Re: [PATCH 2/4] mm: introduce external memory hinting API

From: Christian Brauner
Date: Mon Jan 13 2020 - 05:43:07 EST

On Mon, Jan 13, 2020 at 11:47:11AM +0300, Kirill Tkhai wrote:
> On 11.01.2020 00:34, Minchan Kim wrote:
> > There are usecases that System Management Software(SMS) want to give
> > a memory hint to other processes because it's not known to the
> > application. In the case of Android, ActivityManagerService daemon
> > manges app's life cycle and that daemon must be able to initiate
> > reclaim on its own without any app involvement.
> >
> > To solve the issue, this patch introduces new syscall process_madvise(2).
> > It uses pidfd of an external processs to give the hint.
> >
> > int process_madvise(int pidfd, void *addr, size_t length, int advise,
> > unsigned long flag);
> >
> > Since it could affect other process's address range, only privileged
> > process(CAP_SYS_PTRACE) or something else(e.g., being the same UID)
> > gives it the right to ptrace the process could use it successfully.
> > The flag argument is reserved for future use if we need to extend the
> > API.
> >
> > Supporting all hints madvise has/will supported/support to process_madvise
> > is rather risky. Because we are not sure all hints make sense from external
> > process and implementation for the hint may rely on the caller being
> > in the current context so it could be error-prone. Thus, I just limited
> > hints as MADV_[COLD|PAGEOUT] in this patch.
> >
> > If someone want to add other hints, we could hear hear the usecase and
> > review it for each hint. It's more safe for maintainace rather than
> > introducing a buggy syscall but hard to fix it later.
> >
> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> > ---
> > 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/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 | 2 +
> > include/uapi/asm-generic/unistd.h | 5 +-
> > kernel/sys_ni.c | 1 +
> > mm/madvise.c | 64 +++++++++++++++++++++
> > 21 files changed, 89 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
> > index e56950f23b49..776c61803315 100644
> > --- a/arch/alpha/kernel/syscalls/syscall.tbl
> > +++ b/arch/alpha/kernel/syscalls/syscall.tbl
> > @@ -477,3 +477,4 @@
> > # 545 reserved for clone3
> > 546 common watch_devices sys_watch_devices
> > 547 common openat2 sys_openat2
> > +548 common process_madvise sys_process_madvise
> > diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
> > index 7fb2f4d59210..a43381542276 100644
> > --- a/arch/arm/tools/syscall.tbl
> > +++ b/arch/arm/tools/syscall.tbl
> > @@ -451,3 +451,4 @@
> > 435 common clone3 sys_clone3
> > 436 common watch_devices sys_watch_devices
> > 437 common openat2 sys_openat2
> > +438 common process_madvise sys_process_madvise
> > diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
> > index 8aa00ccb0b96..b722e47377a5 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 438
> > +#define __NR_compat_syscalls 439
> > #endif
> >
> > #define __ARCH_WANT_SYS_CLONE
> > diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h
> > index 31f0ce25719e..5c82557d408f 100644
> > --- a/arch/arm64/include/asm/unistd32.h
> > +++ b/arch/arm64/include/asm/unistd32.h
> > @@ -883,6 +883,8 @@ __SYSCALL(__NR_clone3, sys_clone3)
> > __SYSCALL(__NR_watch_devices, sys_watch_devices)
> > #define __NR_openat2 437
> > __SYSCALL(__NR_openat2, sys_openat2)
> > +#define __NR_openat2 438
> > +__SYSCALL(__NR_process_madvise, process_madvise)
> >
> > /*
> > * 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 b9aa59931905..c156abc9a298 100644
> > --- a/arch/ia64/kernel/syscalls/syscall.tbl
> > +++ b/arch/ia64/kernel/syscalls/syscall.tbl
> > @@ -358,3 +358,4 @@
> > # 435 reserved for clone3
> > 436 common watch_devices sys_watch_devices
> > 437 common openat2 sys_openat2
> > +438 common process_madvise sys_process_madvise
> > diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
> > index 868c1ef89d35..5b6034b6650f 100644
> > --- a/arch/m68k/kernel/syscalls/syscall.tbl
> > +++ b/arch/m68k/kernel/syscalls/syscall.tbl
> > @@ -437,3 +437,4 @@
> > # 435 reserved for clone3
> > 436 common watch_devices sys_watch_devices
> > 437 common openat2 sys_openat2
> > +438 common process_madvise sys_process_madvise
> > diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
> > index 544b4cef18b3..4bef584af09c 100644
> > --- a/arch/microblaze/kernel/syscalls/syscall.tbl
> > +++ b/arch/microblaze/kernel/syscalls/syscall.tbl
> > @@ -443,3 +443,4 @@
> > 435 common clone3 sys_clone3
> > 436 common watch_devices sys_watch_devices
> > 437 common openat2 sys_openat2
> > +438 common process_madvise sys_process_madvise
> > diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
> > index 05e8aee5dae7..94fbd0fcccce 100644
> > --- a/arch/mips/kernel/syscalls/syscall_n32.tbl
> > +++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
> > @@ -376,3 +376,4 @@
> > 435 n32 clone3 __sys_clone3
> > 436 n32 watch_devices sys_watch_devices
> > 437 n32 openat2 sys_openat2
> > +437 n32 process_madivse sys_process_madvise
>
> 438. And several places below has the same mistake.
>
> > diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
> > index 24d6c01328fb..4e6982c429d5 100644
> > --- a/arch/mips/kernel/syscalls/syscall_n64.tbl
> > +++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
> > @@ -352,3 +352,4 @@
> > 435 n64 clone3 __sys_clone3
> > 436 n64 watch_devices sys_watch_devices
> > 437 n64 openat2 sys_openat2
> > +437 n64 process_madvise sys_process_madvise
> > diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
> > index 4b5f77a4e1a2..3aa990caf9dc 100644
> > --- a/arch/parisc/kernel/syscalls/syscall.tbl
> > +++ b/arch/parisc/kernel/syscalls/syscall.tbl
> > @@ -435,3 +435,4 @@
> > 435 common clone3 sys_clone3_wrapper
> > 436 common watch_devices sys_watch_devices
> > 437 common openat2 sys_openat2
> > +437 common process_madvise sys_process_madvise
> > diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
> > index 9716dc85a517..30e727a23f33 100644
> > --- a/arch/powerpc/kernel/syscalls/syscall.tbl
> > +++ b/arch/powerpc/kernel/syscalls/syscall.tbl
> > @@ -519,3 +519,4 @@
> > 435 nospu clone3 ppc_clone3
> > 436 common watch_devices sys_watch_devices
> > 437 common openat2 sys_openat2
> > +437 common process_madvise sys_process_madvise
> > diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
> > index 7da330f8b03e..75722e5ff496 100644
> > --- a/arch/s390/kernel/syscalls/syscall.tbl
> > +++ b/arch/s390/kernel/syscalls/syscall.tbl
> > @@ -440,3 +440,4 @@
> > 435 common clone3 sys_clone3 sys_clone3
> > 436 common watch_devices sys_watch_devices sys_watch_devices
> > 437 common openat2 sys_openat2 sys_openat2
> > +437 common process_madvise sys_process_madvise sys_process_madvise
> > diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
> > index bb7e68e25337..7d7bc7befad3 100644
> > --- a/arch/sh/kernel/syscalls/syscall.tbl
> > +++ b/arch/sh/kernel/syscalls/syscall.tbl
> > @@ -440,3 +440,4 @@
> > # 435 reserved for clone3
> > 436 common watch_devices sys_watch_devices
> > 437 common openat2 sys_openat2
> > +437 common process_madvise sys_process_madvise
> > diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
> > index 646a1fad7218..581d331ff62f 100644
> > --- a/arch/sparc/kernel/syscalls/syscall.tbl
> > +++ b/arch/sparc/kernel/syscalls/syscall.tbl
> > @@ -483,3 +483,4 @@
> > # 435 reserved for clone3
> > 436 common watch_devices sys_watch_devices
> > 437 common openat2 sys_openat2
> > +437 common process_madvise sys_process_madvise
> > diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
> > index 57c53acee290..76a2c266fe7e 100644
> > --- a/arch/x86/entry/syscalls/syscall_32.tbl
> > +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> > @@ -442,3 +442,4 @@
> > 435 i386 clone3 sys_clone3 __ia32_sys_clone3
> > 436 i386 watch_devices sys_watch_devices __ia32_sys_watch_devices
> > 437 i386 openat2 sys_openat2 __ia32_sys_openat2
> > +438 i386 process_madvise sys_process_madvise __ia32_sys_process_madvise
> > diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
> > index 1dd8d21f6500..b697cd8620cb 100644
> > --- a/arch/x86/entry/syscalls/syscall_64.tbl
> > +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> > @@ -359,6 +359,7 @@
> > 435 common clone3 __x64_sys_clone3/ptregs
> > 436 common watch_devices __x64_sys_watch_devices
> > 437 common openat2 __x64_sys_openat2
> > +438 common process_madvise __x64_sys_process_madvise
> >
> > #
> > # x32-specific system call numbers start at 512 to avoid cache impact
> > diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
> > index 0f48ab7bd75b..2e9813ecfd7d 100644
> > --- a/arch/xtensa/kernel/syscalls/syscall.tbl
> > +++ b/arch/xtensa/kernel/syscalls/syscall.tbl
> > @@ -408,3 +408,4 @@
> > 435 common clone3 sys_clone3
> > 436 common watch_devices sys_watch_devices
> > 437 common openat2 sys_openat2
> > +438 common process_madvise sys_process_madvise
> > diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> > index 433c8c85636e..1b58a11ff49f 100644
> > --- a/include/linux/syscalls.h
> > +++ b/include/linux/syscalls.h
> > @@ -877,6 +877,8 @@ asmlinkage long sys_munlockall(void);
> > asmlinkage long sys_mincore(unsigned long start, size_t len,
> > unsigned char __user * vec);
> > asmlinkage long sys_madvise(unsigned long start, size_t len, int behavior);
> > +asmlinkage long sys_process_madvise(int pidfd, unsigned long start,
> > + size_t len, int behavior, unsigned long 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 33f3856a9c3c..4bcd8d366f38 100644
> > --- a/include/uapi/asm-generic/unistd.h
> > +++ b/include/uapi/asm-generic/unistd.h
> > @@ -856,8 +856,11 @@ __SYSCALL(__NR_watch_devices, sys_watch_devices)
> > #define __NR_openat2 437
> > __SYSCALL(__NR_openat2, sys_openat2)
> >
> > +#define __NR_openat2 438
> > +__SYSCALL(__NR_process_madvise, sys_process_madvise)
> > +
> > #undef __NR_syscalls
> > -#define __NR_syscalls 438
> > +#define __NR_syscalls 439
> >
> > /*
> > * 32 bit systems traditionally used different
> > diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> > index 0e9b275260f8..10ce5eac8b4b 100644
> > --- a/kernel/sys_ni.c
> > +++ b/kernel/sys_ni.c
> > @@ -281,6 +281,7 @@ COND_SYSCALL(mlockall);
> > COND_SYSCALL(munlockall);
> > COND_SYSCALL(mincore);
> > COND_SYSCALL(madvise);
> > +COND_SYSCALL(process_madvise);
> > COND_SYSCALL(remap_file_pages);
> > COND_SYSCALL(mbind);
> > COND_SYSCALL_COMPAT(mbind);
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index 0c901de531e4..e15dfb4df7bf 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -17,6 +17,7 @@
> > #include <linux/falloc.h>
> > #include <linux/fadvise.h>
> > #include <linux/sched.h>
> > +#include <linux/sched/mm.h>
> > #include <linux/ksm.h>
> > #include <linux/fs.h>
> > #include <linux/file.h>
> > @@ -993,6 +994,18 @@ madvise_behavior_valid(int behavior)
> > }
> > }
> >
> > +static bool
> > +process_madvise_behavior_valid(int behavior)
> > +{
> > + switch (behavior) {
> > + case MADV_COLD:
> > + case MADV_PAGEOUT:
> > + return true;
> > + default:
> > + return false;
> > + }
> > +}
> > +
> > /*
> > * madvise_common - request behavior hint to address range of the target process
> > *
> > @@ -1169,3 +1182,54 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
> > {
> > return madvise_common(current, current->mm, start, len_in, behavior);
> > }
> > +
> > +SYSCALL_DEFINE5(process_madvise, int, pidfd, unsigned long, start,
> > + size_t, len_in, int, behavior, unsigned long, flags)
>
> I don't like the interface. The fact we have pidfd does not mean,
> we have to use it for new syscalls always. A user may want to set
> madvise for specific pid from console and pass pid as argument.
> pidfd would be an overkill in this case.
> We usually call "kill -9 pid" from console. Why shouldn't process_madvise()
> allow this?
>
> I suggent to extend first argument to work with both pid and pidfd.
> Look at what we have for waitid(idtype, id_t id, ...) for example:
>
> idtype == P_PID
> Wait for the child whose process ID matches id.
>
> idtype == P_PIDFD (since Linux 5.4)
> Wait for the child referred to by the PID file descriptor specified in id. (See pidfd_open(2) for further information on
> PID file descriptors.)
>
> We may use @flags argument for this.

Sorry for chiming in just a comment. Overall, I don't particularly care
how or if you integrate pidfd here. One thing I would like to point out
is that we're working on a patch to place new features under pidfd
specific flags. This e.g. means a pidfd would be only be able to be used
for madvise operations (or getfd operations) if it was created with that
specific flag set making it easier to share them with other processes.
So if you integrate them here I would be quite thankful if you target
the patchset for the v5.7 merge window, not for v5.6.

Thanks!
Christian