| Message ID | 20200302193630.68771-3-minchan@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | introduce memory hinting API for external process | expand |
Hi Minchan,
I love your patch! Yet something to improve:
[auto build test ERROR on arm64/for-next/core]
[also build test ERROR on arm/for-next m68k/for-next powerpc/next s390/features linus/master v5.6-rc4 next-20200302]
[cannot apply to tip/x86/asm hp-parisc/for-next]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]
url: https://github.com/0day-ci/linux/commits/Minchan-Kim/introduce-memory-hinting-API-for-external-process/20200303-044625
base: https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/core
config: arm64-defconfig (attached as .config)
compiler: aarch64-linux-gcc (GCC) 7.5.0
reproduce:
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
GCC_VERSION=7.5.0 make.cross ARCH=arm64
If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>
All errors (new ones prefixed by >>):
aarch64-linux-ld: arch/arm64/kernel/head.o: relocation R_AARCH64_ABS32 against `_kernel_offset_le_lo32' can not be used when making a shared object
aarch64-linux-ld: arch/arm64/kernel/efi-entry.stub.o: relocation R_AARCH64_ABS32 against `__efistub_stext_offset' can not be used when making a shared object
arch/arm64/kernel/head.o: In function `kimage_vaddr':
(.idmap.text+0x0): dangerous relocation: unsupported relocation
arch/arm64/kernel/head.o: In function `__primary_switch':
(.idmap.text+0x378): dangerous relocation: unsupported relocation
(.idmap.text+0x380): dangerous relocation: unsupported relocation
>> arch/arm64/kernel/sys32.o:(.rodata+0xdb8): undefined reference to `__arm64_process_madvise'
---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
On Tue, Mar 03, 2020 at 06:33:03PM +0800, kbuild test robot wrote: > Hi Minchan, > > I love your patch! Yet something to improve: > > [auto build test ERROR on arm64/for-next/core] > [also build test ERROR on arm/for-next m68k/for-next powerpc/next s390/features linus/master v5.6-rc4 next-20200302] > [cannot apply to tip/x86/asm hp-parisc/for-next] > [if your patch is applied to the wrong git tree, please drop us a note to help > improve the system. BTW, we also suggest to use '--base' option to specify the > base tree in git format-patch, please see https://stackoverflow.com/a/37406982] > > url: https://github.com/0day-ci/linux/commits/Minchan-Kim/introduce-memory-hinting-API-for-external-process/20200303-044625 > base: https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/core > config: arm64-defconfig (attached as .config) > compiler: aarch64-linux-gcc (GCC) 7.5.0 > reproduce: > wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross > chmod +x ~/bin/make.cross > # save the attached .config to linux build tree > GCC_VERSION=7.5.0 make.cross ARCH=arm64 > > If you fix the issue, kindly add following tag > Reported-by: kbuild test robot <lkp@intel.com> > > All errors (new ones prefixed by >>): > > aarch64-linux-ld: arch/arm64/kernel/head.o: relocation R_AARCH64_ABS32 against `_kernel_offset_le_lo32' can not be used when making a shared object > aarch64-linux-ld: arch/arm64/kernel/efi-entry.stub.o: relocation R_AARCH64_ABS32 against `__efistub_stext_offset' can not be used when making a shared object > arch/arm64/kernel/head.o: In function `kimage_vaddr': > (.idmap.text+0x0): dangerous relocation: unsupported relocation > arch/arm64/kernel/head.o: In function `__primary_switch': > (.idmap.text+0x378): dangerous relocation: unsupported relocation > (.idmap.text+0x380): dangerous relocation: unsupported relocation > >> arch/arm64/kernel/sys32.o:(.rodata+0xdb8): undefined reference to `__arm64_process_madvise' > > --- > 0-DAY CI Kernel Test Service, Intel Corporation > https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org Thanks. I guess I had a mistake so I hope this patch should fix the issue. From 3cd8bc4dda41d13bcce6fcf6d9252ff684a1929d Mon Sep 17 00:00:00 2001 From: Minchan Kim <minchan@kernel.org> Date: Tue, 3 Mar 2020 06:53:13 -0800 Subject: [PATCH] mm: fix process_madvise build break for arm64 0-day reported build break from process_madvise on ARM64. aarch64-linux-ld: arch/arm64/kernel/head.o: relocation R_AARCH64_ABS32 against `_kernel_offset_le_lo32' can not be used when making a shared object aarch64-linux-ld: arch/arm64/kernel/efi-entry.stub.o: relocation R_AARCH64_ABS32 against `__efistub_stext_offset' can not be used when making a shared object arch/arm64/kernel/head.o: In function `kimage_vaddr': (.idmap.text+0x0): dangerous relocation: unsupported relocation arch/arm64/kernel/head.o: In function `__primary_switch': (.idmap.text+0x378): dangerous relocation: unsupported relocation (.idmap.text+0x380): dangerous relocation: unsupported relocation >> arch/arm64/kernel/sys32.o:(.rodata+0xdb8): undefined reference to `__arm64_process_madvise' This patch should fix it. Reported-by: kbuild test robot <lkp@intel.com> Signed-off-by: Minchan Kim <minchan@kernel.org> --- arch/arm64/include/asm/unistd32.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h index 2a27be7a1f91..a1eec8d879d4 100644 --- a/arch/arm64/include/asm/unistd32.h +++ b/arch/arm64/include/asm/unistd32.h @@ -884,7 +884,7 @@ __SYSCALL(__NR_openat2, sys_openat2) #define __NR_pidfd_getfd 438 __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd) #define __NR_process_madvise 439 -__SYSCALL(__NR_process_madvise, process_madvise) +__SYSCALL(__NR_process_madvise, sys_process_madvise) /* * Please add new compat syscalls above this comment and update
On 3/2/20 8:36 PM, Minchan Kim wrote: > There is usecase that System Management Software(SMS) want to give > a memory hint like MADV_[COLD|PAGEEOUT] to other processes and > in the case of Android, it is the ActivityManagerService. > > It's similar in spirit to madvise(MADV_WONTNEED), but the information You mean MADV_DONTNEED? > required to make the reclaim decision is not known to the app. This seems to be mixing up the differences between MADV_DONTNEED and COLD/PAGEOUT and self-imposed vs external memory hints? > Instead, > it is known to the centralized userspace daemon(ActivityManagerService), > and that daemon must be able to initiate reclaim on its own without > any app involvement. > > To solve the issue, this patch introduces a new syscall process_madvise(2). > It uses pidfd of an external process to give the hint. > > int process_madvise(int pidfd, void *addr, size_t length, int advise, > unsigned long flag); It's more common to call the argument 'flags' not 'flag'? The code seems to call it flags. Also in line with madvise(2), the 'advise' argument should rather be 'advice'. This is more important for the manpage, but let's be consistent. ... > > Reviewed-by: Suren Baghdasaryan <surenb@google.com> > Signed-off-by: Minchan Kim <minchan@kernel.org> For the core parts, Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
On Thu, Mar 05, 2020 at 07:15:10PM +0100, Vlastimil Babka wrote: > On 3/2/20 8:36 PM, Minchan Kim wrote: > > There is usecase that System Management Software(SMS) want to give > > a memory hint like MADV_[COLD|PAGEEOUT] to other processes and > > in the case of Android, it is the ActivityManagerService. > > > > It's similar in spirit to madvise(MADV_WONTNEED), but the information > > You mean MADV_DONTNEED? Mean to DONT_NEED's future version. > > > required to make the reclaim decision is not known to the app. > > This seems to be mixing up the differences between MADV_DONTNEED and > COLD/PAGEOUT and self-imposed vs external memory hints? Sorry, I don't understand what you want here. > > > Instead, > > it is known to the centralized userspace daemon(ActivityManagerService), > > and that daemon must be able to initiate reclaim on its own without > > any app involvement. > > > > To solve the issue, this patch introduces a new syscall process_madvise(2). > > It uses pidfd of an external process to give the hint. > > > > int process_madvise(int pidfd, void *addr, size_t length, int advise, > > unsigned long flag); > > It's more common to call the argument 'flags' not 'flag'? The code seems to call > it flags. Also in line with madvise(2), the 'advise' argument should rather be > 'advice'. This is more important for the manpage, but let's be consistent. Yub, I will send the patch along with your comment in previous patch. > > ... > > > > > Reviewed-by: Suren Baghdasaryan <surenb@google.com> > > Signed-off-by: Minchan Kim <minchan@kernel.org> > > For the core parts, > Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Thanks for the review!
On Tue, Mar 10, 2020 at 03:20:08PM -0700, Minchan Kim wrote: > On Thu, Mar 05, 2020 at 07:15:10PM +0100, Vlastimil Babka wrote: > > On 3/2/20 8:36 PM, Minchan Kim wrote: > > > There is usecase that System Management Software(SMS) want to give > > > a memory hint like MADV_[COLD|PAGEEOUT] to other processes and > > > in the case of Android, it is the ActivityManagerService. > > > > > > It's similar in spirit to madvise(MADV_WONTNEED), but the information > > > > You mean MADV_DONTNEED? > > Mean to DONT_NEED's future version. > > > > > > required to make the reclaim decision is not known to the app. > > > > This seems to be mixing up the differences between MADV_DONTNEED and > > COLD/PAGEOUT and self-imposed vs external memory hints? > > Sorry, I don't understand what you want here. > > > > > > Instead, > > > it is known to the centralized userspace daemon(ActivityManagerService), > > > and that daemon must be able to initiate reclaim on its own without > > > any app involvement. > > > > > > To solve the issue, this patch introduces a new syscall process_madvise(2). > > > It uses pidfd of an external process to give the hint. > > > > > > int process_madvise(int pidfd, void *addr, size_t length, int advise, > > > unsigned long flag); > > > > It's more common to call the argument 'flags' not 'flag'? The code seems to call > > it flags. Also in line with madvise(2), the 'advise' argument should rather be > > 'advice'. This is more important for the manpage, but let's be consistent. > > Yub, I will send the patch along with your comment in previous patch. Only place to use *advice* in kernel is comment in madvise_willneed. Al other places use advise in kernel so I wanted to be more consistent with other kernel sources. For man page, we could use the term "advice", no problem.
On 3/10/20 11:20 PM, Minchan Kim wrote: > On Thu, Mar 05, 2020 at 07:15:10PM +0100, Vlastimil Babka wrote: >> On 3/2/20 8:36 PM, Minchan Kim wrote: >> > There is usecase that System Management Software(SMS) want to give >> > a memory hint like MADV_[COLD|PAGEEOUT] to other processes and >> > in the case of Android, it is the ActivityManagerService. >> > >> > It's similar in spirit to madvise(MADV_WONTNEED), but the information >> >> You mean MADV_DONTNEED? > > Mean to DONT_NEED's future version. What's that exactly? >> >> > required to make the reclaim decision is not known to the app. >> >> This seems to be mixing up the differences between MADV_DONTNEED and >> COLD/PAGEOUT and self-imposed vs external memory hints? > > Sorry, I don't understand what you want here. You say that process_madvise(MADV_[COLD|PAGEEOUT]) is similar to madvise(MADV_WONTNEED) but the difference is that the information required to make the reclaim decision is not known to the app. I see two differences. One is madvise vs process_madvise, which is explained by "reclaim decision is not known to the app." The other is MADV_WONTNEED vs MADV_[COLD|PAGEEOUT], which is... I'm not sure until you say what's "DONT_NEED's future version" :D Anyway I assume this part is from the versions where the new COLD and PAGEOUT flags were introduced together with external memory hinting API?
On Thu, Mar 12, 2020 at 01:40:26PM +0100, Vlastimil Babka wrote: > On 3/10/20 11:20 PM, Minchan Kim wrote: > > On Thu, Mar 05, 2020 at 07:15:10PM +0100, Vlastimil Babka wrote: > >> On 3/2/20 8:36 PM, Minchan Kim wrote: > >> > There is usecase that System Management Software(SMS) want to give > >> > a memory hint like MADV_[COLD|PAGEEOUT] to other processes and > >> > in the case of Android, it is the ActivityManagerService. > >> > > >> > It's similar in spirit to madvise(MADV_WONTNEED), but the information > >> > >> You mean MADV_DONTNEED? > > > > Mean to DONT_NEED's future version. > > What's that exactly? For zapping timing point of view, dontneed acts immediately so it's very strong hint. However, MADV_COLD and MADV_PAGEOUT does lazily depending on the future. For example, the page never discarded if it's touched before the tail of LRU. If other process which shared the page has touched the page, never paging out. > > >> > >> > required to make the reclaim decision is not known to the app. > >> > >> This seems to be mixing up the differences between MADV_DONTNEED and > >> COLD/PAGEOUT and self-imposed vs external memory hints? > > > > Sorry, I don't understand what you want here. > > You say that process_madvise(MADV_[COLD|PAGEEOUT]) is similar to > madvise(MADV_WONTNEED) but the difference is that the information > required to make the reclaim decision is not known to the app. > > I see two differences. One is madvise vs process_madvise, which is explained by > "reclaim decision is not known to the app." > The other is MADV_WONTNEED vs MADV_[COLD|PAGEEOUT], which is... I'm not sure > until you say what's "DONT_NEED's future version" :D > > Anyway I assume this part is from the versions where the new COLD and PAGEOUT > flags were introduced together with external memory hinting API? Exactly. Maybe it would be better to remove the part once we merged the COLD and PAGEOUT now. Thanks for the review, Vlastimil!
On Thu, Mar 12, 2020 at 01:23:39PM -0700, Minchan Kim wrote: > On Thu, Mar 12, 2020 at 01:40:26PM +0100, Vlastimil Babka wrote: > > On 3/10/20 11:20 PM, Minchan Kim wrote: > > > On Thu, Mar 05, 2020 at 07:15:10PM +0100, Vlastimil Babka wrote: > > >> On 3/2/20 8:36 PM, Minchan Kim wrote: > > >> > There is usecase that System Management Software(SMS) want to give > > >> > a memory hint like MADV_[COLD|PAGEEOUT] to other processes and > > >> > in the case of Android, it is the ActivityManagerService. > > >> > > > >> > It's similar in spirit to madvise(MADV_WONTNEED), but the information > > >> > > >> You mean MADV_DONTNEED? > > > > > > Mean to DONT_NEED's future version. > > > > What's that exactly? > > For zapping timing point of view, dontneed acts immediately so it's very > strong hint. However, MADV_COLD and MADV_PAGEOUT does lazily depending > on the future. For example, the page never discarded if it's touched > before the tail of LRU. If other process which shared the page has > touched the page, never paging out. > > > > > >> > > >> > required to make the reclaim decision is not known to the app. > > >> > > >> This seems to be mixing up the differences between MADV_DONTNEED and > > >> COLD/PAGEOUT and self-imposed vs external memory hints? > > > > > > Sorry, I don't understand what you want here. > > > > You say that process_madvise(MADV_[COLD|PAGEEOUT]) is similar to > > madvise(MADV_WONTNEED) but the difference is that the information > > required to make the reclaim decision is not known to the app. > > > > I see two differences. One is madvise vs process_madvise, which is explained by > > "reclaim decision is not known to the app." > > The other is MADV_WONTNEED vs MADV_[COLD|PAGEEOUT], which is... I'm not sure > > until you say what's "DONT_NEED's future version" :D > > > > Anyway I assume this part is from the versions where the new COLD and PAGEOUT > > flags were introduced together with external memory hinting API? > > Exactly. Maybe it would be better to remove the part once we merged the > COLD and PAGEOUT now. > > Thanks for the review, Vlastimil! Hi Andrew, Per Vlastimil's review, I removed unnecessary part and changed syscall argument name "advise and flag" to "advice and flags" in description. Could you replace the description with this one? Code part is same so no need to be changed. Thanks. From fdb29014c84aebcca4737de735993e87d43ebbbf Mon Sep 17 00:00:00 2001 From: Minchan Kim <minchan@kernel.org> Date: Wed, 6 May 2020 13:54:39 +0000 Subject: [PATCH] mm/madvise: introduce process_madvise() syscall: an external memory hinting API There is usecase that System Management Software(SMS) want to give a memory hint like MADV_[COLD|PAGEEOUT] to other processes and in the case of Android, it is the ActivityManagerService. The information required to make the reclaim decision is not known to the app. Instead, it is known to the centralized userspace daemon(ActivityManagerService), and that daemon must be able to initiate reclaim on its own without any app involvement. To solve the issue, this patch introduces a new syscall process_madvise(2). It uses pidfd of an external process to give the hint. int process_madvise(int pidfd, void *addr, size_t length, int advice, unsigned long flags); 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. I think 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 safer for maintenance rather than introducing a buggy syscall but hard to fix it later. Q.1 - Why does any external entity have better knowledge? Quote from Sandeep "For Android, every application (including the special SystemServer) are forked from Zygote. The reason of course is to share as many libraries and classes between the two as possible to benefit from the preloading during boot. After applications start, (almost) all of the APIs end up calling into this SystemServer process over IPC (binder) and back to the application. In a fully running system, the SystemServer monitors every single process periodically to calculate their PSS / RSS and also decides which process is "important" to the user for interactivity. So, because of how these processes start _and_ the fact that the SystemServer is looping to monitor each process, it does tend to *know* which address range of the application is not used / useful. Besides, we can never rely on applications to clean things up themselves. We've had the "hey app1, the system is low on memory, please trim your memory usage down" notifications for a long time[1]. They rely on applications honoring the broadcasts and very few do. So, if we want to avoid the inevitable killing of the application and restarting it, some way to be able to tell the OS about unimportant memory in these applications will be useful. - ssp Q.2 - How to guarantee the race(i.e., object validation) between when giving a hint from an external process and get the hint from the target process? process_madvise operates on the target process's address space as it exists at the instant that process_madvise is called. If the space target process can run between the time the process_madvise process inspects the target process address space and the time that process_madvise is actually called, process_madvise may operate on memory regions that the calling process does not expect. It's the responsibility of the process calling process_madvise to close this race condition. For example, the calling process can suspend the target process with ptrace, SIGSTOP, or the freezer cgroup so that it doesn't have an opportunity to change its own address space before process_madvise is called. Another option is to operate on memory regions that the caller knows a priori will be unchanged in the target process. Yet another option is to accept the race for certain process_madvise calls after reasoning that mistargeting will do no harm. The suggested API itself does not provide synchronization. It also apply other APIs like move_pages, process_vm_write. The race isn't really a problem though. Why is it so wrong to require that callers do their own synchronization in some manner? Nobody objects to write(2) merely because it's possible for two processes to open the same file and clobber each other's writes --- instead, we tell people to use flock or something. Think about mmap. It never guarantees newly allocated address space is still valid when the user tries to access it because other threads could unmap the memory right before. That's where we need synchronization by using other API or design from userside. It shouldn't be part of API itself. If someone needs more fine-grained synchronization rather than process level, there were two ideas suggested - cookie[2] and anon-fd[3]. Both are applicable via using last reserved argument of the API but I don't think it's necessary right now since we have already ways to prevent the race so don't want to add additional complexity with more fine-grained optimization model. To make the API extend, it reserved an unsigned long as last argument so we could support it in future if someone really needs it. Q.3 - Why doesn't ptrace work? Injecting an madvise in the target process using ptrace would not work for us because such injected madvise would have to be executed by the target process, which means that process would have to be runnable and that creates the risk of the abovementioned race and hinting a wrong VMA. Furthermore, we want to act the hint in caller's context, not the callee's, because the callee is usually limited in cpuset/cgroups or even freezed state so they can't act by themselves quick enough, which causes more thrashing/kill. It doesn't work if the target process are ptraced(e.g., strace, debugger, minidump) because a process can have at most one ptracer. [1] https://developer.android.com/topic/performance/memory" [2] process_getinfo for getting the cookie which is updated whenever vma of process address layout are changed - Daniel Colascione - https://lore.kernel.org/lkml/20190520035254.57579-1-minchan@kernel.org/T/#m7694416fd179b2066a2c62b5b139b14e3894e224 [3] anonymous fd which is used for the object(i.e., address range) validation - Michal Hocko - https://lore.kernel.org/lkml/20200120112722.GY18451@dhcp22.suse.cz/ Link: http://lkml.kernel.org/r/20200302193630.68771-3-minchan@kernel.org Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Suren Baghdasaryan <surenb@google.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com> Cc: Brian Geffon <bgeffon@google.com> Cc: Christian Brauner <christian@brauner.io> Cc: Daniel Colascione <dancol@google.com> Cc: Jann Horn <jannh@google.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: John Dias <joaodias@google.com> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Oleksandr Natalenko <oleksandr@redhat.com> Cc: Sandeep Patil <sspatil@google.com> Cc: SeongJae Park <sj38.park@gmail.com> Cc: SeongJae Park <sjpark@amazon.de> Cc: Shakeel Butt <shakeelb@google.com> Cc: Sonny Rao <sonnyrao@google.com> Cc: Tim Murray <timmurray@google.com> Cc: <linux-man@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl index 36d42da7466a..c82952e6fb80 100644 --- a/arch/alpha/kernel/syscalls/syscall.tbl +++ b/arch/alpha/kernel/syscalls/syscall.tbl @@ -477,3 +477,4 @@ # 545 reserved for clone3 547 common openat2 sys_openat2 548 common pidfd_getfd sys_pidfd_getfd +549 common process_madvise sys_process_madvise diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl index 4d1cf74a2caa..54c2719fec46 100644 --- a/arch/arm/tools/syscall.tbl +++ b/arch/arm/tools/syscall.tbl @@ -451,3 +451,4 @@ 435 common clone3 sys_clone3 437 common openat2 sys_openat2 438 common pidfd_getfd sys_pidfd_getfd +439 common process_madvise sys_process_madvise diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h index 1dd22da1c3a9..75f04a1023be 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 439 +#define __NR_compat_syscalls 440 #endif #define __ARCH_WANT_SYS_CLONE diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h index c1c61635f89c..2a27be7a1f91 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_openat2, sys_openat2) #define __NR_pidfd_getfd 438 __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd) +#define __NR_process_madvise 439 +__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 042911e670b8..9524af1c318c 100644 --- a/arch/ia64/kernel/syscalls/syscall.tbl +++ b/arch/ia64/kernel/syscalls/syscall.tbl @@ -358,3 +358,4 @@ # 435 reserved for clone3 437 common openat2 sys_openat2 438 common pidfd_getfd sys_pidfd_getfd +439 common process_madvise sys_process_madvise diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl index f4f49fcb76d0..8197050c097c 100644 --- a/arch/m68k/kernel/syscalls/syscall.tbl +++ b/arch/m68k/kernel/syscalls/syscall.tbl @@ -437,3 +437,4 @@ 435 common clone3 __sys_clone3 437 common openat2 sys_openat2 438 common pidfd_getfd sys_pidfd_getfd +439 common process_madvise sys_process_madvise diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl index 4c67b11f9c9e..c5b6c8afe445 100644 --- a/arch/microblaze/kernel/syscalls/syscall.tbl +++ b/arch/microblaze/kernel/syscalls/syscall.tbl @@ -443,3 +443,4 @@ 435 common clone3 sys_clone3 437 common openat2 sys_openat2 438 common pidfd_getfd sys_pidfd_getfd +439 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 1f9e8ad636cc..8ec8c558aa9c 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 437 n32 openat2 sys_openat2 438 n32 pidfd_getfd sys_pidfd_getfd +439 n32 process_madvise sys_process_madvise diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl index c0b9d802dbf6..0078f891bb92 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 437 n64 openat2 sys_openat2 438 n64 pidfd_getfd sys_pidfd_getfd +439 n64 process_madvise sys_process_madvise diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl index 52a15f5cd130..09c3b5dc6855 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 437 common openat2 sys_openat2 438 common pidfd_getfd sys_pidfd_getfd +439 common process_madvise sys_process_madvise diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl index 35b61bfc1b1a..97eac48c2937 100644 --- a/arch/powerpc/kernel/syscalls/syscall.tbl +++ b/arch/powerpc/kernel/syscalls/syscall.tbl @@ -519,3 +519,4 @@ 435 nospu clone3 ppc_clone3 437 common openat2 sys_openat2 438 common pidfd_getfd sys_pidfd_getfd +439 common process_madvise sys_process_madvise diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl index bd7bd3581a0f..8dc8bfd958ea 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 437 common openat2 sys_openat2 sys_openat2 438 common pidfd_getfd sys_pidfd_getfd sys_pidfd_getfd +439 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 c7a30fcd135f..e69d98040777 100644 --- a/arch/sh/kernel/syscalls/syscall.tbl +++ b/arch/sh/kernel/syscalls/syscall.tbl @@ -440,3 +440,4 @@ # 435 reserved for clone3 437 common openat2 sys_openat2 438 common pidfd_getfd sys_pidfd_getfd +439 common process_madvise sys_process_madvise diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl index f13615ecdecc..6f6e66dd51f9 100644 --- a/arch/sparc/kernel/syscalls/syscall.tbl +++ b/arch/sparc/kernel/syscalls/syscall.tbl @@ -483,3 +483,4 @@ # 435 reserved for clone3 437 common openat2 sys_openat2 438 common pidfd_getfd sys_pidfd_getfd +439 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 c17cb77eb150..1b2184549e27 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 437 i386 openat2 sys_openat2 __ia32_sys_openat2 438 i386 pidfd_getfd sys_pidfd_getfd __ia32_sys_pidfd_getfd +439 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 44d510bc9b78..82d60eb1e00d 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 437 common openat2 __x64_sys_openat2 438 common pidfd_getfd __x64_sys_pidfd_getfd +439 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 85a9ab1bc04d..165cae047770 100644 --- a/arch/xtensa/kernel/syscalls/syscall.tbl +++ b/arch/xtensa/kernel/syscalls/syscall.tbl @@ -408,3 +408,4 @@ 435 common clone3 sys_clone3 437 common openat2 sys_openat2 438 common pidfd_getfd sys_pidfd_getfd +439 common process_madvise sys_process_madvise diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 1815065d52f3..e4cd2c2f8bb4 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -876,6 +876,8 @@ 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 3a3201e4618e..fa289b91410e 100644 --- a/include/uapi/asm-generic/unistd.h +++ b/include/uapi/asm-generic/unistd.h @@ -855,9 +855,11 @@ __SYSCALL(__NR_clone3, sys_clone3) __SYSCALL(__NR_openat2, sys_openat2) #define __NR_pidfd_getfd 438 __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd) +#define __NR_process_madvise 439 +__SYSCALL(__NR_process_madvise, sys_process_madvise) #undef __NR_syscalls -#define __NR_syscalls 439 +#define __NR_syscalls 440 /* * 32 bit systems traditionally used different diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c index 3b69a560a7ac..6c7332776e8e 100644 --- a/kernel/sys_ni.c +++ b/kernel/sys_ni.c @@ -280,6 +280,7 @@ 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 f75c86b6c463..349473fc6683 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> @@ -986,6 +987,18 @@ 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; + } +} + /* * The madvise(2) system call. * @@ -1033,6 +1046,11 @@ madvise_behavior_valid(int behavior) * MADV_DONTDUMP - the application wants to prevent pages in the given range * from being included in its core dump. * MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump. + * MADV_COLD - the application is not expected to use this memory soon, + * deactivate pages in this range so that they can be reclaimed + * easily if memory pressure hanppens. + * MADV_PAGEOUT - the application is not expected to use this memory soon, + * page out the pages in this range immediately. * * return values: * zero - success @@ -1150,3 +1168,49 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior) { return do_madvise(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) +{ + int ret; + struct fd f; + struct pid *pid; + struct task_struct *task; + struct mm_struct *mm; + + if (flags != 0) + return -EINVAL; + + if (!process_madvise_behavior_valid(behavior)) + return -EINVAL; + + f = fdget(pidfd); + if (!f.file) + return -EBADF; + + pid = pidfd_pid(f.file); + if (IS_ERR(pid)) { + ret = PTR_ERR(pid); + goto fdput; + } + + task = get_pid_task(pid, PIDTYPE_PID); + if (!task) { + ret = -ESRCH; + goto fdput; + } + + mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS); + if (IS_ERR_OR_NULL(mm)) { + ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; + goto release_task; + } + + ret = do_madvise(task, mm, start, len_in, behavior); + mmput(mm); +release_task: + put_task_struct(task); +fdput: + fdput(f); + return ret; +}
There is usecase that System Management Software(SMS) want to give a memory hint like MADV_[COLD|PAGEEOUT] to other processes and in the case of Android, it is the ActivityManagerService. It's similar in spirit to madvise(MADV_WONTNEED), but the information required to make the reclaim decision is not known to the app. Instead, it is known to the centralized userspace daemon(ActivityManagerService), and that daemon must be able to initiate reclaim on its own without any app involvement. To solve the issue, this patch introduces a new syscall process_madvise(2). It uses pidfd of an external process 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. I think 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 safer for maintenance rather than introducing a buggy syscall but hard to fix it later. Q.1 - Why does any external entity have better knowledge? Quote from Sandeep "For Android, every application (including the special SystemServer) are forked from Zygote. The reason of course is to share as many libraries and classes between the two as possible to benefit from the preloading during boot. After applications start, (almost) all of the APIs end up calling into this SystemServer process over IPC (binder) and back to the application. In a fully running system, the SystemServer monitors every single process periodically to calculate their PSS / RSS and also decides which process is "important" to the user for interactivity. So, because of how these processes start _and_ the fact that the SystemServer is looping to monitor each process, it does tend to *know* which address range of the application is not used / useful. Besides, we can never rely on applications to clean things up themselves. We've had the "hey app1, the system is low on memory, please trim your memory usage down" notifications for a long time[1]. They rely on applications honoring the broadcasts and very few do. So, if we want to avoid the inevitable killing of the application and restarting it, some way to be able to tell the OS about unimportant memory in these applications will be useful. - ssp Q.2 - How to guarantee the race(i.e., object validation) between when giving a hint from an external process and get the hint from the target process? process_madvise operates on the target process's address space as it exists at the instant that process_madvise is called. If the space target process can run between the time the process_madvise process inspects the target process address space and the time that process_madvise is actually called, process_madvise may operate on memory regions that the calling process does not expect. It's the responsibility of the process calling process_madvise to close this race condition. For example, the calling process can suspend the target process with ptrace, SIGSTOP, or the freezer cgroup so that it doesn't have an opportunity to change its own address space before process_madvise is called. Another option is to operate on memory regions that the caller knows a priori will be unchanged in the target process. Yet another option is to accept the race for certain process_madvise calls after reasoning that mistargeting will do no harm. The suggested API itself does not provide synchronization. It also apply other APIs like move_pages, process_vm_write. The race isn't really a problem though. Why is it so wrong to require that callers do their own synchronization in some manner? Nobody objects to write(2) merely because it's possible for two processes to open the same file and clobber each other's writes --- instead, we tell people to use flock or something. Think about mmap. It never guarantees newly allocated address space is still valid when the user tries to access it because other threads could unmap the memory right before. That's where we need synchronization by using other API or design from userside. It shouldn't be part of API itself. If someone needs more fine-grained synchronization rather than process level, there were two ideas suggested - cookie[2] and anon-fd[3]. Both are applicable via using last reserved argument of the API but I don't think it's necessary right now since we have already ways to prevent the race so don't want to add additional complexity with more fine-grained optimization model. To make the API extend, it reserved an unsigned long as last argument so we could support it in future if someone really needs it. Q.3 - Why doesn't ptrace work? Injecting an madvise in the target process using ptrace would not work for us because such injected madvise would have to be executed by the target process, which means that process would have to be runnable and that creates the risk of the abovementioned race and hinting a wrong VMA. Furthermore, we want to act the hint in caller's context, not calle because calle is usually limited in cpuset/cgroups or even freezed state so they can't act by themselves quick enough, which causes more thrashing/kill. It doesn't work if the target process are ptraced(e.g., strace, debugger, minidump) because a process can have at most one ptracer. [1] https://developer.android.com/topic/performance/memory" [2] process_getinfo for getting the cookie which is updated whenever vma of process address layout are changed - Daniel Colascione - https://lore.kernel.org/lkml/20190520035254.57579-1-minchan@kernel.org/T/#m7694416fd179b2066a2c62b5b139b14e3894e224 [3] anonymous fd which is used for the object(i.e., address range) validation - Michal Hocko - https://lore.kernel.org/lkml/20200120112722.GY18451@dhcp22.suse.cz/ Reviewed-by: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Minchan Kim <minchan@kernel.org> --- 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 | 4 +- kernel/sys_ni.c | 1 + mm/madvise.c | 64 +++++++++++++++++++++ 21 files changed, 88 insertions(+), 2 deletions(-)