oom: add per-mm oom disable count
It's pointless to kill a task if another thread sharing its mm cannot be killed to allow future memory freeing. A subsequent patch will prevent kills in such cases, but first it's necessary to have a way to flag a task that shares memory with an OOM_DISABLE task that doesn't incur an additional tasklist scan, which would make select_bad_process() an O(n^2) function. This patch adds an atomic counter to struct mm_struct that follows how many threads attached to it have an oom_score_adj of OOM_SCORE_ADJ_MIN. They cannot be killed by the kernel, so their memory cannot be freed in oom conditions. This only requires task_lock() on the task that we're operating on, it does not require mm->mmap_sem since task_lock() pins the mm and the operation is atomic. [rientjes@google.com: changelog and sys_unshare() code] [rientjes@google.com: protect oom_disable_count with task_lock in fork] [rientjes@google.com: use old_mm for oom_disable_count in exec] Signed-off-by: Ying Han <yinghan@google.com> Signed-off-by: David Rientjes <rientjes@google.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -54,6 +54,7 @@
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#include <linux/fsnotify.h>
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#include <linux/fs_struct.h>
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#include <linux/pipe_fs_i.h>
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#include <linux/oom.h>
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#include <asm/uaccess.h>
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#include <asm/mmu_context.h>
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@ -759,6 +760,10 @@ static int exec_mmap(struct mm_struct *mm)
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tsk->mm = mm;
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tsk->active_mm = mm;
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activate_mm(active_mm, mm);
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if (old_mm && tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
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atomic_dec(&old_mm->oom_disable_count);
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atomic_inc(&tsk->mm->oom_disable_count);
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}
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task_unlock(tsk);
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arch_pick_mmap_layout(mm);
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if (old_mm) {
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@ -1047,6 +1047,21 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
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return -EACCES;
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}
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task_lock(task);
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if (!task->mm) {
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task_unlock(task);
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unlock_task_sighand(task, &flags);
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put_task_struct(task);
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return -EINVAL;
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}
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if (oom_adjust != task->signal->oom_adj) {
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if (oom_adjust == OOM_DISABLE)
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atomic_inc(&task->mm->oom_disable_count);
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if (task->signal->oom_adj == OOM_DISABLE)
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atomic_dec(&task->mm->oom_disable_count);
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}
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/*
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* Warn that /proc/pid/oom_adj is deprecated, see
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* Documentation/feature-removal-schedule.txt.
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@ -1065,6 +1080,7 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
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else
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task->signal->oom_score_adj = (oom_adjust * OOM_SCORE_ADJ_MAX) /
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-OOM_DISABLE;
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task_unlock(task);
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unlock_task_sighand(task, &flags);
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put_task_struct(task);
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@ -1133,6 +1149,19 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
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return -EACCES;
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}
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task_lock(task);
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if (!task->mm) {
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task_unlock(task);
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unlock_task_sighand(task, &flags);
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put_task_struct(task);
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return -EINVAL;
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}
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if (oom_score_adj != task->signal->oom_score_adj) {
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if (oom_score_adj == OOM_SCORE_ADJ_MIN)
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atomic_inc(&task->mm->oom_disable_count);
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if (task->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
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atomic_dec(&task->mm->oom_disable_count);
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}
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task->signal->oom_score_adj = oom_score_adj;
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/*
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* Scale /proc/pid/oom_adj appropriately ensuring that OOM_DISABLE is
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@ -1143,6 +1172,7 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
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else
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task->signal->oom_adj = (oom_score_adj * OOM_ADJUST_MAX) /
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OOM_SCORE_ADJ_MAX;
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task_unlock(task);
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unlock_task_sighand(task, &flags);
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put_task_struct(task);
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return count;
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@ -310,6 +310,8 @@ struct mm_struct {
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#ifdef CONFIG_MMU_NOTIFIER
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struct mmu_notifier_mm *mmu_notifier_mm;
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#endif
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/* How many tasks sharing this mm are OOM_DISABLE */
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atomic_t oom_disable_count;
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};
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/* Future-safe accessor for struct mm_struct's cpu_vm_mask. */
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@ -50,6 +50,7 @@
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#include <linux/perf_event.h>
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#include <trace/events/sched.h>
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#include <linux/hw_breakpoint.h>
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#include <linux/oom.h>
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#include <asm/uaccess.h>
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#include <asm/unistd.h>
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@ -687,6 +688,8 @@ static void exit_mm(struct task_struct * tsk)
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enter_lazy_tlb(mm, current);
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/* We don't want this task to be frozen prematurely */
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clear_freeze_flag(tsk);
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if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
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atomic_dec(&mm->oom_disable_count);
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task_unlock(tsk);
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mm_update_next_owner(mm);
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mmput(mm);
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@ -65,6 +65,7 @@
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#include <linux/perf_event.h>
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#include <linux/posix-timers.h>
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#include <linux/user-return-notifier.h>
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#include <linux/oom.h>
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#include <asm/pgtable.h>
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#include <asm/pgalloc.h>
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@ -488,6 +489,7 @@ static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)
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mm->cached_hole_size = ~0UL;
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mm_init_aio(mm);
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mm_init_owner(mm, p);
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atomic_set(&mm->oom_disable_count, 0);
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if (likely(!mm_alloc_pgd(mm))) {
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mm->def_flags = 0;
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@ -741,6 +743,8 @@ good_mm:
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/* Initializing for Swap token stuff */
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mm->token_priority = 0;
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mm->last_interval = 0;
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if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
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atomic_inc(&mm->oom_disable_count);
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tsk->mm = mm;
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tsk->active_mm = mm;
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@ -1299,8 +1303,13 @@ bad_fork_cleanup_io:
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bad_fork_cleanup_namespaces:
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exit_task_namespaces(p);
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bad_fork_cleanup_mm:
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if (p->mm)
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if (p->mm) {
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task_lock(p);
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if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
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atomic_dec(&p->mm->oom_disable_count);
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task_unlock(p);
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mmput(p->mm);
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}
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bad_fork_cleanup_signal:
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if (!(clone_flags & CLONE_THREAD))
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free_signal_struct(p->signal);
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@ -1693,6 +1702,10 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
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active_mm = current->active_mm;
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current->mm = new_mm;
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current->active_mm = new_mm;
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if (current->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
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atomic_dec(&mm->oom_disable_count);
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atomic_inc(&new_mm->oom_disable_count);
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}
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activate_mm(active_mm, new_mm);
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new_mm = mm;
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}
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