On Tue, Mar 18, 2025 at 05:43:41PM +0000, Ryan Roberts wrote:
> create_pagecache_thp_and_fd() was previously writing a file sized at
> twice the PMD size by making a per-byte write syscall. This was quite
> slow when the PMD size is 4M, but completely intolerable for 32M (PMD
> size for arm64's 16K page size), and 512M (PMD size for arm64's 64K page
> size).
>
> The byte pattern has a 256 byte period, so let's create a 1K buffer and
> fill it with exactly 4 periods. Then we can write the buffer as many
> times as is required to fill the file. This makes things much more
> tolerable.
>
> The test now passes for 16K page size. It still fails for 64K page size
> because MAX_PAGECACHE_ORDER is too small for 512M folio size (I think).
>
> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
> ---
> tools/testing/selftests/mm/split_huge_page_test.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
> index 3f353f3d070f..499333d75fff 100644
> --- a/tools/testing/selftests/mm/split_huge_page_test.c
> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
> @@ -5,6 +5,7 @@
> */
>
> #define _GNU_SOURCE
> +#include <assert.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <stdarg.h>
> @@ -361,6 +362,7 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd,
> {
> size_t i;
> int dummy = 0;
> + unsigned char buf[1024];
>
> srand(time(NULL));
>
> @@ -368,11 +370,12 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd,
> if (*fd == -1)
> ksft_exit_fail_msg("Failed to create a file at %s\n", testfile);
>
> - for (i = 0; i < fd_size; i++) {
> - unsigned char byte = (unsigned char)i;
> + assert(fd_size % sizeof(buf) == 0);
> + for (i = 0; i < sizeof(buf); i++)
> + buf[i] = (unsigned char)i;
> + for (i = 0; i < fd_size; i += sizeof(buf))
> + write(*fd, buf, sizeof(buf));
>
> - write(*fd, &byte, sizeof(byte));
> - }
> close(*fd);
> sync();
> *fd = open("/proc/sys/vm/drop_caches", O_WRONLY);
> --
> 2.43.0
>
>
Acked-by: Rafael Aquini <raquini@xxxxxxxxxx>
