ static int __set_oom_adj(struct file *file, int
> oom_adj, bool legacy)
> struct task_struct *p = find_lock_task_mm(task);
>
> if (p) {
> - if (atomic_read(>mm->mm_users) > 1) {
> + if (test_bit(MMF_PROC_SHARED, >mm->flags)) {
> mm = p->mm;
> mmgrab(mm);
> }
> @@ -1132,7 +1131,7 @@ static int __set_oom_adj(struct file *file, int
> oom_adj, bool legacy)
> mmdrop(mm);
> }
> err_unlock:
> - mutex_unlock(_adj_mutex);
> + mutex_unlock(_adj_lock);
> put_task_struct(task);
> return err;
> }
> diff --git a/include/linux/oom.h b/include/linux/oom.h
> index f022f581ac29..861f22bd4706 100644
> --- a/include/linux/oom.h
> +++ b/include/linux/oom.h
> @@ -55,6 +55,7 @@ struct oom_control {
> };
>
> extern struct mutex oom_lock;
> +extern struct mutex oom_adj_lock;
Re: [PATCH v2 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary
On 08/25, Michal Hocko wrote: > > Btw. now that the flag is in place we can optimize __oom_kill_process as > well. and zap_threads(). Oleg.
Re: [PATCH v2 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary
On Mon 24-08-20 08:30:36, Suren Baghdasaryan wrote:
> Currently __set_oom_adj loops through all processes in the system to
> keep oom_score_adj and oom_score_adj_min in sync between processes
> sharing their mm. This is done for any task with more that one mm_users,
> which includes processes with multiple threads (sharing mm and signals).
> However for such processes the loop is unnecessary because their signal
> structure is shared as well.
> Android updates oom_score_adj whenever a tasks changes its role
> (background/foreground/...) or binds to/unbinds from a service, making
> it more/less important. Such operation can happen frequently.
> We noticed that updates to oom_score_adj became more expensive and after
> further investigation found out that the patch mentioned in "Fixes"
> introduced a regression. Using Pixel 4 with a typical Android workload,
> write time to oom_score_adj increased from ~3.57us to ~362us. Moreover
> this regression linearly depends on the number of multi-threaded
> processes running on the system.
> Mark the mm with a new MMF_PROC_SHARED flag bit when task is created with
> (CLONE_VM && !CLONE_THREAD && !CLONE_VFORK). Change __set_oom_adj to use
> MMF_PROC_SHARED instead of mm_users to decide whether oom_score_adj
> update should be synchronized between multiple processes. To prevent
> races between clone() and __set_oom_adj(), when oom_score_adj of the
> process being cloned might be modified from userspace, we use
> oom_adj_mutex. Its scope is changed to global and it is renamed into
> oom_adj_lock for naming consistency with oom_lock. The combination of
> (CLONE_VM && !CLONE_THREAD) is rarely used except for the case of vfork().
> To prevent performance regressions of vfork(), we skip taking oom_adj_lock
> and setting MMF_PROC_SHARED when CLONE_VFORK is specified. Clearing the
> MMF_PROC_SHARED flag (when the last process sharing the mm exits) is left
> out of this patch to keep it simple and because it is believed that this
> threading model is rare. Should there ever be a need for optimizing that
> case as well, it can be done by hooking into the exit path, likely
> following the mm_update_next_owner pattern.
> With the combination of (CLONE_VM && !CLONE_THREAD && !CLONE_VFORK) being
> quite rare, the regression is gone after the change is applied.
>
> Fixes: 44a70adec910 ("mm, oom_adj: make sure processes sharing mm have same
> view of oom_score_adj")
> Reported-by: Tim Murray
> Debugged-by: Minchan Kim
> Suggested-by: Michal Hocko
> Signed-off-by: Suren Baghdasaryan
Acked-by: Michal Hocko
I hope we can build on top of this and move oom_core* stuff to the
mm_struct to remove all this cruft but I still think that this is
conceptually easier to backport to older kernels than a completely new
approach.
Btw. now that the flag is in place we can optimize __oom_kill_process as
well. Not that this particular path is performance sensitive. But it
could show up in group oom killing in memcgs. It should be as simple as
(I can prepare an official patch unless somebody beat me to it)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index c22f07c986cb..04cf958d0c29 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -906,29 +906,31 @@ static void __oom_kill_process(struct task_struct
*victim, const char *message)
* That thread will now get access to memory reserves since it has a
* pending fatal signal.
*/
- rcu_read_lock();
- for_each_process(p) {
- if (!process_shares_mm(p, mm))
- continue;
- if (same_thread_group(p, victim))
- continue;
- if (is_global_init(p)) {
- can_oom_reap = false;
- set_bit(MMF_OOM_SKIP, >flags);
- pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n",
- task_pid_nr(victim), victim->comm,
- task_pid_nr(p), p->comm);
- continue;
+ if (test_bit(MMF_PROC_SHARED, >mm->flags)) {
+ rcu_read_lock();
+ for_each_process(p) {
+ if (!process_shares_mm(p, mm))
+ continue;
+ if (same_thread_group(p, victim))
+ continue;
+ if (is_global_init(p)) {
+ can_oom_reap = false;
+ set_bit(MMF_OOM_SKIP, >flags);
+ pr_info("oom killer %d (%s) has mm pinned by %d
(%s)\n",
+ task_pid_nr(victim),
victim->comm,
+ task_pid_nr(p), p->comm);
+ continue;
+ }
+ /*
+* No kthead_use_mm() user needs to read from the
userspace so
+* we are ok to
Re: [PATCH v2 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary
On Tue, Aug 25, 2020 at 07:24:34AM -0700, Suren Baghdasaryan wrote:
> On Tue, Aug 25, 2020 at 4:15 AM Christian Brauner
> wrote:
> >
> > On Mon, Aug 24, 2020 at 08:30:36AM -0700, Suren Baghdasaryan wrote:
> > > Currently __set_oom_adj loops through all processes in the system to
> > > keep oom_score_adj and oom_score_adj_min in sync between processes
> > > sharing their mm. This is done for any task with more that one mm_users,
> > > which includes processes with multiple threads (sharing mm and signals).
> > > However for such processes the loop is unnecessary because their signal
> > > structure is shared as well.
> > > Android updates oom_score_adj whenever a tasks changes its role
> > > (background/foreground/...) or binds to/unbinds from a service, making
> > > it more/less important. Such operation can happen frequently.
> > > We noticed that updates to oom_score_adj became more expensive and after
> > > further investigation found out that the patch mentioned in "Fixes"
> > > introduced a regression. Using Pixel 4 with a typical Android workload,
> > > write time to oom_score_adj increased from ~3.57us to ~362us. Moreover
> > > this regression linearly depends on the number of multi-threaded
> > > processes running on the system.
> > > Mark the mm with a new MMF_PROC_SHARED flag bit when task is created with
> > > (CLONE_VM && !CLONE_THREAD && !CLONE_VFORK). Change __set_oom_adj to use
> > > MMF_PROC_SHARED instead of mm_users to decide whether oom_score_adj
> > > update should be synchronized between multiple processes. To prevent
> > > races between clone() and __set_oom_adj(), when oom_score_adj of the
> > > process being cloned might be modified from userspace, we use
> > > oom_adj_mutex. Its scope is changed to global and it is renamed into
> > > oom_adj_lock for naming consistency with oom_lock. The combination of
> > > (CLONE_VM && !CLONE_THREAD) is rarely used except for the case of vfork().
> > > To prevent performance regressions of vfork(), we skip taking oom_adj_lock
> > > and setting MMF_PROC_SHARED when CLONE_VFORK is specified. Clearing the
> > > MMF_PROC_SHARED flag (when the last process sharing the mm exits) is left
> > > out of this patch to keep it simple and because it is believed that this
> > > threading model is rare. Should there ever be a need for optimizing that
> > > case as well, it can be done by hooking into the exit path, likely
> > > following the mm_update_next_owner pattern.
> > > With the combination of (CLONE_VM && !CLONE_THREAD && !CLONE_VFORK) being
> > > quite rare, the regression is gone after the change is applied.
> > >
> > > Fixes: 44a70adec910 ("mm, oom_adj: make sure processes sharing mm have
> > > same view of oom_score_adj")
> > > Reported-by: Tim Murray
> > > Debugged-by: Minchan Kim
> > > Suggested-by: Michal Hocko
> > > Signed-off-by: Suren Baghdasaryan
> > > ---
> > >
> > > v2:
> > > - Implemented proposal from Michal Hocko in:
> > > https://lore.kernel.org/linux-fsdevel/20200820124109.gi5...@dhcp22.suse.cz/
> > > - Updated description to reflect the change
> > >
> > > v1:
> > > -
> > > https://lore.kernel.org/linux-mm/20200820002053.1424000-1-sur...@google.com/
> > >
> > > fs/proc/base.c | 7 +++
> > > include/linux/oom.h| 1 +
> > > include/linux/sched/coredump.h | 1 +
> > > kernel/fork.c | 21 +
> > > mm/oom_kill.c | 2 ++
> > > 5 files changed, 28 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > > index 617db4e0faa0..cff1a58a236c 100644
> > > --- a/fs/proc/base.c
> > > +++ b/fs/proc/base.c
> > > @@ -1055,7 +1055,6 @@ static ssize_t oom_adj_read(struct file *file, char
> > > __user *buf, size_t count,
> > >
> > > static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
> > > {
> > > - static DEFINE_MUTEX(oom_adj_mutex);
> > > struct mm_struct *mm = NULL;
> > > struct task_struct *task;
> > > int err = 0;
> > > @@ -1064,7 +1063,7 @@ static int __set_oom_adj(struct file *file, int
> > > oom_adj, bool legacy)
> > > if (!task)
> > > return -ESRCH;
> > >
> > > - mutex_lock(_adj_mutex);
> > > + mutex_lock(_adj_lock);
> > > if (legacy) {
> > > if (oom_adj < task->signal->oom_score_adj &&
> > > !capable(CAP_SYS_RESOURCE)) {
> > > @@ -1095,7 +1094,7 @@ static int __set_oom_adj(struct file *file, int
> > > oom_adj, bool legacy)
> > > struct task_struct *p = find_lock_task_mm(task);
> > >
> > > if (p) {
> > > - if (atomic_read(>mm->mm_users) > 1) {
> > > + if (test_bit(MMF_PROC_SHARED, >mm->flags)) {
> > > mm = p->mm;
> > > mmgrab(mm);
> > > }
> > > @@ -1132,7 +1131,7 @@ static int __set_oom_adj(struct file *file, int
> > > oom_adj, bool legacy)
> > >
Re: [PATCH v2 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary
On 08/24, Suren Baghdasaryan wrote: > > v2: > - Implemented proposal from Michal Hocko in: > https://lore.kernel.org/linux-fsdevel/20200820124109.gi5...@dhcp22.suse.cz/ > - Updated description to reflect the change Looks good to me, Oleg.
Re: [PATCH v2 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary
On Tue, Aug 25, 2020 at 4:15 AM Christian Brauner
wrote:
>
> On Mon, Aug 24, 2020 at 08:30:36AM -0700, Suren Baghdasaryan wrote:
> > Currently __set_oom_adj loops through all processes in the system to
> > keep oom_score_adj and oom_score_adj_min in sync between processes
> > sharing their mm. This is done for any task with more that one mm_users,
> > which includes processes with multiple threads (sharing mm and signals).
> > However for such processes the loop is unnecessary because their signal
> > structure is shared as well.
> > Android updates oom_score_adj whenever a tasks changes its role
> > (background/foreground/...) or binds to/unbinds from a service, making
> > it more/less important. Such operation can happen frequently.
> > We noticed that updates to oom_score_adj became more expensive and after
> > further investigation found out that the patch mentioned in "Fixes"
> > introduced a regression. Using Pixel 4 with a typical Android workload,
> > write time to oom_score_adj increased from ~3.57us to ~362us. Moreover
> > this regression linearly depends on the number of multi-threaded
> > processes running on the system.
> > Mark the mm with a new MMF_PROC_SHARED flag bit when task is created with
> > (CLONE_VM && !CLONE_THREAD && !CLONE_VFORK). Change __set_oom_adj to use
> > MMF_PROC_SHARED instead of mm_users to decide whether oom_score_adj
> > update should be synchronized between multiple processes. To prevent
> > races between clone() and __set_oom_adj(), when oom_score_adj of the
> > process being cloned might be modified from userspace, we use
> > oom_adj_mutex. Its scope is changed to global and it is renamed into
> > oom_adj_lock for naming consistency with oom_lock. The combination of
> > (CLONE_VM && !CLONE_THREAD) is rarely used except for the case of vfork().
> > To prevent performance regressions of vfork(), we skip taking oom_adj_lock
> > and setting MMF_PROC_SHARED when CLONE_VFORK is specified. Clearing the
> > MMF_PROC_SHARED flag (when the last process sharing the mm exits) is left
> > out of this patch to keep it simple and because it is believed that this
> > threading model is rare. Should there ever be a need for optimizing that
> > case as well, it can be done by hooking into the exit path, likely
> > following the mm_update_next_owner pattern.
> > With the combination of (CLONE_VM && !CLONE_THREAD && !CLONE_VFORK) being
> > quite rare, the regression is gone after the change is applied.
> >
> > Fixes: 44a70adec910 ("mm, oom_adj: make sure processes sharing mm have same
> > view of oom_score_adj")
> > Reported-by: Tim Murray
> > Debugged-by: Minchan Kim
> > Suggested-by: Michal Hocko
> > Signed-off-by: Suren Baghdasaryan
> > ---
> >
> > v2:
> > - Implemented proposal from Michal Hocko in:
> > https://lore.kernel.org/linux-fsdevel/20200820124109.gi5...@dhcp22.suse.cz/
> > - Updated description to reflect the change
> >
> > v1:
> > -
> > https://lore.kernel.org/linux-mm/20200820002053.1424000-1-sur...@google.com/
> >
> > fs/proc/base.c | 7 +++
> > include/linux/oom.h| 1 +
> > include/linux/sched/coredump.h | 1 +
> > kernel/fork.c | 21 +
> > mm/oom_kill.c | 2 ++
> > 5 files changed, 28 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > index 617db4e0faa0..cff1a58a236c 100644
> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> > @@ -1055,7 +1055,6 @@ static ssize_t oom_adj_read(struct file *file, char
> > __user *buf, size_t count,
> >
> > static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
> > {
> > - static DEFINE_MUTEX(oom_adj_mutex);
> > struct mm_struct *mm = NULL;
> > struct task_struct *task;
> > int err = 0;
> > @@ -1064,7 +1063,7 @@ static int __set_oom_adj(struct file *file, int
> > oom_adj, bool legacy)
> > if (!task)
> > return -ESRCH;
> >
> > - mutex_lock(_adj_mutex);
> > + mutex_lock(_adj_lock);
> > if (legacy) {
> > if (oom_adj < task->signal->oom_score_adj &&
> > !capable(CAP_SYS_RESOURCE)) {
> > @@ -1095,7 +1094,7 @@ static int __set_oom_adj(struct file *file, int
> > oom_adj, bool legacy)
> > struct task_struct *p = find_lock_task_mm(task);
> >
> > if (p) {
> > - if (atomic_read(>mm->mm_users) > 1) {
> > + if (test_bit(MMF_PROC_SHARED, >mm->flags)) {
> > mm = p->mm;
> > mmgrab(mm);
> > }
> > @@ -1132,7 +1131,7 @@ static int __set_oom_adj(struct file *file, int
> > oom_adj, bool legacy)
> > mmdrop(mm);
> > }
> > err_unlock:
> > - mutex_unlock(_adj_mutex);
> > + mutex_unlock(_adj_lock);
> > put_task_struct(task);
> > return err;
> > }
> > diff --git a/include/linux/oom.h b/include/linux/oom.h
> > index
Re: [PATCH v2 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary
On Mon, Aug 24, 2020 at 08:30:36AM -0700, Suren Baghdasaryan wrote:
> Currently __set_oom_adj loops through all processes in the system to
> keep oom_score_adj and oom_score_adj_min in sync between processes
> sharing their mm. This is done for any task with more that one mm_users,
> which includes processes with multiple threads (sharing mm and signals).
> However for such processes the loop is unnecessary because their signal
> structure is shared as well.
> Android updates oom_score_adj whenever a tasks changes its role
> (background/foreground/...) or binds to/unbinds from a service, making
> it more/less important. Such operation can happen frequently.
> We noticed that updates to oom_score_adj became more expensive and after
> further investigation found out that the patch mentioned in "Fixes"
> introduced a regression. Using Pixel 4 with a typical Android workload,
> write time to oom_score_adj increased from ~3.57us to ~362us. Moreover
> this regression linearly depends on the number of multi-threaded
> processes running on the system.
> Mark the mm with a new MMF_PROC_SHARED flag bit when task is created with
> (CLONE_VM && !CLONE_THREAD && !CLONE_VFORK). Change __set_oom_adj to use
> MMF_PROC_SHARED instead of mm_users to decide whether oom_score_adj
> update should be synchronized between multiple processes. To prevent
> races between clone() and __set_oom_adj(), when oom_score_adj of the
> process being cloned might be modified from userspace, we use
> oom_adj_mutex. Its scope is changed to global and it is renamed into
> oom_adj_lock for naming consistency with oom_lock. The combination of
> (CLONE_VM && !CLONE_THREAD) is rarely used except for the case of vfork().
> To prevent performance regressions of vfork(), we skip taking oom_adj_lock
> and setting MMF_PROC_SHARED when CLONE_VFORK is specified. Clearing the
> MMF_PROC_SHARED flag (when the last process sharing the mm exits) is left
> out of this patch to keep it simple and because it is believed that this
> threading model is rare. Should there ever be a need for optimizing that
> case as well, it can be done by hooking into the exit path, likely
> following the mm_update_next_owner pattern.
> With the combination of (CLONE_VM && !CLONE_THREAD && !CLONE_VFORK) being
> quite rare, the regression is gone after the change is applied.
>
> Fixes: 44a70adec910 ("mm, oom_adj: make sure processes sharing mm have same
> view of oom_score_adj")
> Reported-by: Tim Murray
> Debugged-by: Minchan Kim
> Suggested-by: Michal Hocko
> Signed-off-by: Suren Baghdasaryan
> ---
>
> v2:
> - Implemented proposal from Michal Hocko in:
> https://lore.kernel.org/linux-fsdevel/20200820124109.gi5...@dhcp22.suse.cz/
> - Updated description to reflect the change
>
> v1:
> - https://lore.kernel.org/linux-mm/20200820002053.1424000-1-sur...@google.com/
>
> fs/proc/base.c | 7 +++
> include/linux/oom.h| 1 +
> include/linux/sched/coredump.h | 1 +
> kernel/fork.c | 21 +
> mm/oom_kill.c | 2 ++
> 5 files changed, 28 insertions(+), 4 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 617db4e0faa0..cff1a58a236c 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1055,7 +1055,6 @@ static ssize_t oom_adj_read(struct file *file, char
> __user *buf, size_t count,
>
> static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
> {
> - static DEFINE_MUTEX(oom_adj_mutex);
> struct mm_struct *mm = NULL;
> struct task_struct *task;
> int err = 0;
> @@ -1064,7 +1063,7 @@ static int __set_oom_adj(struct file *file, int
> oom_adj, bool legacy)
> if (!task)
> return -ESRCH;
>
> - mutex_lock(_adj_mutex);
> + mutex_lock(_adj_lock);
> if (legacy) {
> if (oom_adj < task->signal->oom_score_adj &&
> !capable(CAP_SYS_RESOURCE)) {
> @@ -1095,7 +1094,7 @@ static int __set_oom_adj(struct file *file, int
> oom_adj, bool legacy)
> struct task_struct *p = find_lock_task_mm(task);
>
> if (p) {
> - if (atomic_read(>mm->mm_users) > 1) {
> + if (test_bit(MMF_PROC_SHARED, >mm->flags)) {
> mm = p->mm;
> mmgrab(mm);
> }
> @@ -1132,7 +1131,7 @@ static int __set_oom_adj(struct file *file, int
> oom_adj, bool legacy)
> mmdrop(mm);
> }
> err_unlock:
> - mutex_unlock(_adj_mutex);
> + mutex_unlock(_adj_lock);
> put_task_struct(task);
> return err;
> }
> diff --git a/include/linux/oom.h b/include/linux/oom.h
> index f022f581ac29..861f22bd4706 100644
> --- a/include/linux/oom.h
> +++ b/include/linux/oom.h
> @@ -55,6 +55,7 @@ struct oom_control {
> };
>
> extern struct mutex oom_lock;
> +extern struct mutex oom_adj_lock;
>
> static inline void set_current_oom_origin(void)
>
