Re: [RFC] mm: add new syscall pidfd_set_mempolicy()

There is usecase that System Management Software(SMS) want to give a
memory policy to other processes to make better use of memory.

The information about how to use memory is not known to the app.
Instead, it is known to the userspace daemon(SMS), and that daemon
will decide the memory usage policy based on different factors.

To solve the issue, this patch introduces a new syscall
pidfd_set_mempolicy(2).  it sets the NUMA memory policy of the thread
specified in pidfd.

In current process context there is no locking because only the process
accesses its own memory policy, so task_work is used in
pidfd_set_mempolicy() to update the mempolicy of the process specified
in pidfd, avoid using locks and race conditions.

The API is as follows,

                long pidfd_set_mempolicy(int pidfd, int mode,
                                     const unsigned long __user *nmask,
                                     unsigned long maxnode,
                                     unsigned int flags);

Set's the [pidfd] task's "task/process memory policy". The pidfd argument
is a PID file descriptor (see pidfd_open(2) man page) that specifies the
process to which the mempolicy is to be applied. The flags argument is
reserved for future use; currently, this argument must be specified as 0.
Please see the set_mempolicy(2) man page for more details about
other's arguments.

Suggested-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Zhongkun He <redacted>
---
 .../admin-guide/mm/numa_memory_policy.rst     | 21 ++++-
 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             |  3 +-
 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/mempolicy.h                     | 11 +++
 include/linux/syscalls.h                      |  4 +
 include/uapi/asm-generic/unistd.h             |  5 +-
 kernel/sys_ni.c                               |  1 +
 mm/mempolicy.c                                | 89 +++++++++++++++++++
 24 files changed, 146 insertions(+), 6 deletions(-)

diff --git a/Documentation/admin-guide/mm/numa_memory_policy.rst b/Documentation/admin-guide/mm/numa_memory_policy.rst
index 5a6afecbb0d0..b864dd88b2d2 100644
--- a/Documentation/admin-guide/mm/numa_memory_policy.rst
+++ b/Documentation/admin-guide/mm/numa_memory_policy.rst

@@ -408,9 +408,10 @@ follows:
 Memory Policy APIs
 ==================

-Linux supports 4 system calls for controlling memory policy.  These APIS
-always affect only the calling task, the calling task's address space, or
-some shared object mapped into the calling task's address space.
+Linux supports 5 system calls for controlling memory policy.  The first four
+APIS affect only the calling task, the calling task's address space, or some
+shared object mapped into the calling task's address space. The last one can
+set the mempolicy of task specified in pidfd.

 .. note::
    the headers that define these APIs and the parameter data types for

@@ -473,6 +474,20 @@ closest to which page allocation will come from. Specifying the home node overri
 the default allocation policy to allocate memory close to the local node for an
 executing CPU.

+Set [pidfd Task] Memory Policy::
+
+        long sys_pidfd_set_mempolicy(int pidfd, int mode,
+                                     const unsigned long __user *nmask,
+                                     unsigned long maxnode,
+                                     unsigned int flags);
+
+Set's the [pidfd] task's "task/process memory policy". The pidfd argument is
+a PID file descriptor (see pidfd_open(2) man page) that specifies the process
+to which the mempolicy is to be applied. The flags argument is reserved for
+future use; currently, this argument must be specified as 0. Please see the
+set_mempolicy(2) man page for more details about other's arguments.
+
+

 Memory Policy Command Line Interface
 ====================================

diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index 3515bc4f16a4..d86baa5a6eca 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl

@@ -490,3 +490,4 @@
 558    common  process_mrelease                sys_process_mrelease
 559    common  futex_waitv                     sys_futex_waitv
 560    common  set_mempolicy_home_node         sys_ni_syscall
+561    common  pidfd_set_mempolicy             sys_ni_syscall

diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index ac964612d8b0..a7ccab8aafef 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl

@@ -464,3 +464,4 @@
 448    common  process_mrelease                sys_process_mrelease
 449    common  futex_waitv                     sys_futex_waitv
 450    common  set_mempolicy_home_node         sys_set_mempolicy_home_node
+451    common  pidfd_set_mempolicy             sys_pidfd_set_mempolicy

diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
index 037feba03a51..64a514f90131 100644
--- a/arch/arm64/include/asm/unistd.h
+++ b/arch/arm64/include/asm/unistd.h

@@ -39,7 +39,7 @@
 #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           451
+#define __NR_compat_syscalls           452
 #endif

 #define __ARCH_WANT_SYS_CLONE

diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h
index 604a2053d006..2e178e9152e6 100644
--- a/arch/arm64/include/asm/unistd32.h
+++ b/arch/arm64/include/asm/unistd32.h

@@ -907,7 +907,8 @@ __SYSCALL(__NR_process_mrelease, sys_process_mrelease)
 __SYSCALL(__NR_futex_waitv, sys_futex_waitv)
 #define __NR_set_mempolicy_home_node 450
 __SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node)
-
+#define __NR_pidfd_set_mempolicy 451
+__SYSCALL(__NR_pidfd_set_mempolicy, sys_pidfd_set_mempolicy)
 /*
  * Please add new compat syscalls above this comment and update
  * __NR_compat_syscalls in asm/unistd.h.

diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
index 78b1d03e86e1..4e5bca7a985c 100644
--- a/arch/ia64/kernel/syscalls/syscall.tbl
+++ b/arch/ia64/kernel/syscalls/syscall.tbl

@@ -371,3 +371,4 @@
 448    common  process_mrelease                sys_process_mrelease
 449    common  futex_waitv                     sys_futex_waitv
 450    common  set_mempolicy_home_node         sys_set_mempolicy_home_node
+451    common  pidfd_set_mempolicy             sys_pidfd_set_mempolicy

diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index b1f3940bc298..8e50bf8ec41d 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl

@@ -450,3 +450,4 @@
 448    common  process_mrelease                sys_process_mrelease
 449    common  futex_waitv                     sys_futex_waitv
 450    common  set_mempolicy_home_node         sys_set_mempolicy_home_node
+451    common  pidfd_set_mempolicy             sys_pidfd_set_mempolicy

diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index 820145e47350..f48e32532c5f 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl

@@ -456,3 +456,4 @@
 448    common  process_mrelease                sys_process_mrelease
 449    common  futex_waitv                     sys_futex_waitv
 450    common  set_mempolicy_home_node         sys_set_mempolicy_home_node
+451    common  pidfd_set_mempolicy             sys_pidfd_set_mempolicy

diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
index 253ff994ed2e..58e7c3140f4a 100644
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl

@@ -389,3 +389,4 @@
 448    n32     process_mrelease                sys_process_mrelease
 449    n32     futex_waitv                     sys_futex_waitv
 450    n32     set_mempolicy_home_node         sys_set_mempolicy_home_node
+451    n32     pidfd_set_mempolicy             sys_pidfd_set_mempolicy

diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
index 3f1886ad9d80..70090c3ada16 100644
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl

@@ -365,3 +365,4 @@
 448    n64     process_mrelease                sys_process_mrelease
 449    n64     futex_waitv                     sys_futex_waitv
 450    common  set_mempolicy_home_node         sys_set_mempolicy_home_node
+451    n64     pidfd_set_mempolicy             sys_pidfd_set_mempolicy

diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
index 8f243e35a7b2..b0b0bad64fa0 100644
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl

@@ -438,3 +438,4 @@
 448    o32     process_mrelease                sys_process_mrelease
 449    o32     futex_waitv                     sys_futex_waitv
 450    o32     set_mempolicy_home_node         sys_set_mempolicy_home_node
+451    o32     pidfd_set_mempolicy             sys_pidfd_set_mempolicy

diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
index 8a99c998da9b..4dfd328490ad 100644
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl

@@ -448,3 +448,4 @@
 448    common  process_mrelease                sys_process_mrelease
 449    common  futex_waitv                     sys_futex_waitv
 450    common  set_mempolicy_home_node         sys_set_mempolicy_home_node
+451    common  pidfd_set_mempolicy             sys_pidfd_set_mempolicy

diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index 2600b4237292..20381463b2b5 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl

@@ -530,3 +530,4 @@
 448    common  process_mrelease                sys_process_mrelease
 449    common  futex_waitv                     sys_futex_waitv
 450    nospu   set_mempolicy_home_node         sys_set_mempolicy_home_node
+451    nospu   pidfd_set_mempolicy             sys_pidfd_set_mempolicy

diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index 799147658dee..5e170dca81f6 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl

@@ -453,3 +453,4 @@
 448  common    process_mrelease        sys_process_mrelease            sys_process_mrelease
 449  common    futex_waitv             sys_futex_waitv                 sys_futex_waitv
 450  common    set_mempolicy_home_node sys_set_mempolicy_home_node     sys_set_mempolicy_home_node
+451  common    pidfd_set_mempolicy     sys_pidfd_set_mempolicy         sys_pidfd_set_mempolicy

diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index 2de85c977f54..bd3a24a9b41f 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl

@@ -453,3 +453,4 @@
 448    common  process_mrelease                sys_process_mrelease
 449    common  futex_waitv                     sys_futex_waitv
 450    common  set_mempolicy_home_node         sys_set_mempolicy_home_node
+451    common  pidfd_set_mempolicy             sys_pidfd_set_mempolicy

diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index 4398cc6fb68d..bea2b5c6314b 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl

@@ -496,3 +496,4 @@
 448    common  process_mrelease                sys_process_mrelease
 449    common  futex_waitv                     sys_futex_waitv
 450    common  set_mempolicy_home_node         sys_set_mempolicy_home_node
+451    common  pidfd_set_mempolicy             sys_pidfd_set_mempolicy

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 320480a8db4f..97bc70f5a8f7 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl

@@ -455,3 +455,4 @@
 448    i386    process_mrelease        sys_process_mrelease
 449    i386    futex_waitv             sys_futex_waitv
 450    i386    set_mempolicy_home_node         sys_set_mempolicy_home_node
+451    i386    pidfd_set_mempolicy     sys_pidfd_set_mempolicy

diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index c84d12608cd2..ba6d19dbd8f8 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl

@@ -372,6 +372,7 @@
 448    common  process_mrelease        sys_process_mrelease
 449    common  futex_waitv             sys_futex_waitv
 450    common  set_mempolicy_home_node sys_set_mempolicy_home_node
+451    common  pidfd_set_mempolicy     sys_pidfd_set_mempolicy

 #
 # 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 52c94ab5c205..9f7c563da4fb 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl

@@ -421,3 +421,4 @@
 448    common  process_mrelease                sys_process_mrelease
 449    common  futex_waitv                     sys_futex_waitv
 450    common  set_mempolicy_home_node         sys_set_mempolicy_home_node
+451    common  pidfd_set_mempolicy             sys_pidfd_set_mempolicy

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index 668389b4b53d..f3c522e8eb38 100644
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h

@@ -54,6 +54,17 @@ struct mempolicy {
        } w;
 };

+/*
+ *  The information of mempolicy used by task_work
+ *  to update it dynamically.
+ */
+struct mpol_worker {
+       unsigned short mode;
+       unsigned short flags;
+       nodemask_t nodes;
+       struct rcu_head update_work;
+};
+
 /*
  * Support for managing mempolicy data objects (clone, copy, destroy)
  * The default fast path of a NULL MPOL_DEFAULT policy is always inlined.

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index a34b0f9a9972..e611c088050b 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h

@@ -1056,6 +1056,10 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
 asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
                                            unsigned long home_node,
                                            unsigned long flags);
+asmlinkage long sys_pidfd_set_mempolicy(int pidfd, int mode,
+                                       const unsigned long __user *nmask,
+                                       unsigned long maxnode,
+                                       unsigned int flags);

 /*
  * Architecture-specific system calls

diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 45fa180cc56a..c38013bbf5b0 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h

@@ -886,8 +886,11 @@ __SYSCALL(__NR_futex_waitv, sys_futex_waitv)
 #define __NR_set_mempolicy_home_node 450
 __SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node)

+#define __NR_pidfd_set_mempolicy 451
+__SYSCALL(__NR_pidfd_set_mempolicy, sys_pidfd_set_mempolicy)
+
 #undef __NR_syscalls
-#define __NR_syscalls 451
+#define __NR_syscalls 452

 /*
  * 32 bit systems traditionally used different

diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 860b2dcf3ac4..5053deb888f7 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c

@@ -299,6 +299,7 @@ COND_SYSCALL(set_mempolicy);
 COND_SYSCALL(migrate_pages);
 COND_SYSCALL(move_pages);
 COND_SYSCALL(set_mempolicy_home_node);
+COND_SYSCALL(pidfd_set_mempolicy);

 COND_SYSCALL(perf_event_open);
 COND_SYSCALL(accept4);

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index b73d3248d976..2ce9be1a9dfd 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c

@@ -102,6 +102,7 @@
 #include <linux/mmu_notifier.h>
 #include <linux/printk.h>
 #include <linux/swapops.h>
+#include <linux/task_work.h>

 #include <asm/tlbflush.h>
 #include <asm/tlb.h>

@@ -1572,6 +1573,94 @@ SYSCALL_DEFINE3(set_mempolicy, int, mode, const unsigned long __user *, nmask,
        return kernel_set_mempolicy(mode, nmask, maxnode);
 }

+/*
+ *  In process context there is no locking, so task_work is used to update
+ *  the mempolicy of process specified in pidfd, avoid using locks.
+ */
+static void pidfd_update_mpol(struct callback_head *cb)
+{
+       struct mpol_worker *worker = container_of(cb, struct mpol_worker, update_work);
+
+       do_set_mempolicy(worker->mode, worker->flags, &worker->nodes);
+       kfree(worker);
+}
+
+/* Set the memory policy of the process specified in pidfd. */
+static long do_pidfd_set_mempolicy(int pidfd, int mode, const unsigned long __user *nmask,
+               unsigned long maxnode, unsigned int flags)
+{
+       nodemask_t nodes, task_nodes, tmp;
+       struct mpol_worker *worker;
+       struct task_struct *task;
+       unsigned short mode_flags;
+       int ret, lmode = mode;
+       unsigned int f_flags;
+
+       if (flags)
+               return -EINVAL;
+
+       task = pidfd_get_task(pidfd, &f_flags);
+       if (IS_ERR(task))
+               return PTR_ERR(task);
+       /*
+        * Check if this process has the right to modify the specified
+        * process.
+        */
+       if (!ptrace_may_access(task, PTRACE_MODE_ATTACH_REALCREDS)) {
+               ret = -EPERM;
+               goto out;
+       }
+
+       /*
+        * Require CAP_SYS_NICE for influencing process performance.
+        * User's task is allowed only.
+        */
+       if (!capable(CAP_SYS_NICE) || (task->flags & PF_KTHREAD)) {
+               ret = -EPERM;
+               goto out;
+       }
+
+       ret = get_nodes(&nodes, nmask, maxnode);
+       if (ret)
+               goto out;
+
+       ret = sanitize_mpol_flags(&lmode, &mode_flags);
+       if (ret)
+               goto out;
+
+       task_nodes = cpuset_mems_allowed(task);
+
+       if (mode_flags & MPOL_F_RELATIVE_NODES)
+               mpol_relative_nodemask(&tmp, &nodes, &task_nodes);
+       else
+               nodes_and(tmp, nodes, task_nodes);
+
+       if (nodes_empty(tmp)) {
+               ret = -EINVAL;
+               goto out;
+       }
+       worker = kzalloc(sizeof(struct mpol_worker), GFP_KERNEL | __GFP_NOWARN);
+       if (!worker) {
+               ret = -ENOMEM;
+               goto out;
+       }
+       init_task_work(&worker->update_work, pidfd_update_mpol);
+       worker->flags = mode_flags;
+       worker->mode = lmode;
+       worker->nodes = nodes;
+
+       ret = task_work_add(task, &worker->update_work, TWA_SIGNAL);
+out:
+       put_task_struct(task);
+       return ret;
+}
+
+SYSCALL_DEFINE5(pidfd_set_mempolicy, int, pidfd, int, mode, const unsigned long __user *, nmask,
+               unsigned long, maxnode, unsigned int, flags)
+{
+       return do_pidfd_set_mempolicy(pidfd, mode, nmask, maxnode, flags);
+}
+
 static int kernel_migrate_pages(pid_t pid, unsigned long maxnode,
                                const unsigned long __user *old_nodes,
                                const unsigned long __user *new_nodes)
--

2.25.1