[v9,2/3] cachestat: implement cachestat syscall
Commit Message
There is currently no good way to query the page cache state of large
file sets and directory trees. There is mincore(), but it scales poorly:
the kernel writes out a lot of bitmap data that userspace has to
aggregate, when the user really doesn not care about per-page
information in that case. The user also needs to mmap and unmap each
file as it goes along, which can be quite slow as well.
This patch implements a new syscall that queries cache state of a file
and summarizes the number of cached pages, number of dirty pages, number
of pages marked for writeback, number of (recently) evicted pages, etc.
in a given range. Currently, the syscall is only wired in for x86
architecture.
NAME
cachestat - query the page cache statistics of a file.
SYNOPSIS
#include <sys/mman.h>
struct cachestat {
__u64 nr_cache;
__u64 nr_dirty;
__u64 nr_writeback;
__u64 nr_evicted;
__u64 nr_recently_evicted;
};
int cachestat(unsigned int fd, loff_t off, size_t len,
struct cachestat *cstat, unsigned int flags);
DESCRIPTION
cachestat() queries the number of cached pages, number of dirty
pages, number of pages marked for writeback, number of evicted
pages, number of recently evicted pages, in the bytes range given by
`off` and `len`.
An evicted page is a page that is previously in the page cache but
has been evicted since. A page is recently evicted if its last
eviction was recent enough that its reentry to the cache would
indicate that it is actively being used by the system, and that
there is memory pressure on the system.
These values are returned in a cachestat struct, whose address is
given by the `cstat` argument.
The `off` and `len` arguments must be non-negative integers. If
`len` > 0, the queried range is [`off`, `off` + `len`]. If `len` ==
0, we will query in the range from `off` to the end of the file.
The `flags` argument is unused for now, but is included for future
extensibility. User should pass 0 (i.e no flag specified).
RETURN VALUE
On success, cachestat returns 0. On error, -1 is returned, and errno
is set to indicate the error.
ERRORS
EFAULT cstat points to an invalid address.
EINVAL invalid offset or flags.
EBADF invalid file descriptor.
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
---
arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
include/linux/compat.h | 4 +-
include/linux/fs.h | 3 +
include/linux/syscalls.h | 4 +
include/uapi/asm-generic/unistd.h | 5 +-
include/uapi/linux/mman.h | 9 ++
init/Kconfig | 10 ++
kernel/sys_ni.c | 1 +
mm/filemap.c | 157 +++++++++++++++++++++++++
10 files changed, 193 insertions(+), 2 deletions(-)
Comments
Hi Nhat,
Thank you for the patch! Perhaps something to improve:
[auto build test WARNING on 1440f576022887004f719883acb094e7e0dd4944]
url: https://github.com/intel-lab-lkp/linux/commits/Nhat-Pham/workingset-refactor-LRU-refault-to-expose-refault-recency-check/20230204-030455
base: 1440f576022887004f719883acb094e7e0dd4944
patch link: https://lore.kernel.org/r/20230203190413.2559707-3-nphamcs%40gmail.com
patch subject: [PATCH v9 2/3] cachestat: implement cachestat syscall
config: i386-allnoconfig (https://download.01.org/0day-ci/archive/20230204/202302040546.JHm5vnYB-lkp@intel.com/config)
compiler: gcc-11 (Debian 11.3.0-8) 11.3.0
reproduce (this is a W=1 build):
# https://github.com/intel-lab-lkp/linux/commit/49a57ed71ac2c005231660c85c3f30c4b47d8b7b
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Nhat-Pham/workingset-refactor-LRU-refault-to-expose-refault-recency-check/20230204-030455
git checkout 49a57ed71ac2c005231660c85c3f30c4b47d8b7b
# save the config file
mkdir build_dir && cp config build_dir/.config
make W=1 O=build_dir ARCH=i386 olddefconfig
make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
All warnings (new ones prefixed by >>):
>> mm/filemap.c:4035:6: warning: no previous prototype for 'ksys_cachestat' [-Wmissing-prototypes]
4035 | long ksys_cachestat(unsigned int fd, loff_t off, size_t len,
| ^~~~~~~~~~~~~~
vim +/ksys_cachestat +4035 mm/filemap.c
4033
4034 #ifdef CONFIG_CACHESTAT_SYSCALL
> 4035 long ksys_cachestat(unsigned int fd, loff_t off, size_t len,
4036 struct cachestat __user *cstat, unsigned int flags)
4037 {
4038 struct fd f = fdget(fd);
4039 struct address_space *mapping;
4040 struct cachestat cs;
4041 pgoff_t first_index = off >> PAGE_SHIFT;
4042 pgoff_t last_index =
4043 len == 0 ? ULONG_MAX : (off + len - 1) >> PAGE_SHIFT;
4044
4045 if (!f.file)
4046 return -EBADF;
4047
4048 if (off < 0 || flags != 0) {
4049 fdput(f);
4050 return -EINVAL;
4051 }
4052
4053 memset(&cs, 0, sizeof(struct cachestat));
4054 mapping = f.file->f_mapping;
4055 filemap_cachestat(mapping, first_index, last_index, &cs);
4056 fdput(f);
4057
4058 if (copy_to_user(cstat, &cs, sizeof(struct cachestat)))
4059 return -EFAULT;
4060
4061 return 0;
4062 }
4063
Hi Nhat,
Thank you for the patch! Yet something to improve:
[auto build test ERROR on 1440f576022887004f719883acb094e7e0dd4944]
url: https://github.com/intel-lab-lkp/linux/commits/Nhat-Pham/workingset-refactor-LRU-refault-to-expose-refault-recency-check/20230204-030455
base: 1440f576022887004f719883acb094e7e0dd4944
patch link: https://lore.kernel.org/r/20230203190413.2559707-3-nphamcs%40gmail.com
patch subject: [PATCH v9 2/3] cachestat: implement cachestat syscall
config: alpha-allnoconfig (https://download.01.org/0day-ci/archive/20230204/202302040606.esjgszqH-lkp@intel.com/config)
compiler: alpha-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://github.com/intel-lab-lkp/linux/commit/49a57ed71ac2c005231660c85c3f30c4b47d8b7b
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Nhat-Pham/workingset-refactor-LRU-refault-to-expose-refault-recency-check/20230204-030455
git checkout 49a57ed71ac2c005231660c85c3f30c4b47d8b7b
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=alpha olddefconfig
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=alpha SHELL=/bin/bash
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
All errors (new ones prefixed by >>):
mm/filemap.c:4035:6: warning: no previous prototype for 'ksys_cachestat' [-Wmissing-prototypes]
4035 | long ksys_cachestat(unsigned int fd, loff_t off, size_t len,
| ^~~~~~~~~~~~~~
In file included from mm/filemap.c:25:
>> include/linux/syscalls.h:243:25: error: conflicting types for 'sys_cachestat'; have 'long int(unsigned int, loff_t, size_t, struct cachestat *, unsigned int)' {aka 'long int(unsigned int, long long int, long unsigned int, struct cachestat *, unsigned int)'}
243 | asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
| ^~~
include/linux/syscalls.h:229:9: note: in expansion of macro '__SYSCALL_DEFINEx'
229 | __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
| ^~~~~~~~~~~~~~~~~
include/linux/syscalls.h:222:36: note: in expansion of macro 'SYSCALL_DEFINEx'
222 | #define SYSCALL_DEFINE5(name, ...) SYSCALL_DEFINEx(5, _##name, __VA_ARGS__)
| ^~~~~~~~~~~~~~~
mm/filemap.c:4095:1: note: in expansion of macro 'SYSCALL_DEFINE5'
4095 | SYSCALL_DEFINE5(cachestat, unsigned int, fd, loff_t, off, size_t, len,
| ^~~~~~~~~~~~~~~
include/linux/syscalls.h:1060:17: note: previous declaration of 'sys_cachestat' with type 'long int(unsigned int, long unsigned int, long unsigned int, size_t, struct cachestat *, unsigned int)' {aka 'long int(unsigned int, long unsigned int, long unsigned int, long unsigned int, struct cachestat *, unsigned int)'}
1060 | asmlinkage long sys_cachestat(unsigned int fd, unsigned long off_low,
| ^~~~~~~~~~~~~
vim +243 include/linux/syscalls.h
1bd21c6c21e848 Dominik Brodowski 2018-04-05 232
e145242ea0df6b Dominik Brodowski 2018-04-09 233 /*
e145242ea0df6b Dominik Brodowski 2018-04-09 234 * The asmlinkage stub is aliased to a function named __se_sys_*() which
e145242ea0df6b Dominik Brodowski 2018-04-09 235 * sign-extends 32-bit ints to longs whenever needed. The actual work is
e145242ea0df6b Dominik Brodowski 2018-04-09 236 * done within __do_sys_*().
e145242ea0df6b Dominik Brodowski 2018-04-09 237 */
1bd21c6c21e848 Dominik Brodowski 2018-04-05 238 #ifndef __SYSCALL_DEFINEx
bed1ffca022cc8 Frederic Weisbecker 2009-03-13 239 #define __SYSCALL_DEFINEx(x, name, ...) \
bee20031772af3 Arnd Bergmann 2018-06-19 240 __diag_push(); \
bee20031772af3 Arnd Bergmann 2018-06-19 241 __diag_ignore(GCC, 8, "-Wattribute-alias", \
bee20031772af3 Arnd Bergmann 2018-06-19 242 "Type aliasing is used to sanitize syscall arguments");\
83460ec8dcac14 Andi Kleen 2013-11-12 @243 asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
e145242ea0df6b Dominik Brodowski 2018-04-09 244 __attribute__((alias(__stringify(__se_sys##name)))); \
c9a211951c7c79 Howard McLauchlan 2018-03-21 245 ALLOW_ERROR_INJECTION(sys##name, ERRNO); \
e145242ea0df6b Dominik Brodowski 2018-04-09 246 static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__));\
e145242ea0df6b Dominik Brodowski 2018-04-09 247 asmlinkage long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)); \
e145242ea0df6b Dominik Brodowski 2018-04-09 248 asmlinkage long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
1a94bc34768e46 Heiko Carstens 2009-01-14 249 { \
e145242ea0df6b Dominik Brodowski 2018-04-09 250 long ret = __do_sys##name(__MAP(x,__SC_CAST,__VA_ARGS__));\
07fe6e00f6cca6 Al Viro 2013-01-21 251 __MAP(x,__SC_TEST,__VA_ARGS__); \
2cf0966683430b Al Viro 2013-01-21 252 __PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__)); \
2cf0966683430b Al Viro 2013-01-21 253 return ret; \
1a94bc34768e46 Heiko Carstens 2009-01-14 254 } \
bee20031772af3 Arnd Bergmann 2018-06-19 255 __diag_pop(); \
e145242ea0df6b Dominik Brodowski 2018-04-09 256 static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
1bd21c6c21e848 Dominik Brodowski 2018-04-05 257 #endif /* __SYSCALL_DEFINEx */
1a94bc34768e46 Heiko Carstens 2009-01-14 258
Hi Nhat,
Thank you for the patch! Yet something to improve:
[auto build test ERROR on 1440f576022887004f719883acb094e7e0dd4944]
url: https://github.com/intel-lab-lkp/linux/commits/Nhat-Pham/workingset-refactor-LRU-refault-to-expose-refault-recency-check/20230204-030455
base: 1440f576022887004f719883acb094e7e0dd4944
patch link: https://lore.kernel.org/r/20230203190413.2559707-3-nphamcs%40gmail.com
patch subject: [PATCH v9 2/3] cachestat: implement cachestat syscall
config: arm-allnoconfig (https://download.01.org/0day-ci/archive/20230204/202302040606.Q2Z9z4KL-lkp@intel.com/config)
compiler: arm-linux-gnueabi-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://github.com/intel-lab-lkp/linux/commit/49a57ed71ac2c005231660c85c3f30c4b47d8b7b
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Nhat-Pham/workingset-refactor-LRU-refault-to-expose-refault-recency-check/20230204-030455
git checkout 49a57ed71ac2c005231660c85c3f30c4b47d8b7b
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=arm olddefconfig
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=arm SHELL=/bin/bash
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
All errors (new ones prefixed by >>):
mm/filemap.c:4035:6: warning: no previous prototype for 'ksys_cachestat' [-Wmissing-prototypes]
4035 | long ksys_cachestat(unsigned int fd, loff_t off, size_t len,
| ^~~~~~~~~~~~~~
In file included from mm/filemap.c:25:
>> include/linux/syscalls.h:243:25: error: conflicting types for 'sys_cachestat'; have 'long int(unsigned int, loff_t, size_t, struct cachestat *, unsigned int)' {aka 'long int(unsigned int, long long int, unsigned int, struct cachestat *, unsigned int)'}
243 | asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
| ^~~
include/linux/syscalls.h:229:9: note: in expansion of macro '__SYSCALL_DEFINEx'
229 | __SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
| ^~~~~~~~~~~~~~~~~
include/linux/syscalls.h:222:36: note: in expansion of macro 'SYSCALL_DEFINEx'
222 | #define SYSCALL_DEFINE5(name, ...) SYSCALL_DEFINEx(5, _##name, __VA_ARGS__)
| ^~~~~~~~~~~~~~~
mm/filemap.c:4095:1: note: in expansion of macro 'SYSCALL_DEFINE5'
4095 | SYSCALL_DEFINE5(cachestat, unsigned int, fd, loff_t, off, size_t, len,
| ^~~~~~~~~~~~~~~
include/linux/syscalls.h:1060:17: note: previous declaration of 'sys_cachestat' with type 'long int(unsigned int, long unsigned int, long unsigned int, size_t, struct cachestat *, unsigned int)' {aka 'long int(unsigned int, long unsigned int, long unsigned int, unsigned int, struct cachestat *, unsigned int)'}
1060 | asmlinkage long sys_cachestat(unsigned int fd, unsigned long off_low,
| ^~~~~~~~~~~~~
vim +243 include/linux/syscalls.h
1bd21c6c21e848 Dominik Brodowski 2018-04-05 232
e145242ea0df6b Dominik Brodowski 2018-04-09 233 /*
e145242ea0df6b Dominik Brodowski 2018-04-09 234 * The asmlinkage stub is aliased to a function named __se_sys_*() which
e145242ea0df6b Dominik Brodowski 2018-04-09 235 * sign-extends 32-bit ints to longs whenever needed. The actual work is
e145242ea0df6b Dominik Brodowski 2018-04-09 236 * done within __do_sys_*().
e145242ea0df6b Dominik Brodowski 2018-04-09 237 */
1bd21c6c21e848 Dominik Brodowski 2018-04-05 238 #ifndef __SYSCALL_DEFINEx
bed1ffca022cc8 Frederic Weisbecker 2009-03-13 239 #define __SYSCALL_DEFINEx(x, name, ...) \
bee20031772af3 Arnd Bergmann 2018-06-19 240 __diag_push(); \
bee20031772af3 Arnd Bergmann 2018-06-19 241 __diag_ignore(GCC, 8, "-Wattribute-alias", \
bee20031772af3 Arnd Bergmann 2018-06-19 242 "Type aliasing is used to sanitize syscall arguments");\
83460ec8dcac14 Andi Kleen 2013-11-12 @243 asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \
e145242ea0df6b Dominik Brodowski 2018-04-09 244 __attribute__((alias(__stringify(__se_sys##name)))); \
c9a211951c7c79 Howard McLauchlan 2018-03-21 245 ALLOW_ERROR_INJECTION(sys##name, ERRNO); \
e145242ea0df6b Dominik Brodowski 2018-04-09 246 static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__));\
e145242ea0df6b Dominik Brodowski 2018-04-09 247 asmlinkage long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)); \
e145242ea0df6b Dominik Brodowski 2018-04-09 248 asmlinkage long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
1a94bc34768e46 Heiko Carstens 2009-01-14 249 { \
e145242ea0df6b Dominik Brodowski 2018-04-09 250 long ret = __do_sys##name(__MAP(x,__SC_CAST,__VA_ARGS__));\
07fe6e00f6cca6 Al Viro 2013-01-21 251 __MAP(x,__SC_TEST,__VA_ARGS__); \
2cf0966683430b Al Viro 2013-01-21 252 __PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__)); \
2cf0966683430b Al Viro 2013-01-21 253 return ret; \
1a94bc34768e46 Heiko Carstens 2009-01-14 254 } \
bee20031772af3 Arnd Bergmann 2018-06-19 255 __diag_pop(); \
e145242ea0df6b Dominik Brodowski 2018-04-09 256 static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
1bd21c6c21e848 Dominik Brodowski 2018-04-05 257 #endif /* __SYSCALL_DEFINEx */
1a94bc34768e46 Heiko Carstens 2009-01-14 258
On Fri, Feb 3, 2023, at 20:04, Nhat Pham wrote:
> +SYSCALL_DEFINE5(cachestat, unsigned int, fd, loff_t, off, size_t, len,
> + struct cachestat __user *, cstat, unsigned int, flags)
> +{
> + return ksys_cachestat(fd, off, len, cstat, flags);
> +}
> +
> +#ifdef CONFIG_COMPAT
> +COMPAT_SYSCALL_DEFINE6(cachestat, unsigned int, fd,
> compat_arg_u64_dual(off),
> + size_t, len, struct cachestat __user *, cstat, unsigned int, flags)
> +{
> + return ksys_cachestat(fd, compat_arg_u64_glue(off), len, cstat,
> flags);
> +}
This still looks wrong to me, as this compat definition does not match
the native variant on architectures that require 64-bit arguments to
be passed in aligned register pairs, such as arm, mips or ppc, but
not x86, s390 or riscv.
Arnd
On Sun, Feb 5, 2023 at 1:56 AM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Fri, Feb 3, 2023, at 20:04, Nhat Pham wrote:
>
> > +SYSCALL_DEFINE5(cachestat, unsigned int, fd, loff_t, off, size_t, len,
> > + struct cachestat __user *, cstat, unsigned int, flags)
> > +{
> > + return ksys_cachestat(fd, off, len, cstat, flags);
> > +}
> > +
> > +#ifdef CONFIG_COMPAT
> > +COMPAT_SYSCALL_DEFINE6(cachestat, unsigned int, fd,
> > compat_arg_u64_dual(off),
> > + size_t, len, struct cachestat __user *, cstat, unsigned int, flags)
> > +{
> > + return ksys_cachestat(fd, compat_arg_u64_glue(off), len, cstat,
> > flags);
> > +}
>
> This still looks wrong to me, as this compat definition does not match
> the native variant on architectures that require 64-bit arguments to
> be passed in aligned register pairs, such as arm, mips or ppc, but
> not x86, s390 or riscv.
(looks like I sent the last email in the wrong format - resending this
in plain text to see if the problem persists...)
Oh I see - thanks for pointing that out! And the last bit means this
is a non-issue for x86, s390 or riscv right?
And iirc from the last thread, this is fixable via a simple reordering
of the args in order to properly align the 64-bit arguments, for e.g:
SYSCALL_DEFINE5(cachestat, loff_t, off, unsigned int, fd, size_t, len,
struct cachestat __user *, cstat, unsigned int, flags)
...
COMPAT_SYSCALL_DEFINE6(cachestat, compat_arg_u64_dual(off),
unsigned int, fd, size_t, len, struct cachestat __user *, cstat,
unsigned int, flags)
It looks a bit odd to me that fd is not the first argument, but perhaps this
is an acceptable sacrifice to avoid unused arg and keep the flags...
Let me know what you think about this!
>
> Arnd
On Sun, Feb 12, 2023, at 07:58, Nhat Pham wrote:
> On Sun, Feb 5, 2023 at 4:56 PM Arnd Bergmann <arnd@arndb.de> wrote:
>> On Fri, Feb 3, 2023, at 20:04, Nhat Pham wrote:
>>
>> > +SYSCALL_DEFINE5(cachestat, unsigned int, fd, loff_t, off, size_t, len,
>> > + struct cachestat __user *, cstat, unsigned int, flags)
>> > +{
>> > + return ksys_cachestat(fd, off, len, cstat, flags);
>> > +}
>> > +
>> > +#ifdef CONFIG_COMPAT
>> > +COMPAT_SYSCALL_DEFINE6(cachestat, unsigned int, fd,
>> > compat_arg_u64_dual(off),
>> > + size_t, len, struct cachestat __user *, cstat, unsigned int, flags)
>> > +{
>> > + return ksys_cachestat(fd, compat_arg_u64_glue(off), len, cstat,
>> > flags);
>> > +}
>>
>> This still looks wrong to me, as this compat definition does not match
>> the native variant on architectures that require 64-bit arguments to
>> be passed in aligned register pairs, such as arm, mips or ppc, but
>> not x86, s390 or riscv.
>
> Oh I see - thanks for pointing that out! And the last bit means this
> is a non-issue for x86, s390 or riscv right?
Right. It still requires the separate compat entry point that we
generally try to avoid for new syscalls, but it's probably still
better than passing the offset through a pointer.
> And iirc from the last thread, this is fixable via a simple reordering
> of the args in order to properly align the 64-bit arguments, for e.g:
>
> SYSCALL_DEFINE5(cachestat, loff_t, off, unsigned int, fd, size_t, len,
> struct cachestat __user *, cstat, unsigned int, flags)
>
> ...
>
> COMPAT_SYSCALL_DEFINE6(cachestat, compat_arg_u64_dual(off),
> unsigned int, fd, size_t, len, struct cachestat __user *, cstat,
> unsigned int, flags)
>
>
> It looks a bit odd to me that fd is not the first argument, but perhaps this
> is an acceptable sacrifice to avoid unused arg and keep the flags...
>
> Let me know what you think about this!
Right, this should work. You can also move the offset to the third
or fifth argument in order to keep the fd one first.
I would actually like to change all the syscalls that have loff_t
arguments to have explicit '64-bit' and '32-bit' versions rather
than 'native' and 'compat', to make it more obvious what is going on
even on the architectures that have no 64-bit variant.
That is something to do later though, you should definitely keep
doing this the same way we do for all other syscalls.
Arnd
@@ -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 cachestat sys_cachestat compat_sys_cachestat
@@ -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 cachestat sys_cachestat
#
# Due to a historical design error, certain syscalls are numbered differently
@@ -816,7 +816,9 @@ asmlinkage long compat_sys_sendmsg(int fd, struct compat_msghdr __user *msg,
asmlinkage long compat_sys_recvmsg(int fd, struct compat_msghdr __user *msg,
unsigned int flags);
-/* mm/filemap.c: No generic prototype for readahead */
+/* mm/filemap.c */
+asmlinkage long compat_sys_cachestat(int fd, compat_arg_u64(off),
+ size_t len, struct cachestat __user *cstat, unsigned int flags);
/* security/keys/keyctl.c */
asmlinkage long compat_sys_keyctl(u32 option,
@@ -75,6 +75,7 @@ struct fs_context;
struct fs_parameter_spec;
struct fileattr;
struct iomap_ops;
+struct cachestat;
extern void __init inode_init(void);
extern void __init inode_init_early(void);
@@ -830,6 +831,8 @@ void filemap_invalidate_lock_two(struct address_space *mapping1,
struct address_space *mapping2);
void filemap_invalidate_unlock_two(struct address_space *mapping1,
struct address_space *mapping2);
+void filemap_cachestat(struct address_space *mapping, pgoff_t first_index,
+ pgoff_t last_index, struct cachestat *cs);
/*
@@ -72,6 +72,7 @@ struct open_how;
struct mount_attr;
struct landlock_ruleset_attr;
enum landlock_rule_type;
+struct cachestat;
#include <linux/types.h>
#include <linux/aio_abi.h>
@@ -1056,6 +1057,9 @@ 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_cachestat(unsigned int fd, unsigned long off_low,
+ unsigned long off_high, size_t len, struct cachestat __user *cstat,
+ unsigned int flags);
/*
* Architecture-specific system calls
@@ -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_cachestat 451
+__SC_COMP(__NR_cachestat, sys_cachestat, compat_sys_cachestat)
+
#undef __NR_syscalls
-#define __NR_syscalls 451
+#define __NR_syscalls 452
/*
* 32 bit systems traditionally used different
@@ -4,6 +4,7 @@
#include <asm/mman.h>
#include <asm-generic/hugetlb_encode.h>
+#include <linux/types.h>
#define MREMAP_MAYMOVE 1
#define MREMAP_FIXED 2
@@ -41,4 +42,12 @@
#define MAP_HUGE_2GB HUGETLB_FLAG_ENCODE_2GB
#define MAP_HUGE_16GB HUGETLB_FLAG_ENCODE_16GB
+struct cachestat {
+ __u64 nr_cache;
+ __u64 nr_dirty;
+ __u64 nr_writeback;
+ __u64 nr_evicted;
+ __u64 nr_recently_evicted;
+};
+
#endif /* _UAPI_LINUX_MMAN_H */
@@ -1798,6 +1798,16 @@ config RSEQ
If unsure, say Y.
+config CACHESTAT_SYSCALL
+ bool "Enable cachestat() system call" if EXPERT
+ default y
+ help
+ Enable the cachestat system call, which queries the page cache
+ statistics of a file (number of cached pages, dirty pages,
+ pages marked for writeback, (recently) evicted pages).
+
+ If unsure say Y here.
+
config DEBUG_RSEQ
default n
bool "Enabled debugging of rseq() system call" if EXPERT
@@ -299,6 +299,7 @@ COND_SYSCALL(set_mempolicy);
COND_SYSCALL(migrate_pages);
COND_SYSCALL(move_pages);
COND_SYSCALL(set_mempolicy_home_node);
+COND_SYSCALL(cachestat);
COND_SYSCALL(perf_event_open);
COND_SYSCALL(accept4);
@@ -22,6 +22,7 @@
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/swapops.h>
+#include <linux/syscalls.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/file.h>
@@ -55,6 +56,9 @@
#include <linux/buffer_head.h> /* for try_to_free_buffers */
#include <asm/mman.h>
+#include <uapi/linux/mman.h>
+
+#include "swap.h"
/*
* Shared mappings implemented 30.11.1994. It's not fully working yet,
@@ -3949,3 +3953,156 @@ bool filemap_release_folio(struct folio *folio, gfp_t gfp)
return try_to_free_buffers(folio);
}
EXPORT_SYMBOL(filemap_release_folio);
+
+/**
+ * filemap_cachestat() - compute the page cache statistics of a mapping
+ * @mapping: The mapping to compute the statistics for.
+ * @first_index: The starting page cache index.
+ * @last_index: The final page index (inclusive).
+ * @cs: the cachestat struct to write the result to.
+ *
+ * This will query the page cache statistics of a mapping in the
+ * page range of [first_index, last_index] (inclusive). The statistics
+ * queried include: number of dirty pages, number of pages marked for
+ * writeback, and the number of (recently) evicted pages.
+ */
+void filemap_cachestat(struct address_space *mapping, pgoff_t first_index,
+ pgoff_t last_index, struct cachestat *cs)
+{
+ XA_STATE(xas, &mapping->i_pages, first_index);
+ struct folio *folio;
+
+ rcu_read_lock();
+ xas_for_each(&xas, folio, last_index) {
+ unsigned long nr_pages;
+ pgoff_t folio_first_index, folio_last_index;
+
+ if (xas_retry(&xas, folio))
+ continue;
+
+ nr_pages = folio_nr_pages(folio);
+ folio_first_index = folio_pgoff(folio);
+ folio_last_index = folio_first_index + nr_pages - 1;
+
+ /* Folios might straddle the range boundaries, only count covered subpages */
+ if (folio_first_index < first_index)
+ nr_pages -= first_index - folio_first_index;
+
+ if (folio_last_index > last_index)
+ nr_pages -= folio_last_index - last_index;
+
+ if (xa_is_value(folio)) {
+ /* page is evicted */
+ void *shadow = (void *)folio;
+ bool workingset; /* not used */
+
+ cs->nr_evicted += nr_pages;
+
+#ifdef CONFIG_SWAP /* implies CONFIG_MMU */
+ if (shmem_mapping(mapping)) {
+ /* shmem file - in swap cache */
+ swp_entry_t swp = radix_to_swp_entry(folio);
+
+ shadow = get_shadow_from_swap_cache(swp);
+ }
+#endif
+ if (workingset_test_recent(shadow, true, &workingset))
+ cs->nr_recently_evicted += nr_pages;
+
+ goto resched;
+ }
+
+ /* page is in cache */
+ cs->nr_cache += nr_pages;
+
+ if (folio_test_dirty(folio))
+ cs->nr_dirty += nr_pages;
+
+ if (folio_test_writeback(folio))
+ cs->nr_writeback += nr_pages;
+
+resched:
+ if (need_resched()) {
+ xas_pause(&xas);
+ cond_resched_rcu();
+ }
+ }
+ rcu_read_unlock();
+}
+EXPORT_SYMBOL(filemap_cachestat);
+
+#ifdef CONFIG_CACHESTAT_SYSCALL
+long ksys_cachestat(unsigned int fd, loff_t off, size_t len,
+ struct cachestat __user *cstat, unsigned int flags)
+{
+ struct fd f = fdget(fd);
+ struct address_space *mapping;
+ struct cachestat cs;
+ pgoff_t first_index = off >> PAGE_SHIFT;
+ pgoff_t last_index =
+ len == 0 ? ULONG_MAX : (off + len - 1) >> PAGE_SHIFT;
+
+ if (!f.file)
+ return -EBADF;
+
+ if (off < 0 || flags != 0) {
+ fdput(f);
+ return -EINVAL;
+ }
+
+ memset(&cs, 0, sizeof(struct cachestat));
+ mapping = f.file->f_mapping;
+ filemap_cachestat(mapping, first_index, last_index, &cs);
+ fdput(f);
+
+ if (copy_to_user(cstat, &cs, sizeof(struct cachestat)))
+ return -EFAULT;
+
+ return 0;
+}
+
+/*
+ * The cachestat(5) system call.
+ *
+ * cachestat() returns the page cache statistics of a file in the
+ * bytes range specified by `off` and `len`: number of cached pages,
+ * number of dirty pages, number of pages marked for writeback,
+ * number of evicted pages, and number of recently evicted pages.
+ *
+ * An evicted page is a page that is previously in the page cache
+ * but has been evicted since. A page is recently evicted if its last
+ * eviction was recent enough that its reentry to the cache would
+ * indicate that it is actively being used by the system, and that
+ * there is memory pressure on the system.
+ *
+ * `off` and `len` must be non-negative integers. If `len` > 0,
+ * the queried range is [`off`, `off` + `len`]. If `len` == 0,
+ * we will query in the range from `off` to the end of the file.
+ *
+ * The `flags` argument is unused for now, but is included for future
+ * extensibility. User should pass 0 (i.e no flag specified).
+ *
+ * Because the status of a page can change after cachestat() checks it
+ * but before it returns to the application, the returned values may
+ * contain stale information.
+ *
+ * return values:
+ * zero - success
+ * -EFAULT - cstat points to an illegal address
+ * -EINVAL - invalid arguments
+ * -EBADF - invalid file descriptor
+ */
+SYSCALL_DEFINE5(cachestat, unsigned int, fd, loff_t, off, size_t, len,
+ struct cachestat __user *, cstat, unsigned int, flags)
+{
+ return ksys_cachestat(fd, off, len, cstat, flags);
+}
+
+#ifdef CONFIG_COMPAT
+COMPAT_SYSCALL_DEFINE6(cachestat, unsigned int, fd, compat_arg_u64_dual(off),
+ size_t, len, struct cachestat __user *, cstat, unsigned int, flags)
+{
+ return ksys_cachestat(fd, compat_arg_u64_glue(off), len, cstat, flags);
+}
+#endif
+#endif /* CONFIG_CACHESTAT_SYSCALL */