In modern systems it's not unusual to have a system component monitoring
memory conditions of the system and tasked with keeping system memory
pressure under control. One way to accomplish that is to kill
non-essential processes to free up memory for more important ones.
Examples of this are Facebook's OOM killer daemon called oomd and
Android's low memory killer daemon called lmkd.
For such system component it's important to be able to free memory
quickly and efficiently. Unfortunately the time process takes to free
up its memory after receiving a SIGKILL might vary based on the state
of the process (uninterruptible sleep), size and OPP level of the core
the process is running. A mechanism to free resources of the target
process in a more predictable way would improve system's ability to
control its memory pressure.
Introduce process_mrelease system call that releases memory of a dying
process from the context of the caller. This way the memory is freed in
a more controllable way with CPU affinity and priority of the caller.
The workload of freeing the memory will also be charged to the caller.
The operation is allowed only on a dying process.
After previous discussions [1, 2, 3] the decision was made [4] to introduce
a dedicated system call to cover this use case.
The API is as follows,
int process_mrelease(int pidfd, unsigned int flags);
DESCRIPTION
The process_mrelease() system call is used to free the memory of
an exiting process.
The pidfd selects the process referred to by the PID file
descriptor.
(See pidfd_open(2) for further information)
The flags argument is reserved for future use; currently, this
argument must be specified as 0.
RETURN VALUE
On success, process_mrelease() returns 0. On error, -1 is
returned and errno is set to indicate the error.
ERRORS
EBADF pidfd is not a valid PID file descriptor.
EAGAIN Failed to release part of the address space.
EINTR The call was interrupted by a signal; see signal(7).
EINVAL flags is not 0.
EINVAL The memory of the task cannot be released because the
process is not exiting, the address space is shared
with another live process or there is a core dump in
progress.
ENOSYS This system call is not supported, for example, without
MMU support built into Linux.
ESRCH The target process does not exist (i.e., it has terminated
and been waited on).
[1] https://lore.kernel.org/lkml/[email protected]/
[2] https://lore.kernel.org/linux-api/[email protected]/
[3] https://lore.kernel.org/linux-api/[email protected]/
[4] https://lore.kernel.org/linux-api/[email protected]/
Signed-off-by: Suren Baghdasaryan <[email protected]>
---
changes in v8:
- Replaced mmget with mmgrab, per Shakeel Butt
- Refactored the code to simplify and fix the task_lock release issue,
per Michal Hocko
mm/oom_kill.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 70 insertions(+)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index c729a4c4a1ac..f8acc26f7300 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -28,6 +28,7 @@
#include <linux/sched/task.h>
#include <linux/sched/debug.h>
#include <linux/swap.h>
+#include <linux/syscalls.h>
#include <linux/timex.h>
#include <linux/jiffies.h>
#include <linux/cpuset.h>
@@ -1141,3 +1142,72 @@ void pagefault_out_of_memory(void)
out_of_memory(&oc);
mutex_unlock(&oom_lock);
}
+
+SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags)
+{
+#ifdef CONFIG_MMU
+ struct mm_struct *mm = NULL;
+ struct task_struct *task;
+ struct task_struct *p;
+ unsigned int f_flags;
+ bool reap = true;
+ struct pid *pid;
+ long ret = 0;
+
+ if (flags)
+ return -EINVAL;
+
+ pid = pidfd_get_pid(pidfd, &f_flags);
+ if (IS_ERR(pid))
+ return PTR_ERR(pid);
+
+ task = get_pid_task(pid, PIDTYPE_PID);
+ if (!task) {
+ ret = -ESRCH;
+ goto put_pid;
+ }
+
+ /*
+ * Make sure to choose a thread which still has a reference to mm
+ * during the group exit
+ */
+ p = find_lock_task_mm(task);
+ if (!p) {
+ ret = -ESRCH;
+ goto put_task;
+ }
+
+ mm = p->mm;
+ mmgrab(mm);
+
+ /* If the work has been done already, just exit with success */
+ if (test_bit(MMF_OOM_SKIP, &mm->flags))
+ reap = false;
+ else if (!task_will_free_mem(p)) {
+ reap = false;
+ ret = -EINVAL;
+ }
+ task_unlock(p);
+
+ if (!reap)
+ goto drop_mm;
+
+ if (mmap_read_lock_killable(mm)) {
+ ret = -EINTR;
+ goto drop_mm;
+ }
+ if (!__oom_reap_task_mm(mm))
+ ret = -EAGAIN;
+ mmap_read_unlock(mm);
+
+drop_mm:
+ mmdrop(mm);
+put_task:
+ put_task_struct(task);
+put_pid:
+ put_pid(pid);
+ return ret;
+#else
+ return -ENOSYS;
+#endif /* CONFIG_MMU */
+}
--
2.32.0.605.g8dce9f2422-goog
Split off from prev patch in the series that implements the syscall.
Signed-off-by: Suren Baghdasaryan <[email protected]>
---
arch/alpha/kernel/syscalls/syscall.tbl | 2 ++
arch/arm/tools/syscall.tbl | 2 ++
arch/arm64/include/asm/unistd.h | 2 +-
arch/arm64/include/asm/unistd32.h | 2 ++
arch/ia64/kernel/syscalls/syscall.tbl | 2 ++
arch/m68k/kernel/syscalls/syscall.tbl | 2 ++
arch/microblaze/kernel/syscalls/syscall.tbl | 2 ++
arch/mips/kernel/syscalls/syscall_n32.tbl | 2 ++
arch/mips/kernel/syscalls/syscall_n64.tbl | 2 ++
arch/mips/kernel/syscalls/syscall_o32.tbl | 2 ++
arch/parisc/kernel/syscalls/syscall.tbl | 2 ++
arch/powerpc/kernel/syscalls/syscall.tbl | 2 ++
arch/s390/kernel/syscalls/syscall.tbl | 2 ++
arch/sh/kernel/syscalls/syscall.tbl | 2 ++
arch/sparc/kernel/syscalls/syscall.tbl | 2 ++
arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
arch/xtensa/kernel/syscalls/syscall.tbl | 2 ++
include/linux/syscalls.h | 1 +
include/uapi/asm-generic/unistd.h | 4 +++-
kernel/sys_ni.c | 1 +
21 files changed, 38 insertions(+), 2 deletions(-)
diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index a17687ed4b51..605645eae04c 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -486,3 +486,5 @@
554 common landlock_create_ruleset sys_landlock_create_ruleset
555 common landlock_add_rule sys_landlock_add_rule
556 common landlock_restrict_self sys_landlock_restrict_self
+# 557 reserved for memfd_secret
+558 common process_mrelease sys_process_mrelease
diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index c5df1179fc5d..2f32eb8beca8 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -460,3 +460,5 @@
444 common landlock_create_ruleset sys_landlock_create_ruleset
445 common landlock_add_rule sys_landlock_add_rule
446 common landlock_restrict_self sys_landlock_restrict_self
+# 447 reserved for memfd_secret
+448 common process_mrelease sys_process_mrelease
diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
index 727bfc3be99b..3cb206aea3db 100644
--- a/arch/arm64/include/asm/unistd.h
+++ b/arch/arm64/include/asm/unistd.h
@@ -38,7 +38,7 @@
#define __ARM_NR_compat_set_tls (__ARM_NR_COMPAT_BASE + 5)
#define __ARM_NR_COMPAT_END (__ARM_NR_COMPAT_BASE + 0x800)
-#define __NR_compat_syscalls 447
+#define __NR_compat_syscalls 449
#endif
#define __ARCH_WANT_SYS_CLONE
diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h
index 99ffcafc736c..0f49cdb180dd 100644
--- a/arch/arm64/include/asm/unistd32.h
+++ b/arch/arm64/include/asm/unistd32.h
@@ -901,6 +901,8 @@ __SYSCALL(__NR_landlock_create_ruleset, sys_landlock_create_ruleset)
__SYSCALL(__NR_landlock_add_rule, sys_landlock_add_rule)
#define __NR_landlock_restrict_self 446
__SYSCALL(__NR_landlock_restrict_self, sys_landlock_restrict_self)
+#define __NR_process_mrelease 448
+__SYSCALL(__NR_process_mrelease, sys_process_mrelease)
/*
* Please add new compat syscalls above this comment and update
diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
index 6d07742c57b8..9bf45f2be966 100644
--- a/arch/ia64/kernel/syscalls/syscall.tbl
+++ b/arch/ia64/kernel/syscalls/syscall.tbl
@@ -367,3 +367,5 @@
444 common landlock_create_ruleset sys_landlock_create_ruleset
445 common landlock_add_rule sys_landlock_add_rule
446 common landlock_restrict_self sys_landlock_restrict_self
+# 447 reserved for memfd_secret
+448 common process_mrelease sys_process_mrelease
diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index 541bc1b3a8f9..f1f98ee6c82d 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -446,3 +446,5 @@
444 common landlock_create_ruleset sys_landlock_create_ruleset
445 common landlock_add_rule sys_landlock_add_rule
446 common landlock_restrict_self sys_landlock_restrict_self
+# 447 reserved for memfd_secret
+448 common process_mrelease sys_process_mrelease
diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index a176faca2927..da49ddd4bb54 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -452,3 +452,5 @@
444 common landlock_create_ruleset sys_landlock_create_ruleset
445 common landlock_add_rule sys_landlock_add_rule
446 common landlock_restrict_self sys_landlock_restrict_self
+# 447 reserved for memfd_secret
+448 common process_mrelease sys_process_mrelease
diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
index c2d2e19abea8..56c8d3cf42ed 100644
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
@@ -385,3 +385,5 @@
444 n32 landlock_create_ruleset sys_landlock_create_ruleset
445 n32 landlock_add_rule sys_landlock_add_rule
446 n32 landlock_restrict_self sys_landlock_restrict_self
+# 447 reserved for memfd_secret
+448 n32 process_mrelease sys_process_mrelease
diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
index ac653d08b1ea..1ca7bc337932 100644
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
@@ -361,3 +361,5 @@
444 n64 landlock_create_ruleset sys_landlock_create_ruleset
445 n64 landlock_add_rule sys_landlock_add_rule
446 n64 landlock_restrict_self sys_landlock_restrict_self
+# 447 reserved for memfd_secret
+448 n64 process_mrelease sys_process_mrelease
diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
index 253f2cd70b6b..fd3a9df60ec2 100644
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
@@ -434,3 +434,5 @@
444 o32 landlock_create_ruleset sys_landlock_create_ruleset
445 o32 landlock_add_rule sys_landlock_add_rule
446 o32 landlock_restrict_self sys_landlock_restrict_self
+# 447 reserved for memfd_secret
+448 o32 process_mrelease sys_process_mrelease
diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
index e26187b9ab87..040df1b7a589 100644
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl
@@ -444,3 +444,5 @@
444 common landlock_create_ruleset sys_landlock_create_ruleset
445 common landlock_add_rule sys_landlock_add_rule
446 common landlock_restrict_self sys_landlock_restrict_self
+# 447 reserved for memfd_secret
+448 common process_mrelease sys_process_mrelease
diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index aef2a290e71a..d8ebd7d37c0f 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -526,3 +526,5 @@
444 common landlock_create_ruleset sys_landlock_create_ruleset
445 common landlock_add_rule sys_landlock_add_rule
446 common landlock_restrict_self sys_landlock_restrict_self
+# 447 reserved for memfd_secret
+448 common process_mrelease sys_process_mrelease
diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index 64d51ab5a8b4..57233ace30cb 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@ -449,3 +449,5 @@
444 common landlock_create_ruleset sys_landlock_create_ruleset sys_landlock_create_ruleset
445 common landlock_add_rule sys_landlock_add_rule sys_landlock_add_rule
446 common landlock_restrict_self sys_landlock_restrict_self sys_landlock_restrict_self
+# 447 reserved for memfd_secret
+448 common process_mrelease sys_process_mrelease sys_process_mrelease
diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index e0a70be77d84..2f6e95eb4690 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@ -449,3 +449,5 @@
444 common landlock_create_ruleset sys_landlock_create_ruleset
445 common landlock_add_rule sys_landlock_add_rule
446 common landlock_restrict_self sys_landlock_restrict_self
+# 447 reserved for memfd_secret
+448 common process_mrelease sys_process_mrelease
diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index 603f5a821502..42fc2906215d 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@ -492,3 +492,5 @@
444 common landlock_create_ruleset sys_landlock_create_ruleset
445 common landlock_add_rule sys_landlock_add_rule
446 common landlock_restrict_self sys_landlock_restrict_self
+# 447 reserved for memfd_secret
+448 common process_mrelease sys_process_mrelease
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index ce763a12311c..661a03bcfbd1 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -452,3 +452,4 @@
445 i386 landlock_add_rule sys_landlock_add_rule
446 i386 landlock_restrict_self sys_landlock_restrict_self
447 i386 memfd_secret sys_memfd_secret
+448 i386 process_mrelease sys_process_mrelease
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index f6b57799c1ea..807b6a1de8e8 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -369,6 +369,7 @@
445 common landlock_add_rule sys_landlock_add_rule
446 common landlock_restrict_self sys_landlock_restrict_self
447 common memfd_secret sys_memfd_secret
+448 common process_mrelease sys_process_mrelease
#
# Due to a historical design error, certain syscalls are numbered differently
diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
index 235d67d6ceb4..f4384951f393 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@ -417,3 +417,5 @@
444 common landlock_create_ruleset sys_landlock_create_ruleset
445 common landlock_add_rule sys_landlock_add_rule
446 common landlock_restrict_self sys_landlock_restrict_self
+# 447 reserved for memfd_secret
+448 common process_mrelease sys_process_mrelease
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 69c9a7010081..00bc170a50f0 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -915,6 +915,7 @@ asmlinkage long sys_mincore(unsigned long start, size_t len,
asmlinkage long sys_madvise(unsigned long start, size_t len, int behavior);
asmlinkage long sys_process_madvise(int pidfd, const struct iovec __user *vec,
size_t vlen, int behavior, unsigned int flags);
+asmlinkage long sys_process_mrelease(int pidfd, unsigned int flags);
asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
unsigned long prot, unsigned long pgoff,
unsigned long flags);
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index a9d6fcd95f42..14c8fe863c6d 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -877,9 +877,11 @@ __SYSCALL(__NR_landlock_restrict_self, sys_landlock_restrict_self)
#define __NR_memfd_secret 447
__SYSCALL(__NR_memfd_secret, sys_memfd_secret)
#endif
+#define __NR_process_mrelease 448
+__SYSCALL(__NR_process_mrelease, sys_process_mrelease)
#undef __NR_syscalls
-#define __NR_syscalls 448
+#define __NR_syscalls 449
/*
* 32 bit systems traditionally used different
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 30971b1dd4a9..18a9c2cde767 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -289,6 +289,7 @@ COND_SYSCALL(munlockall);
COND_SYSCALL(mincore);
COND_SYSCALL(madvise);
COND_SYSCALL(process_madvise);
+COND_SYSCALL(process_mrelease);
COND_SYSCALL(remap_file_pages);
COND_SYSCALL(mbind);
COND_SYSCALL_COMPAT(mbind);
--
2.32.0.605.g8dce9f2422-goog
On Sun, Aug 08, 2021 at 09:08:22AM -0700, Suren Baghdasaryan wrote:
> In modern systems it's not unusual to have a system component monitoring
> memory conditions of the system and tasked with keeping system memory
> pressure under control. One way to accomplish that is to kill
> non-essential processes to free up memory for more important ones.
> Examples of this are Facebook's OOM killer daemon called oomd and
> Android's low memory killer daemon called lmkd.
> For such system component it's important to be able to free memory
> quickly and efficiently. Unfortunately the time process takes to free
> up its memory after receiving a SIGKILL might vary based on the state
> of the process (uninterruptible sleep), size and OPP level of the core
> the process is running. A mechanism to free resources of the target
> process in a more predictable way would improve system's ability to
> control its memory pressure.
> Introduce process_mrelease system call that releases memory of a dying
> process from the context of the caller. This way the memory is freed in
> a more controllable way with CPU affinity and priority of the caller.
> The workload of freeing the memory will also be charged to the caller.
> The operation is allowed only on a dying process.
>
> After previous discussions [1, 2, 3] the decision was made [4] to introduce
> a dedicated system call to cover this use case.
>
> The API is as follows,
>
> int process_mrelease(int pidfd, unsigned int flags);
>
> DESCRIPTION
> The process_mrelease() system call is used to free the memory of
> an exiting process.
>
> The pidfd selects the process referred to by the PID file
> descriptor.
> (See pidfd_open(2) for further information)
>
> The flags argument is reserved for future use; currently, this
> argument must be specified as 0.
>
> RETURN VALUE
> On success, process_mrelease() returns 0. On error, -1 is
> returned and errno is set to indicate the error.
>
> ERRORS
> EBADF pidfd is not a valid PID file descriptor.
>
> EAGAIN Failed to release part of the address space.
>
> EINTR The call was interrupted by a signal; see signal(7).
>
> EINVAL flags is not 0.
>
> EINVAL The memory of the task cannot be released because the
> process is not exiting, the address space is shared
> with another live process or there is a core dump in
> progress.
>
> ENOSYS This system call is not supported, for example, without
> MMU support built into Linux.
>
> ESRCH The target process does not exist (i.e., it has terminated
> and been waited on).
>
> [1] https://lore.kernel.org/lkml/[email protected]/
> [2] https://lore.kernel.org/linux-api/[email protected]/
> [3] https://lore.kernel.org/linux-api/[email protected]/
> [4] https://lore.kernel.org/linux-api/[email protected]/
>
> Link: https://lore.kernel.org/r/[email protected]
> Signed-off-by: Suren Baghdasaryan <[email protected]>
> ---
> changes in v8:
> - Replaced mmget with mmgrab, per Shakeel Butt
> - Refactored the code to simplify and fix the task_lock release issue,
> per Michal Hocko
>
> mm/oom_kill.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 70 insertions(+)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index c729a4c4a1ac..f8acc26f7300 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -28,6 +28,7 @@
> #include <linux/sched/task.h>
> #include <linux/sched/debug.h>
> #include <linux/swap.h>
> +#include <linux/syscalls.h>
> #include <linux/timex.h>
> #include <linux/jiffies.h>
> #include <linux/cpuset.h>
> @@ -1141,3 +1142,72 @@ void pagefault_out_of_memory(void)
> out_of_memory(&oc);
> mutex_unlock(&oom_lock);
> }
> +
> +SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags)
> +{
> +#ifdef CONFIG_MMU
> + struct mm_struct *mm = NULL;
> + struct task_struct *task;
> + struct task_struct *p;
> + unsigned int f_flags;
> + bool reap = true;
> + struct pid *pid;
> + long ret = 0;
> +
> + if (flags)
> + return -EINVAL;
> +
> + pid = pidfd_get_pid(pidfd, &f_flags);
> + if (IS_ERR(pid))
> + return PTR_ERR(pid);
> +
> + task = get_pid_task(pid, PIDTYPE_PID);
Technically, we really want PIDTYPE_TGID here. Currently, a pidfd can't
be created for a thread that isn't a thread-group leader. And while we
do make sure that when a pidfd is created the thread is a thread-group
leader, i.e. has a PIDTYPE_TGID entry in its struct pid we might in the
future not carry this restriction and will allow pidfds to refer to a
single thread. When we do that we need to take a good look at all users
carefully. So I'd prefer if this is changed to
task = get_pid_task(pid, PIDTYPE_TGID);
to clearly express that the assumption is that this is a thread-group
leader.
Otherwise,
Acked-by: Christian Brauner <[email protected]>
On Sun 08-08-21 09:08:22, Suren Baghdasaryan wrote:
> In modern systems it's not unusual to have a system component monitoring
> memory conditions of the system and tasked with keeping system memory
> pressure under control. One way to accomplish that is to kill
> non-essential processes to free up memory for more important ones.
> Examples of this are Facebook's OOM killer daemon called oomd and
> Android's low memory killer daemon called lmkd.
> For such system component it's important to be able to free memory
> quickly and efficiently. Unfortunately the time process takes to free
> up its memory after receiving a SIGKILL might vary based on the state
> of the process (uninterruptible sleep), size and OPP level of the core
> the process is running. A mechanism to free resources of the target
> process in a more predictable way would improve system's ability to
> control its memory pressure.
> Introduce process_mrelease system call that releases memory of a dying
> process from the context of the caller. This way the memory is freed in
> a more controllable way with CPU affinity and priority of the caller.
> The workload of freeing the memory will also be charged to the caller.
> The operation is allowed only on a dying process.
>
> After previous discussions [1, 2, 3] the decision was made [4] to introduce
> a dedicated system call to cover this use case.
>
> The API is as follows,
>
> int process_mrelease(int pidfd, unsigned int flags);
>
> DESCRIPTION
> The process_mrelease() system call is used to free the memory of
> an exiting process.
>
> The pidfd selects the process referred to by the PID file
> descriptor.
> (See pidfd_open(2) for further information)
>
> The flags argument is reserved for future use; currently, this
> argument must be specified as 0.
>
> RETURN VALUE
> On success, process_mrelease() returns 0. On error, -1 is
> returned and errno is set to indicate the error.
>
> ERRORS
> EBADF pidfd is not a valid PID file descriptor.
>
> EAGAIN Failed to release part of the address space.
>
> EINTR The call was interrupted by a signal; see signal(7).
>
> EINVAL flags is not 0.
>
> EINVAL The memory of the task cannot be released because the
> process is not exiting, the address space is shared
> with another live process or there is a core dump in
> progress.
>
> ENOSYS This system call is not supported, for example, without
> MMU support built into Linux.
>
> ESRCH The target process does not exist (i.e., it has terminated
> and been waited on).
>
> [1] https://lore.kernel.org/lkml/[email protected]/
> [2] https://lore.kernel.org/linux-api/[email protected]/
> [3] https://lore.kernel.org/linux-api/[email protected]/
> [4] https://lore.kernel.org/linux-api/[email protected]/
>
> Signed-off-by: Suren Baghdasaryan <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Thanks!
> ---
> changes in v8:
> - Replaced mmget with mmgrab, per Shakeel Butt
> - Refactored the code to simplify and fix the task_lock release issue,
> per Michal Hocko
>
> mm/oom_kill.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 70 insertions(+)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index c729a4c4a1ac..f8acc26f7300 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -28,6 +28,7 @@
> #include <linux/sched/task.h>
> #include <linux/sched/debug.h>
> #include <linux/swap.h>
> +#include <linux/syscalls.h>
> #include <linux/timex.h>
> #include <linux/jiffies.h>
> #include <linux/cpuset.h>
> @@ -1141,3 +1142,72 @@ void pagefault_out_of_memory(void)
> out_of_memory(&oc);
> mutex_unlock(&oom_lock);
> }
> +
> +SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags)
> +{
> +#ifdef CONFIG_MMU
> + struct mm_struct *mm = NULL;
> + struct task_struct *task;
> + struct task_struct *p;
> + unsigned int f_flags;
> + bool reap = true;
> + struct pid *pid;
> + long ret = 0;
> +
> + if (flags)
> + return -EINVAL;
> +
> + pid = pidfd_get_pid(pidfd, &f_flags);
> + if (IS_ERR(pid))
> + return PTR_ERR(pid);
> +
> + task = get_pid_task(pid, PIDTYPE_PID);
> + if (!task) {
> + ret = -ESRCH;
> + goto put_pid;
> + }
> +
> + /*
> + * Make sure to choose a thread which still has a reference to mm
> + * during the group exit
> + */
> + p = find_lock_task_mm(task);
> + if (!p) {
> + ret = -ESRCH;
> + goto put_task;
> + }
> +
> + mm = p->mm;
> + mmgrab(mm);
> +
> + /* If the work has been done already, just exit with success */
> + if (test_bit(MMF_OOM_SKIP, &mm->flags))
> + reap = false;
> + else if (!task_will_free_mem(p)) {
> + reap = false;
> + ret = -EINVAL;
> + }
> + task_unlock(p);
> +
> + if (!reap)
> + goto drop_mm;
> +
> + if (mmap_read_lock_killable(mm)) {
> + ret = -EINTR;
> + goto drop_mm;
> + }
> + if (!__oom_reap_task_mm(mm))
> + ret = -EAGAIN;
> + mmap_read_unlock(mm);
> +
> +drop_mm:
> + mmdrop(mm);
> +put_task:
> + put_task_struct(task);
> +put_pid:
> + put_pid(pid);
> + return ret;
> +#else
> + return -ENOSYS;
> +#endif /* CONFIG_MMU */
> +}
> --
> 2.32.0.605.g8dce9f2422-goog
--
Michal Hocko
SUSE Labs
On Sun, Aug 8, 2021 at 6:23 PM Suren Baghdasaryan <[email protected]> wrote:
> Split off from prev patch in the series that implements the syscall.
>
> Signed-off-by: Suren Baghdasaryan <[email protected]>
> arch/m68k/kernel/syscalls/syscall.tbl | 2 ++
Acked-by: Geert Uytterhoeven <[email protected]>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
On Mon, Aug 9, 2021 at 8:23 AM Shakeel Butt <[email protected]> wrote:
>
> On Sun, Aug 8, 2021 at 9:08 AM Suren Baghdasaryan <[email protected]> wrote:
> >
> > In modern systems it's not unusual to have a system component monitoring
> > memory conditions of the system and tasked with keeping system memory
> > pressure under control. One way to accomplish that is to kill
> > non-essential processes to free up memory for more important ones.
> > Examples of this are Facebook's OOM killer daemon called oomd and
> > Android's low memory killer daemon called lmkd.
> > For such system component it's important to be able to free memory
> > quickly and efficiently. Unfortunately the time process takes to free
> > up its memory after receiving a SIGKILL might vary based on the state
> > of the process (uninterruptible sleep), size and OPP level of the core
> > the process is running. A mechanism to free resources of the target
> > process in a more predictable way would improve system's ability to
> > control its memory pressure.
> > Introduce process_mrelease system call that releases memory of a dying
> > process from the context of the caller. This way the memory is freed in
> > a more controllable way with CPU affinity and priority of the caller.
> > The workload of freeing the memory will also be charged to the caller.
> > The operation is allowed only on a dying process.
> >
> > After previous discussions [1, 2, 3] the decision was made [4] to introduce
> > a dedicated system call to cover this use case.
> >
> > The API is as follows,
> >
> > int process_mrelease(int pidfd, unsigned int flags);
> >
> > DESCRIPTION
> > The process_mrelease() system call is used to free the memory of
> > an exiting process.
> >
> > The pidfd selects the process referred to by the PID file
> > descriptor.
> > (See pidfd_open(2) for further information)
> >
> > The flags argument is reserved for future use; currently, this
> > argument must be specified as 0.
> >
> > RETURN VALUE
> > On success, process_mrelease() returns 0. On error, -1 is
> > returned and errno is set to indicate the error.
> >
> > ERRORS
> > EBADF pidfd is not a valid PID file descriptor.
> >
> > EAGAIN Failed to release part of the address space.
> >
> > EINTR The call was interrupted by a signal; see signal(7).
> >
> > EINVAL flags is not 0.
> >
> > EINVAL The memory of the task cannot be released because the
> > process is not exiting, the address space is shared
> > with another live process or there is a core dump in
> > progress.
> >
> > ENOSYS This system call is not supported, for example, without
> > MMU support built into Linux.
> >
> > ESRCH The target process does not exist (i.e., it has terminated
> > and been waited on).
> >
> > [1] https://lore.kernel.org/lkml/[email protected]/
> > [2] https://lore.kernel.org/linux-api/[email protected]/
> > [3] https://lore.kernel.org/linux-api/[email protected]/
> > [4] https://lore.kernel.org/linux-api/[email protected]/
> >
> > Signed-off-by: Suren Baghdasaryan <[email protected]>
>
> Reviewed-by: Shakeel Butt <[email protected]>
Thanks folks! I'll make the change Christian suggested and will push
the next version carrying Acks along, including the one from David
which I forgot to carry in this one.
On Mon, Aug 9, 2021 at 9:23 AM Suren Baghdasaryan <[email protected]> wrote:
>
> On Mon, Aug 9, 2021 at 8:23 AM Shakeel Butt <[email protected]> wrote:
> >
> > On Sun, Aug 8, 2021 at 9:08 AM Suren Baghdasaryan <[email protected]> wrote:
> > >
> > > In modern systems it's not unusual to have a system component monitoring
> > > memory conditions of the system and tasked with keeping system memory
> > > pressure under control. One way to accomplish that is to kill
> > > non-essential processes to free up memory for more important ones.
> > > Examples of this are Facebook's OOM killer daemon called oomd and
> > > Android's low memory killer daemon called lmkd.
> > > For such system component it's important to be able to free memory
> > > quickly and efficiently. Unfortunately the time process takes to free
> > > up its memory after receiving a SIGKILL might vary based on the state
> > > of the process (uninterruptible sleep), size and OPP level of the core
> > > the process is running. A mechanism to free resources of the target
> > > process in a more predictable way would improve system's ability to
> > > control its memory pressure.
> > > Introduce process_mrelease system call that releases memory of a dying
> > > process from the context of the caller. This way the memory is freed in
> > > a more controllable way with CPU affinity and priority of the caller.
> > > The workload of freeing the memory will also be charged to the caller.
> > > The operation is allowed only on a dying process.
> > >
> > > After previous discussions [1, 2, 3] the decision was made [4] to introduce
> > > a dedicated system call to cover this use case.
> > >
> > > The API is as follows,
> > >
> > > int process_mrelease(int pidfd, unsigned int flags);
> > >
> > > DESCRIPTION
> > > The process_mrelease() system call is used to free the memory of
> > > an exiting process.
> > >
> > > The pidfd selects the process referred to by the PID file
> > > descriptor.
> > > (See pidfd_open(2) for further information)
> > >
> > > The flags argument is reserved for future use; currently, this
> > > argument must be specified as 0.
> > >
> > > RETURN VALUE
> > > On success, process_mrelease() returns 0. On error, -1 is
> > > returned and errno is set to indicate the error.
> > >
> > > ERRORS
> > > EBADF pidfd is not a valid PID file descriptor.
> > >
> > > EAGAIN Failed to release part of the address space.
> > >
> > > EINTR The call was interrupted by a signal; see signal(7).
> > >
> > > EINVAL flags is not 0.
> > >
> > > EINVAL The memory of the task cannot be released because the
> > > process is not exiting, the address space is shared
> > > with another live process or there is a core dump in
> > > progress.
> > >
> > > ENOSYS This system call is not supported, for example, without
> > > MMU support built into Linux.
> > >
> > > ESRCH The target process does not exist (i.e., it has terminated
> > > and been waited on).
> > >
> > > [1] https://lore.kernel.org/lkml/[email protected]/
> > > [2] https://lore.kernel.org/linux-api/[email protected]/
> > > [3] https://lore.kernel.org/linux-api/[email protected]/
> > > [4] https://lore.kernel.org/linux-api/[email protected]/
> > >
> > > Signed-off-by: Suren Baghdasaryan <[email protected]>
> >
> > Reviewed-by: Shakeel Butt <[email protected]>
>
> Thanks folks! I'll make the change Christian suggested and will push
> the next version carrying Acks along, including the one from David
> which I forgot to carry in this one.
v9 posted at: https://lore.kernel.org/linux-mm/[email protected]
On Sun, Aug 8, 2021 at 9:08 AM Suren Baghdasaryan <[email protected]> wrote:
>
> In modern systems it's not unusual to have a system component monitoring
> memory conditions of the system and tasked with keeping system memory
> pressure under control. One way to accomplish that is to kill
> non-essential processes to free up memory for more important ones.
> Examples of this are Facebook's OOM killer daemon called oomd and
> Android's low memory killer daemon called lmkd.
> For such system component it's important to be able to free memory
> quickly and efficiently. Unfortunately the time process takes to free
> up its memory after receiving a SIGKILL might vary based on the state
> of the process (uninterruptible sleep), size and OPP level of the core
> the process is running. A mechanism to free resources of the target
> process in a more predictable way would improve system's ability to
> control its memory pressure.
> Introduce process_mrelease system call that releases memory of a dying
> process from the context of the caller. This way the memory is freed in
> a more controllable way with CPU affinity and priority of the caller.
> The workload of freeing the memory will also be charged to the caller.
> The operation is allowed only on a dying process.
>
> After previous discussions [1, 2, 3] the decision was made [4] to introduce
> a dedicated system call to cover this use case.
>
> The API is as follows,
>
> int process_mrelease(int pidfd, unsigned int flags);
>
> DESCRIPTION
> The process_mrelease() system call is used to free the memory of
> an exiting process.
>
> The pidfd selects the process referred to by the PID file
> descriptor.
> (See pidfd_open(2) for further information)
>
> The flags argument is reserved for future use; currently, this
> argument must be specified as 0.
>
> RETURN VALUE
> On success, process_mrelease() returns 0. On error, -1 is
> returned and errno is set to indicate the error.
>
> ERRORS
> EBADF pidfd is not a valid PID file descriptor.
>
> EAGAIN Failed to release part of the address space.
>
> EINTR The call was interrupted by a signal; see signal(7).
>
> EINVAL flags is not 0.
>
> EINVAL The memory of the task cannot be released because the
> process is not exiting, the address space is shared
> with another live process or there is a core dump in
> progress.
>
> ENOSYS This system call is not supported, for example, without
> MMU support built into Linux.
>
> ESRCH The target process does not exist (i.e., it has terminated
> and been waited on).
>
> [1] https://lore.kernel.org/lkml/[email protected]/
> [2] https://lore.kernel.org/linux-api/[email protected]/
> [3] https://lore.kernel.org/linux-api/[email protected]/
> [4] https://lore.kernel.org/linux-api/[email protected]/
>
> Signed-off-by: Suren Baghdasaryan <[email protected]>
Reviewed-by: Shakeel Butt <[email protected]>