linux-kernel - Re: [PATCH v5 05/14] perf bench mem: Switch from zalloc() to mmap()

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Message-ID: <aHa1kNCmugRYDuIM@google.com>
Date: Tue, 15 Jul 2025 13:09:52 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Ankur Arora <ankur.a.arora@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
	akpm@...ux-foundation.org, david@...hat.com, bp@...en8.de,
	dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
	mjguzik@...il.com, luto@...nel.org, peterz@...radead.org,
	acme@...nel.org, tglx@...utronix.de, willy@...radead.org,
	raghavendra.kt@....com, boris.ostrovsky@...cle.com,
	konrad.wilk@...cle.com
Subject: Re: [PATCH v5 05/14] perf bench mem: Switch from zalloc() to mmap()

On Wed, Jul 09, 2025 at 05:59:17PM -0700, Ankur Arora wrote:
> Using mmap() ensures that the buffer is always aligned at a fixed
> boundary. Switch to that to remove one source of variability.
> 
> Since we always want to read/write from the the allocated buffers map
> with pagetables pre-populated.
> 
> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>

Reviewed-by: Namhyung Kim <namhyung@...nel.org>

Thanks,
Namhyung

> ---
>  tools/perf/bench/mem-functions.c | 27 ++++++++++++++++++++++-----
>  1 file changed, 22 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
> index 06d3ee6f5d69..914f9048d982 100644
> --- a/tools/perf/bench/mem-functions.c
> +++ b/tools/perf/bench/mem-functions.c
> @@ -22,9 +22,9 @@
>  #include <string.h>
>  #include <unistd.h>
>  #include <sys/time.h>
> +#include <sys/mman.h>
>  #include <errno.h>
>  #include <linux/time64.h>
> -#include <linux/zalloc.h>
>  
>  #define K 1024
>  
> @@ -285,16 +285,33 @@ static int do_memcpy(const struct function *r, struct bench_params *p,
>  	return 0;
>  }
>  
> +static void *bench_mmap(size_t size, bool populate)
> +{
> +	void *p;
> +	int extra = populate ? MAP_POPULATE : 0;
> +
> +	p = mmap(NULL, size, PROT_READ|PROT_WRITE,
> +		 extra | MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
> +
> +	return p == MAP_FAILED ? NULL : p;
> +}
> +
> +static void bench_munmap(void *p, size_t size)
> +{
> +	if (p)
> +		munmap(p, size);
> +}
> +
>  static bool mem_alloc(struct bench_mem_info *info, struct bench_params *p,
>  		      void **src, void **dst)
>  {
>  	bool failed;
>  
> -	*dst = zalloc(p->size);
> +	*dst = bench_mmap(p->size, true);
>  	failed = *dst == NULL;
>  
>  	if (info->alloc_src) {
> -		*src = zalloc(p->size);
> +		*src = bench_mmap(p->size, true);
>  		failed = failed || *src == NULL;
>  	}
>  
> @@ -305,8 +322,8 @@ static void mem_free(struct bench_mem_info *info __maybe_unused,
>  		     struct bench_params *p __maybe_unused,
>  		     void **src, void **dst)
>  {
> -	free(*dst);
> -	free(*src);
> +	bench_munmap(*dst, p->size);
> +	bench_munmap(*src, p->size);
>  
>  	*dst = *src = NULL;
>  }
> -- 
> 2.43.5
>