Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 3d5992d2 authored by Ying Han's avatar Ying Han Committed by Linus Torvalds
Browse files

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: default avatarYing Han <yinghan@google.com>
Signed-off-by: default avatarDavid 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0f4d208f

fs/exec.c

+5 −0
Original line number Diff line number Diff line
@@ -54,6 +54,7 @@ 
#include <linux/fsnotify.h>

#include <linux/fs_struct.h>

#include <linux/pipe_fs_i.h>

#include <linux/oom.h>



#include <asm/uaccess.h>

#include <asm/mmu_context.h>
@@ -759,6 +760,10 @@ static int exec_mmap(struct mm_struct *mm) 
	tsk->mm = mm;

	tsk->active_mm = mm;

	activate_mm(active_mm, mm);

	if (old_mm && tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {

		atomic_dec(&old_mm->oom_disable_count);

		atomic_inc(&tsk->mm->oom_disable_count);

	}

	task_unlock(tsk);

	arch_pick_mmap_layout(mm);

	if (old_mm) {

fs/proc/base.c

+30 −0
Original line number Diff line number Diff line
@@ -1047,6 +1047,21 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf, 
		return -EACCES;

	}



	task_lock(task);

	if (!task->mm) {

		task_unlock(task);

		unlock_task_sighand(task, &flags);

		put_task_struct(task);

		return -EINVAL;

	}



	if (oom_adjust != task->signal->oom_adj) {

		if (oom_adjust == OOM_DISABLE)

			atomic_inc(&task->mm->oom_disable_count);

		if (task->signal->oom_adj == OOM_DISABLE)

			atomic_dec(&task->mm->oom_disable_count);

	}



	/*

	 * Warn that /proc/pid/oom_adj is deprecated, see

	 * Documentation/feature-removal-schedule.txt.
@@ -1065,6 +1080,7 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf, 
	else

		task->signal->oom_score_adj = (oom_adjust * OOM_SCORE_ADJ_MAX) /

								-OOM_DISABLE;

	task_unlock(task);

	unlock_task_sighand(task, &flags);

	put_task_struct(task);
@@ -1133,6 +1149,19 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf, 
		return -EACCES;

	}



	task_lock(task);

	if (!task->mm) {

		task_unlock(task);

		unlock_task_sighand(task, &flags);

		put_task_struct(task);

		return -EINVAL;

	}

	if (oom_score_adj != task->signal->oom_score_adj) {

		if (oom_score_adj == OOM_SCORE_ADJ_MIN)

			atomic_inc(&task->mm->oom_disable_count);

		if (task->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)

			atomic_dec(&task->mm->oom_disable_count);

	}

	task->signal->oom_score_adj = oom_score_adj;

	/*

	 * Scale /proc/pid/oom_adj appropriately ensuring that OOM_DISABLE is
@@ -1143,6 +1172,7 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf, 
	else

		task->signal->oom_adj = (oom_score_adj * OOM_ADJUST_MAX) /

							OOM_SCORE_ADJ_MAX;

	task_unlock(task);

	unlock_task_sighand(task, &flags);

	put_task_struct(task);

	return count;

include/linux/mm_types.h

+2 −0
Original line number Diff line number Diff line
@@ -310,6 +310,8 @@ struct mm_struct { 
#ifdef CONFIG_MMU_NOTIFIER

	struct mmu_notifier_mm *mmu_notifier_mm;

#endif

	/* How many tasks sharing this mm are OOM_DISABLE */

	atomic_t oom_disable_count;

};



/* Future-safe accessor for struct mm_struct's cpu_vm_mask. */

kernel/exit.c

+3 −0
Original line number Diff line number Diff line
@@ -50,6 +50,7 @@ 
#include <linux/perf_event.h>

#include <trace/events/sched.h>

#include <linux/hw_breakpoint.h>

#include <linux/oom.h>



#include <asm/uaccess.h>

#include <asm/unistd.h>
@@ -687,6 +688,8 @@ static void exit_mm(struct task_struct * tsk) 
	enter_lazy_tlb(mm, current);

	/* We don't want this task to be frozen prematurely */

	clear_freeze_flag(tsk);

	if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)

		atomic_dec(&mm->oom_disable_count);

	task_unlock(tsk);

	mm_update_next_owner(mm);

	mmput(mm);

kernel/fork.c

+14 −1
Original line number Diff line number Diff line
@@ -65,6 +65,7 @@ 
#include <linux/perf_event.h>

#include <linux/posix-timers.h>

#include <linux/user-return-notifier.h>

#include <linux/oom.h>



#include <asm/pgtable.h>

#include <asm/pgalloc.h>
@@ -488,6 +489,7 @@ static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p) 
	mm->cached_hole_size = ~0UL;

	mm_init_aio(mm);

	mm_init_owner(mm, p);

	atomic_set(&mm->oom_disable_count, 0);



	if (likely(!mm_alloc_pgd(mm))) {

		mm->def_flags = 0;
@@ -741,6 +743,8 @@ static int copy_mm(unsigned long clone_flags, struct task_struct * tsk) 
	/* Initializing for Swap token stuff */

	mm->token_priority = 0;

	mm->last_interval = 0;

	if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)

		atomic_inc(&mm->oom_disable_count);



	tsk->mm = mm;

	tsk->active_mm = mm;
@@ -1299,8 +1303,13 @@ static struct task_struct *copy_process(unsigned long clone_flags, 
bad_fork_cleanup_namespaces:

	exit_task_namespaces(p);

bad_fork_cleanup_mm:

	if (p->mm)

	if (p->mm) {

		task_lock(p);

		if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)

			atomic_dec(&p->mm->oom_disable_count);

		task_unlock(p);

		mmput(p->mm);

	}

bad_fork_cleanup_signal:

	if (!(clone_flags & CLONE_THREAD))

		free_signal_struct(p->signal);
@@ -1693,6 +1702,10 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags) 
			active_mm = current->active_mm;

			current->mm = new_mm;

			current->active_mm = new_mm;

			if (current->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {

				atomic_dec(&mm->oom_disable_count);

				atomic_inc(&new_mm->oom_disable_count);

			}

			activate_mm(active_mm, new_mm);

			new_mm = mm;

		}