Re: [PATCH] tools/mm: Add madvise tool

[Usama Arif <usamaarif642@gmail.com>]

On 04/09/2025 18:57, kirill@shutemov.name wrote:
> From: Kiryl Shutsemau <kas@kernel.org>
> 
> Add a simple tool that allows to issue an advice on a process or a file.
> 
> It can be useful to experiment with effects of an advice on a workload
> without modifying the workload itself.
> 
> Only supports advices available for process_madvise().
> 
> Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
> ---
>  tools/mm/.gitignore |   4 +-
>  tools/mm/Makefile   |   2 +-
>  tools/mm/madvise.c  | 170 ++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 174 insertions(+), 2 deletions(-)
>  create mode 100644 tools/mm/madvise.c
> 
> diff --git a/tools/mm/.gitignore b/tools/mm/.gitignore
> index 922879f93fc8..b713fcf4a2e0 100644
> --- a/tools/mm/.gitignore
> +++ b/tools/mm/.gitignore
> @@ -1,4 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0-only
> -slabinfo
> +madvise
>  page-types
>  page_owner_sort
> +slabinfo
> +thp_swap_allocator_test
> diff --git a/tools/mm/Makefile b/tools/mm/Makefile
> index f5725b5c23aa..db315a48adcd 100644
> --- a/tools/mm/Makefile
> +++ b/tools/mm/Makefile
> @@ -3,7 +3,7 @@
>  #
>  include ../scripts/Makefile.include
>  
> -BUILD_TARGETS=page-types slabinfo page_owner_sort thp_swap_allocator_test
> +BUILD_TARGETS= madvise page-types page_owner_sort slabinfo thp_swap_allocator_test
>  INSTALL_TARGETS = $(BUILD_TARGETS) thpmaps
>  
>  LIB_DIR = ../lib/api
> diff --git a/tools/mm/madvise.c b/tools/mm/madvise.c
> new file mode 100644
> index 000000000000..038b3e1076ea
> --- /dev/null
> +++ b/tools/mm/madvise.c
> @@ -0,0 +1,170 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define _GNU_SOURCE
> +#include <fcntl.h>
> +#include <limits.h>
> +#include <stdarg.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <sys/mman.h>
> +#include <sys/syscall.h>
> +
> +static void usage(void)
> +{
> +	printf("madvise TARGET ADVICE START END\n\n");
> +	printf("Arguments:\n");
> +	printf("\t<TARGET>\n");
> +	printf("\t\tA process ID or a file to give the advice to.\n\n");
> +	printf("\t\tUse \"./\" prefix if the file name is all digits.\n\n");
> +	printf("\t<ADVICE>\n");
> +	printf("\t\tcold\t\t- Deactivate a given range of pages\n");
> +	printf("\t\tcollapse\t- Collapse pages in a given range into THPs\n");
> +	printf("\t\tpageout\t\t- Reclaim a given range of pages\n");
> +	printf("\t\twillneed\t- The specified data will be accessed in the near future\n");
> +	printf("\n\t\tSee madvise(2) for more details.\n\n");
> +	printf("\t<START>/<END>\n");
> +	printf("\t\tStart and end addressed for the advice. Must be page-aligned.\n\n");
> +	printf("\t\tFor PID case, it is addresses in the target process address space.\n\n");
> +	printf("\t\tFor file case, it is offsets in the file.\n\n");
> +}
> +
> +static void error(const char *fmt, ...)
> +{
> +	if (fmt) {
> +		va_list argp;
> +
> +		va_start(argp, fmt);
> +		vfprintf(stderr, fmt, argp);
> +		va_end(argp);
> +		printf("\n");
> +	}
> +
> +	usage();
> +	exit(-1);
> +}
> +
> +#define PMD_SIZE_FILE_PATH "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size"
> +static unsigned long read_pmd_pagesize(void)
> +{
> +	int fd;
> +	char buf[20];
> +	ssize_t num_read;
> +
> +	fd = open(PMD_SIZE_FILE_PATH, O_RDONLY);
> +	if (fd == -1)
> +		return 0;
> +
> +	num_read = read(fd, buf, 19);
> +	if (num_read < 1) {
> +		close(fd);
> +		return 0;
> +	}
> +	buf[num_read] = '\0';
> +	close(fd);
> +
> +	return strtoul(buf, NULL, 10);
> +}
> +
> +static int pidfd_open(pid_t pid, unsigned int flags)
> +{
> +	return syscall(SYS_pidfd_open, pid, flags);
> +}
> +
> +int main(int argc, const char *argv[])
> +{
> +	unsigned long pid, start, end, page_size;
> +	int advice;
> +	char *err;
> +	int fd;
> +
> +	if (argc != 5)
> +		error(NULL);
> +
> +	pid = strtoul(argv[1], &err, 10);
> +	if (*err || err == argv[1] ||
> +	    pid > INT_MAX || (pid_t)pid <= 0) {
> +		// Not a PID, assume argv[1] is a file name
> +		pid = 0;
> +	}
> +
> +	if (pid) {
> +		fd = pidfd_open(pid, 0);
> +		if (fd < 0)
> +			perror("pidfd_open()"), exit(-1);
> +	} else {
> +		fd = open(argv[1], O_RDWR);
> +		if (fd < 0)
> +			perror("open"), exit(-1);
> +	}
> +
> +	if (!strcmp(argv[2], "cold"))
> +		advice = MADV_COLD;
> +	else if (!strcmp(argv[2], "collapse"))
> +		advice = MADV_COLLAPSE;
> +	else if (!strcmp(argv[2], "pageout"))
> +		advice = MADV_PAGEOUT;
> +	else if (!strcmp(argv[2], "willneed"))
> +		advice = MADV_WILLNEED;
> +	else
> +		error("Unknown advice: %s\n", argv[2]);
> +
> +	page_size = sysconf(_SC_PAGE_SIZE);
> +
> +	start = strtoul(argv[3], &err, 0);
> +	if (*err || err == argv[3])
> +		error("Cannot parse start address\n");
> +	if (start % page_size)
> +		error("Start address is not aligned to page size\n");
> +	end = strtoul(argv[4], &err, 0);
> +	if (*err || err == argv[4])
> +		error("Cannot parse end address\n");
> +	if (end % page_size)
> +		error("End address is not aligned to page size\n");
> +
> +	if (pid) {
> +		struct iovec vec = {
> +			.iov_base = (void *)start,
> +			.iov_len = end - start,
> +		};
> +		ssize_t ret;
> +
> +		ret = process_madvise(fd, &vec, 1, advice, 0);
> +		if (ret < 0)
> +			perror("process_madvise"), exit(-1);
> +
> +		if ((unsigned long)ret != end - start)
> +			printf("Partial advice occurred. Stopped at %#lx\n", start + ret);
> +	} else {
> +		unsigned long addr, hpage_pmd_size;
> +		void *p;
> +		int ret;
> +
> +		hpage_pmd_size = read_pmd_pagesize();
> +		if (!hpage_pmd_size) {
> +			printf("Reading PMD pagesize failed");
> +			exit(-1);
> +		}
> +
> +		// Allocate virtual address space to align the target mmap to PMD size
> +		// Some advices require this.
> +		p = mmap(NULL, end - start + hpage_pmd_size, PROT_NONE,
> +			 MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> +		if (p == MAP_FAILED)
> +			perror("mmap0"), exit(-1);
> +		addr = (unsigned long)p;
> +		addr += hpage_pmd_size - 1;
> +		addr &= ~(hpage_pmd_size - 1);
> +
> +		p = mmap((void *)addr, end - start,
> +			 PROT_READ | PROT_WRITE, MAP_SHARED | MAP_FIXED | MAP_POPULATE, fd, start);
> +		if (p == MAP_FAILED)
> +			perror("mmap"), exit(-1);
> +
> +		ret = madvise(p, end - start, advice);
> +		if (ret)
> +			perror("madvise"), exit(-1);

Would be good to munmap here and check output?

> +	}
> +
> +	return 0;
> +}