Re: [PATCH 2/3] selftests/mm: hmm-tests: don't hardcode THP size to 2MB

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Mar 31, 2026 at 05:34:44PM +1100, Alistair Popple wrote:
> Several HMM tests hardcode TWOMEG as the THP size. This is wrong on
> architectures where the PMD size is not 2MB such as arm64 with 64K base

+1

But one question…

Can’t the THP size be derived via HPAGE_PMD_ORDER?

If not, then some DRM common code I’ve written will break on arm64.

Matt

> pages where THP is 512MB. Fix this by using read_pmd_pagesize() from
> vm_util instead.
> 
> While here also replace the custom file_read_ulong() helper used to
> parse the default hugetlbfs page size from /proc/meminfo with the
> existing default_huge_page_size() from vm_util.
> 
> [1] https://lore.kernel.org/linux-mm/8bd0396a-8997-4d2e-a13f-5aac033083d7@linux.dev/
> 
> Fixes: fee9f6d1b8df ("mm/hmm/test: add selftests for HMM")
> Fixes: 519071529d2a ("selftests/mm/hmm-tests: new tests for zone device THP migration")
> Reported-by: Zenghui Yu <zenghui.yu@linux.dev>
> Closes: https://lore.kernel.org/linux-mm/8bd0396a-8997-4d2e-a13f-5aac033083d7@linux.dev/
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
> ---
>  tools/testing/selftests/mm/hmm-tests.c | 83 +++++---------------------
>  1 file changed, 16 insertions(+), 67 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
> index e8328c89d855..788689497e92 100644
> --- a/tools/testing/selftests/mm/hmm-tests.c
> +++ b/tools/testing/selftests/mm/hmm-tests.c
> @@ -34,6 +34,7 @@
>   */
>  #include <lib/test_hmm_uapi.h>
>  #include <mm/gup_test.h>
> +#include <mm/vm_util.h>
>  
>  struct hmm_buffer {
>  	void		*ptr;
> @@ -548,7 +549,7 @@ TEST_F(hmm, anon_write_child)
>  
>  	for (migrate = 0; migrate < 2; ++migrate) {
>  		for (use_thp = 0; use_thp < 2; ++use_thp) {
> -			npages = ALIGN(use_thp ? TWOMEG : HMM_BUFFER_SIZE,
> +			npages = ALIGN(use_thp ? read_pmd_pagesize() : HMM_BUFFER_SIZE,
>  				       self->page_size) >> self->page_shift;
>  			ASSERT_NE(npages, 0);
>  			size = npages << self->page_shift;
> @@ -728,7 +729,7 @@ TEST_F(hmm, anon_write_huge)
>  	int *ptr;
>  	int ret;
>  
> -	size = 2 * TWOMEG;
> +	size = 2 * read_pmd_pagesize();
>  
>  	buffer = malloc(sizeof(*buffer));
>  	ASSERT_NE(buffer, NULL);
> @@ -744,7 +745,7 @@ TEST_F(hmm, anon_write_huge)
>  			   buffer->fd, 0);
>  	ASSERT_NE(buffer->ptr, MAP_FAILED);
>  
> -	size = TWOMEG;
> +	size /= 2;
>  	npages = size >> self->page_shift;
>  	map = (void *)ALIGN((uintptr_t)buffer->ptr, size);
>  	ret = madvise(map, size, MADV_HUGEPAGE);
> @@ -770,54 +771,6 @@ TEST_F(hmm, anon_write_huge)
>  	hmm_buffer_free(buffer);
>  }
>  
> -/*
> - * Read numeric data from raw and tagged kernel status files.  Used to read
> - * /proc and /sys data (without a tag) and from /proc/meminfo (with a tag).
> - */
> -static long file_read_ulong(char *file, const char *tag)
> -{
> -	int fd;
> -	char buf[2048];
> -	int len;
> -	char *p, *q;
> -	long val;
> -
> -	fd = open(file, O_RDONLY);
> -	if (fd < 0) {
> -		/* Error opening the file */
> -		return -1;
> -	}
> -
> -	len = read(fd, buf, sizeof(buf));
> -	close(fd);
> -	if (len < 0) {
> -		/* Error in reading the file */
> -		return -1;
> -	}
> -	if (len == sizeof(buf)) {
> -		/* Error file is too large */
> -		return -1;
> -	}
> -	buf[len] = '\0';
> -
> -	/* Search for a tag if provided */
> -	if (tag) {
> -		p = strstr(buf, tag);
> -		if (!p)
> -			return -1; /* looks like the line we want isn't there */
> -		p += strlen(tag);
> -	} else
> -		p = buf;
> -
> -	val = strtol(p, &q, 0);
> -	if (*q != ' ') {
> -		/* Error parsing the file */
> -		return -1;
> -	}
> -
> -	return val;
> -}
> -
>  /*
>   * Write huge TLBFS page.
>   */
> @@ -826,15 +779,13 @@ TEST_F(hmm, anon_write_hugetlbfs)
>  	struct hmm_buffer *buffer;
>  	unsigned long npages;
>  	unsigned long size;
> -	unsigned long default_hsize;
> +	unsigned long default_hsize = default_huge_page_size();
>  	unsigned long i;
>  	int *ptr;
>  	int ret;
>  
> -	default_hsize = file_read_ulong("/proc/meminfo", "Hugepagesize:");
> -	if (default_hsize < 0 || default_hsize*1024 < default_hsize)
> +	if (!default_hsize)
>  		SKIP(return, "Huge page size could not be determined");
> -	default_hsize = default_hsize*1024; /* KB to B */
>  
>  	size = ALIGN(TWOMEG, default_hsize);
>  	npages = size >> self->page_shift;
> @@ -1606,7 +1557,7 @@ TEST_F(hmm, compound)
>  	struct hmm_buffer *buffer;
>  	unsigned long npages;
>  	unsigned long size;
> -	unsigned long default_hsize;
> +	unsigned long default_hsize = default_huge_page_size();
>  	int *ptr;
>  	unsigned char *m;
>  	int ret;
> @@ -1614,10 +1565,8 @@ TEST_F(hmm, compound)
>  
>  	/* Skip test if we can't allocate a hugetlbfs page. */
>  
> -	default_hsize = file_read_ulong("/proc/meminfo", "Hugepagesize:");
> -	if (default_hsize < 0 || default_hsize*1024 < default_hsize)
> +	if (!default_hsize)
>  		SKIP(return, "Huge page size could not be determined");
> -	default_hsize = default_hsize*1024; /* KB to B */
>  
>  	size = ALIGN(TWOMEG, default_hsize);
>  	npages = size >> self->page_shift;
> @@ -2106,7 +2055,7 @@ TEST_F(hmm, migrate_anon_huge_empty)
>  	int *ptr;
>  	int ret;
>  
> -	size = TWOMEG;
> +	size = read_pmd_pagesize();
>  
>  	buffer = malloc(sizeof(*buffer));
>  	ASSERT_NE(buffer, NULL);
> @@ -2158,7 +2107,7 @@ TEST_F(hmm, migrate_anon_huge_zero)
>  	int ret;
>  	int val;
>  
> -	size = TWOMEG;
> +	size = read_pmd_pagesize();
>  
>  	buffer = malloc(sizeof(*buffer));
>  	ASSERT_NE(buffer, NULL);
> @@ -2221,7 +2170,7 @@ TEST_F(hmm, migrate_anon_huge_free)
>  	int *ptr;
>  	int ret;
>  
> -	size = TWOMEG;
> +	size = read_pmd_pagesize();
>  
>  	buffer = malloc(sizeof(*buffer));
>  	ASSERT_NE(buffer, NULL);
> @@ -2280,7 +2229,7 @@ TEST_F(hmm, migrate_anon_huge_fault)
>  	int *ptr;
>  	int ret;
>  
> -	size = TWOMEG;
> +	size = read_pmd_pagesize();
>  
>  	buffer = malloc(sizeof(*buffer));
>  	ASSERT_NE(buffer, NULL);
> @@ -2332,7 +2281,7 @@ TEST_F(hmm, migrate_partial_unmap_fault)
>  {
>  	struct hmm_buffer *buffer;
>  	unsigned long npages;
> -	unsigned long size = TWOMEG;
> +	unsigned long size = read_pmd_pagesize();
>  	unsigned long i;
>  	void *old_ptr;
>  	void *map;
> @@ -2398,7 +2347,7 @@ TEST_F(hmm, migrate_remap_fault)
>  {
>  	struct hmm_buffer *buffer;
>  	unsigned long npages;
> -	unsigned long size = TWOMEG;
> +	unsigned long size = read_pmd_pagesize();
>  	unsigned long i;
>  	void *old_ptr, *new_ptr = NULL;
>  	void *map;
> @@ -2498,7 +2447,7 @@ TEST_F(hmm, migrate_anon_huge_err)
>  	int *ptr;
>  	int ret;
>  
> -	size = TWOMEG;
> +	size = read_pmd_pagesize();
>  
>  	buffer = malloc(sizeof(*buffer));
>  	ASSERT_NE(buffer, NULL);
> @@ -2593,7 +2542,7 @@ TEST_F(hmm, migrate_anon_huge_zero_err)
>  	int *ptr;
>  	int ret;
>  
> -	size = TWOMEG;
> +	size = read_pmd_pagesize();
>  
>  	buffer = malloc(sizeof(*buffer));
>  	ASSERT_NE(buffer, NULL);
> -- 
> 2.53.0
>