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

[Mike Rapoport <rppt@kernel.org>]

On Thu, Sep 04, 2025 at 06:57:29PM +0100, 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
> 

...

> +		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);

Shouldn't it fail only for collapse? Other advices don't depend on THP.

> +		}
> +
> +		// 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);
> +	}
> +
> +	return 0;
> +}
> -- 
> 2.50.1
> 

-- 
Sincerely yours,
Mike.