Re: [PATCH 1/1] mm: introduce process_reap system call

Suren Baghdasaryan
2021-06-29T16:15:48Z

On Tue, Jun 29, 2021 at 6:14 AM Christian Brauner
<christian.brauner@ubuntu.com> wrote:
>
> On Wed, Jun 23, 2021 at 12:28:22PM -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_reap system call that reclaims memory of a dying process
> > from the context of the caller. This way the memory in 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.
> >
> > Previously I proposed a number of alternatives to accomplish this:
> > - https://lore.kernel.org/patchwork/patch/1060407 extending
> > pidfd_send_signal to allow memory reaping using oom_reaper thread;
> > - https://lore.kernel.org/patchwork/patch/1338196 extending
> > pidfd_send_signal to reap memory of the target process synchronously from
> > the context of the caller;
> > - https://lore.kernel.org/patchwork/patch/1344419/ to add MADV_DONTNEED
> > support for process_madvise implementing synchronous memory reaping.
> >
> > The end of the last discussion culminated with suggestion to introduce a
> > dedicated system call (https://lore.kernel.org/patchwork/patch/1344418/#1553875)
> > The reasoning was that the new variant of process_madvise
> > a) does not work on an address range
> > b) is destructive
> > c) doesn't share much code at all with the rest of process_madvise
> > From the userspace point of view it was awkward and inconvenient to provide
> > memory range for this operation that operates on the entire address space.
> > Using special flags or address values to specify the entire address space
> > was too hacky.
> >
> > The API is as follows,
> >
> > int process_reap(int pidfd, unsigned int flags);
> >
> > DESCRIPTION
> > The process_reap() system call is used to free the memory of a
> > dying process.
> >
> > The pidfd selects the process referred to by the PID file
> > descriptor.
> > (See pidofd_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_reap() returns 0. On error, -1 is returned
> > and errno is set to indicate the error.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > ---
> > arch/alpha/kernel/syscalls/syscall.tbl | 1 +
> > arch/arm/tools/syscall.tbl | 1 +
> > arch/arm64/include/asm/unistd.h | 2 +-
> > arch/arm64/include/asm/unistd32.h | 2 +
> > arch/ia64/kernel/syscalls/syscall.tbl | 1 +
> > arch/m68k/kernel/syscalls/syscall.tbl | 1 +
> > arch/microblaze/kernel/syscalls/syscall.tbl | 1 +
> > arch/mips/kernel/syscalls/syscall_n32.tbl | 1 +
> > arch/mips/kernel/syscalls/syscall_n64.tbl | 1 +
> > arch/mips/kernel/syscalls/syscall_o32.tbl | 1 +
> > arch/parisc/kernel/syscalls/syscall.tbl | 1 +
> > arch/powerpc/kernel/syscalls/syscall.tbl | 1 +
> > arch/s390/kernel/syscalls/syscall.tbl | 1 +
> > arch/sh/kernel/syscalls/syscall.tbl | 1 +
> > arch/sparc/kernel/syscalls/syscall.tbl | 1 +
> > arch/x86/entry/syscalls/syscall_32.tbl | 1 +
> > arch/x86/entry/syscalls/syscall_64.tbl | 1 +
> > arch/xtensa/kernel/syscalls/syscall.tbl | 1 +
> > include/linux/syscalls.h | 1 +
> > include/uapi/asm-generic/unistd.h | 4 +-
> > kernel/sys_ni.c | 1 +
> > mm/oom_kill.c | 50 +++++++++++++++++++++
> > 22 files changed, 74 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
> > index 3000a2e8ee21..14b9e81d2fc4 100644
> > --- a/arch/alpha/kernel/syscalls/syscall.tbl
> > +++ b/arch/alpha/kernel/syscalls/syscall.tbl
> > @@ -486,3 +486,4 @@
> > 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 common process_reap sys_process_reap
> > diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
> > index 28e03b5fec00..889b78d0f63f 100644
> > --- a/arch/arm/tools/syscall.tbl
> > +++ b/arch/arm/tools/syscall.tbl
> > @@ -460,3 +460,4 @@
> > 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 common process_reap sys_process_reap
> > diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
> > index 727bfc3be99b..fb7a0be2f3d9 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 448
> > #endif
> >
> > #define __ARCH_WANT_SYS_CLONE
> > diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h
> > index 5dab69d2c22b..80593454173e 100644
> > --- a/arch/arm64/include/asm/unistd32.h
> > +++ b/arch/arm64/include/asm/unistd32.h
> > @@ -900,6 +900,8 @@ __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_reap 447
> > +__SYSCALL(__NR_process_reap, sys_process_reap)
> >
> > /*
> > * 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 bb11fe4c875a..6c94feedf086 100644
> > --- a/arch/ia64/kernel/syscalls/syscall.tbl
> > +++ b/arch/ia64/kernel/syscalls/syscall.tbl
> > @@ -367,3 +367,4 @@
> > 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 common process_reap sys_process_reap
> > diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
> > index 79c2d24c89dd..e80a7fa55696 100644
> > --- a/arch/m68k/kernel/syscalls/syscall.tbl
> > +++ b/arch/m68k/kernel/syscalls/syscall.tbl
> > @@ -446,3 +446,4 @@
> > 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 common process_reap sys_process_reap
> > diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
> > index b11395a20c20..511b2bd61fc1 100644
> > --- a/arch/microblaze/kernel/syscalls/syscall.tbl
> > +++ b/arch/microblaze/kernel/syscalls/syscall.tbl
> > @@ -452,3 +452,4 @@
> > 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 common process_reap sys_process_reap
> > diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
> > index 9220909526f9..1775704c6a24 100644
> > --- a/arch/mips/kernel/syscalls/syscall_n32.tbl
> > +++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
> > @@ -385,3 +385,4 @@
> > 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 n32 process_reap sys_process_reap
> > diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
> > index 9cd1c34f31b5..d769daca3f79 100644
> > --- a/arch/mips/kernel/syscalls/syscall_n64.tbl
> > +++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
> > @@ -361,3 +361,4 @@
> > 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 n64 process_reap sys_process_reap
> > diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
> > index d560c467a8c6..1bd2fc056677 100644
> > --- a/arch/mips/kernel/syscalls/syscall_o32.tbl
> > +++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
> > @@ -434,3 +434,4 @@
> > 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 o32 process_reap sys_process_reap
> > diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
> > index aabc37f8cae3..0012561ca557 100644
> > --- a/arch/parisc/kernel/syscalls/syscall.tbl
> > +++ b/arch/parisc/kernel/syscalls/syscall.tbl
> > @@ -444,3 +444,4 @@
> > 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 common process_reap sys_process_reap
> > diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
> > index 8f052ff4058c..89cbcc732b18 100644
> > --- a/arch/powerpc/kernel/syscalls/syscall.tbl
> > +++ b/arch/powerpc/kernel/syscalls/syscall.tbl
> > @@ -526,3 +526,4 @@
> > 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 common process_reap sys_process_reap
> > diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
> > index 0690263df1dd..7ebd4d809b5e 100644
> > --- a/arch/s390/kernel/syscalls/syscall.tbl
> > +++ b/arch/s390/kernel/syscalls/syscall.tbl
> > @@ -449,3 +449,4 @@
> > 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 common process_reap sys_process_reap sys_process_reap
> > diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
> > index 0b91499ebdcf..178fd47b372e 100644
> > --- a/arch/sh/kernel/syscalls/syscall.tbl
> > +++ b/arch/sh/kernel/syscalls/syscall.tbl
> > @@ -449,3 +449,4 @@
> > 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 common process_reap sys_process_reap
> > diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
> > index e34cc30ef22c..faee121b7ae2 100644
> > --- a/arch/sparc/kernel/syscalls/syscall.tbl
> > +++ b/arch/sparc/kernel/syscalls/syscall.tbl
> > @@ -492,3 +492,4 @@
> > 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 common process_reap sys_process_reap
> > diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
> > index 4bbc267fb36b..cbe070de9884 100644
> > --- a/arch/x86/entry/syscalls/syscall_32.tbl
> > +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> > @@ -451,3 +451,4 @@
> > 444 i386 landlock_create_ruleset sys_landlock_create_ruleset
> > 445 i386 landlock_add_rule sys_landlock_add_rule
> > 446 i386 landlock_restrict_self sys_landlock_restrict_self
> > +447 i386 process_reap sys_process_reap
> > diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
> > index ce18119ea0d0..e6765646731b 100644
> > --- a/arch/x86/entry/syscalls/syscall_64.tbl
> > +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> > @@ -368,6 +368,7 @@
> > 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 common process_reap sys_process_reap
> >
> > #
> > # 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 fd2f30227d96..f0e9dbee1a5b 100644
> > --- a/arch/xtensa/kernel/syscalls/syscall.tbl
> > +++ b/arch/xtensa/kernel/syscalls/syscall.tbl
> > @@ -417,3 +417,4 @@
> > 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 common process_reap sys_process_reap
> > diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> > index 050511e8f1f8..b6659e09bf0d 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_reap(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 d2a942086fcb..b3bf57b928af 100644
> > --- a/include/uapi/asm-generic/unistd.h
> > +++ b/include/uapi/asm-generic/unistd.h
> > @@ -871,9 +871,11 @@ __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_reap 447
> > +__SYSCALL(__NR_process_reap, sys_process_reap)
> >
> > #undef __NR_syscalls
> > -#define __NR_syscalls 447
> > +#define __NR_syscalls 448
> >
> > /*
> > * 32 bit systems traditionally used different
> > diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> > index 0ea8128468c3..56eb7c9f8356 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_reap);
> > COND_SYSCALL(remap_file_pages);
> > COND_SYSCALL(mbind);
> > COND_SYSCALL_COMPAT(mbind);
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index eefd3f5fde46..0f85a0442fa5 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 +1142,52 @@ void pagefault_out_of_memory(void)
> > out_of_memory(&oc);
> > mutex_unlock(&oom_lock);
> > }
> > +
> > +SYSCALL_DEFINE2(process_reap, int, pidfd, unsigned int, flags)
>
> Hey Suren,
>
> Wouldn't
> - process_memory_reap()
> - process_reap_memory()
> - process_mreap()
> be better names?

Hi Christian,
I'm open to other names, whichever sounds better. From the list
process_reap_memory() sounds best to me but I'm open to others as
well.

>
> > +{
> > + struct pid *pid;
> > + struct task_struct *task;
> > + struct mm_struct *mm = NULL;
> > + unsigned int f_flags;
> > + long ret = 0;
> > +
> > + if (flags != 0)
> > + 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;
> > + }
>
> You have a similar pattern in process_madvise():
>
> pid = pidfd_get_pid(pidfd, &f_flags);
> if (IS_ERR(pid)) {
> ret = PTR_ERR(pid);
> goto free_iov;
> }
>
> task = get_pid_task(pid, PIDTYPE_PID);
> if (!task) {
> ret = -ESRCH;
> goto put_pid;
> }
>
> I'd suggest you add a tiny helper to kernel/pid.c and call it in both
> places.

Agree. I'll post the new rev next week to give some more time for
reviews of this version.
Thanks!

>
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