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Biederman" , gladkov.alexey@gmail.com, Michel Lespinasse , daniel.m.jordan@oracle.com, avagin@gmail.com, bernd.edlinger@hotmail.de, John Johansen , laoar.shao@gmail.com, Tim Murray , Minchan Kim , kernel-team , LKML , linux-fsdevel@vger.kernel.org, stable , linux-mm , Michal Hocko Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 1D8A61A4A5 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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.GI5033@dhcp22.suse.cz/ > > - Updated description to reflect the change > > > > v1: > > - https://lore.kernel.org/linux-mm/20200820002053.1424000-1-surenb@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(&oom_adj_mutex); > > + mutex_lock(&oom_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(&p->mm->mm_users) > 1) { > > + if (test_bit(MMF_PROC_SHARED, &p->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(&oom_adj_mutex); > > + mutex_unlock(&oom_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) > > { > > diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h > > index ecdc6542070f..070629b722df 100644 > > --- a/include/linux/sched/coredump.h > > +++ b/include/linux/sched/coredump.h > > @@ -72,6 +72,7 @@ static inline int get_dumpable(struct mm_struct *mm) > > #define MMF_DISABLE_THP 24 /* disable THP for all VMAs */ > > #define MMF_OOM_VICTIM 25 /* mm is the oom victim */ > > #define MMF_OOM_REAP_QUEUED 26 /* mm was queued for oom_reaper */ > > +#define MMF_PROC_SHARED 27 /* mm is shared while sighand is not */ > > #define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP) > > > > #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\ > > diff --git a/kernel/fork.c b/kernel/fork.c > > index 4d32190861bd..6fce8ffa9b8b 100644 > > --- a/kernel/fork.c > > +++ b/kernel/fork.c > > @@ -1809,6 +1809,25 @@ static __always_inline void delayed_free_task(struct task_struct *tsk) > > free_task(tsk); > > } > > > > +static void copy_oom_score_adj(u64 clone_flags, struct task_struct *tsk) > > +{ > > + /* Skip if kernel thread */ > > + if (!tsk->mm) > > + return; > > Hm, wouldn't > > if (tsk->flags & PF_KTHREAD) > return; > > be clearer and more future proof? The check follows a similar pattern from copy_mm to detect when we are cloning a kernel thread. Also IMHO this is a more obvious way to protect from dereferencing a NULL tsk->mm, which is the important point here. I can change or remove the comment if that makes things more clear. Please LMK if that would help. > > Christian