From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
To: Kiryl Shutsemau <kirill@shutemov.name>
Cc: akpm@linux-foundation.org, david@kernel.org,
nico.pache@linux.dev, baolin.wang@linux.alibaba.com,
baohua@kernel.org, dev.jain@arm.com, hughd@google.com,
lance.yang@linux.dev, liam@infradead.org, mhocko@suse.com,
rppt@kernel.org, ryan.roberts@arm.com, shuah@kernel.org,
surenb@google.com, usama.arif@linux.dev, vbabka@kernel.org,
ziy@nvidia.com, usama.anjum@arm.com, agordeev@linux.ibm.com,
linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
linux-kernel@vger.kernel.org, kas@kernel.org
Subject: Re: [PATCH v4 09/19] selftests/mm: add folio-order detection self-check
Date: Tue, 18 Aug 2026 11:30:06 +0100 [thread overview]
Message-ID: <aoQzXhP0W0FVsvTp@lucifer> (raw)
In-Reply-To: <20260815015901.1236937-10-kirill@shutemov.name>
On Sat, Aug 15, 2026 at 02:58:51AM +0100, Kiryl Shutsemau wrote:
> From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
>
> The khugepaged mTHP tests detect collapse results with the vm_util
> folio-order helpers rather than smaps AnonHugePages, which only sees PMD
> mappings. If those helpers are wrong, every case built on them is wrong
> the same way, and nothing says so.
>
> Check them directly. For every anon THP order the kernel supports, fault
> memory in with only that order enabled. Require the helpers to classify
> the backing as exactly that order: not a neighbouring order, and 4K-backed
> memory as order 0.
>
> Run it in the thp category, ahead of ./khugepaged, so a broken helper is
> reported as itself rather than as a collapse failure. Verified on x86-64
> 4K (orders 0, 2-9) and arm64 64K (orders 0, 2-13).
>
> The test needs ALIGN(), which hmm-tests.c and migration.c each defined
> privately. Move it to vm_util.h and drop both copies.
Also:
uffd-unit-tests defines ALIGN_UP()...
And really you probably want to match the kernel convention of ALIGN()
defaulting to align-up (for some reason) and name this ALIGN_DOWN() to be
consistent and avoid confusion BUT...
Since the tests already do this mistake I guess it's not so bad to share the
define and propagate it for now I suppose.
>
> Assisted-by: Claude-Code:claude-opus-5
> Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
> Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
> ---
> tools/testing/selftests/mm/Makefile | 1 +
> .../testing/selftests/mm/folio_order_check.c | 137 ++++++++++++++++++
> tools/testing/selftests/mm/hmm-tests.c | 1 -
> tools/testing/selftests/mm/migration.c | 1 -
> tools/testing/selftests/mm/run_vmtests.sh | 2 +
> tools/testing/selftests/mm/vm_util.h | 2 +
> 6 files changed, 142 insertions(+), 2 deletions(-)
> create mode 100644 tools/testing/selftests/mm/folio_order_check.c
>
> diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
> index 2d5366196e30..2093fcf6e915 100644
> --- a/tools/testing/selftests/mm/Makefile
> +++ b/tools/testing/selftests/mm/Makefile
> @@ -104,6 +104,7 @@ TEST_GEN_FILES += guard-regions
> TEST_GEN_FILES += merge
> TEST_GEN_FILES += rmap
> TEST_GEN_FILES += folio_split_race_test
> +TEST_GEN_FILES += folio_order_check
>
> ifneq ($(ARCH),arm64)
> TEST_GEN_FILES += soft-dirty
> diff --git a/tools/testing/selftests/mm/folio_order_check.c b/tools/testing/selftests/mm/folio_order_check.c
> new file mode 100644
> index 000000000000..93030a42c3cc
> --- /dev/null
> +++ b/tools/testing/selftests/mm/folio_order_check.c
> @@ -0,0 +1,137 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Self-check for the vm_util folio-order detection helpers,
> + * is_backed_by_folio() and is_range_backed_by_folio_orders().
> + *
> + * For every anon THP order the kernel supports, fault memory in with only
> + * that order enabled and verify the helpers report exactly that order:
> + * not a neighbouring order, and plain 4K memory as order 0. The helpers
> + * are what the khugepaged mTHP tests use to detect collapse results, so
> + * they must agree with the kernel's own idea of the backing before any
> + * collapse test relies on them.
> + */
> +#define _GNU_SOURCE
> +#include <fcntl.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <sys/mman.h>
> +#include <unistd.h>
> +
> +#include "kselftest.h"
> +#include "vm_util.h"
> +#include "hugepage_settings.h"
> +
> +static int pagemap_fd;
> +static int kpageflags_fd;
> +
> +/* mmap an anon VMA of exactly @size bytes at a @size-aligned address. */
> +static char *alloc_aligned(size_t size)
> +{
> + size_t len = size * 2;
> + uintptr_t aligned;
> + char *p;
> +
> + p = mmap(NULL, len, PROT_READ | PROT_WRITE,
> + MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> + if (p == MAP_FAILED)
> + ksft_exit_fail_perror("mmap()");
> +
> + aligned = ALIGN((uintptr_t)p, size);
> + if (aligned != (uintptr_t)p)
> + munmap(p, aligned - (uintptr_t)p);
> + if (aligned + size != (uintptr_t)p + len)
> + munmap((char *)aligned + size,
> + (uintptr_t)p + len - aligned - size);
> +
> + return (char *)aligned;
> +}
> +
> +/*
> + * Enable only @order (order 0: nothing), fault one aligned window in and
> + * check the helpers see exactly @order.
> + */
> +static void check_order(int order)
> +{
> + struct thp_settings settings = *thp_current_settings();
> + size_t size = psize() << order;
> + bool ok = true;
> + char *p;
> + int i;
> +
> + for (i = 0; i < NR_ORDERS; i++)
> + settings.hugepages[i].enabled = THP_NEVER;
> + if (order)
> + settings.hugepages[order].enabled = THP_ALWAYS;
> + thp_push_settings(&settings);
> +
> + p = alloc_aligned(size);
> + *p = 1;
> +
> + if (!is_range_backed_by_folio_orders(p, size, order,
> + pagemap_fd, kpageflags_fd)) {
> + ksft_print_msg("order %d not detected after fault\n", order);
> + ok = false;
> + }
> +
> + /* A lower order must be rejected: the folio is larger. */
> + if (order && is_range_backed_by_folio_orders(p, size, order - 1,
> + pagemap_fd,
> + kpageflags_fd)) {
> + ksft_print_msg("order %d also reported as order %d\n",
> + order, order - 1);
> + ok = false;
> + }
> +
> + /* Order 0 pages must not look like any large folio, and vice versa. */
> + if (order && is_range_backed_by_folio_orders(p, size, 0,
> + pagemap_fd,
> + kpageflags_fd)) {
> + ksft_print_msg("order %d also reported as order 0\n", order);
> + ok = false;
> + }
> +
> + munmap(p, size);
> + thp_pop_settings();
> +
> + ksft_test_result(ok, "order %d classified\n", order);
> +}
> +
> +int main(void)
> +{
> + struct thp_settings settings;
> + unsigned long orders;
> + int order;
> +
> + ksft_print_header();
> +
> + if (!thp_available())
> + ksft_exit_skip("Transparent Hugepages not available\n");
> +
> + pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
> + if (pagemap_fd < 0)
> + ksft_exit_fail_perror("open(/proc/self/pagemap)");
> + kpageflags_fd = open("/proc/kpageflags", O_RDONLY);
> + if (kpageflags_fd < 0)
> + ksft_exit_skip("open(\"/proc/kpageflags\") requires root\n");
> +
> + orders = thp_supported_orders();
> + if (!orders)
> + ksft_exit_skip("No supported THP orders\n");
> +
> + ksft_set_plan(__builtin_popcountl(orders) + 1);
> +
> + thp_save_settings();
> + thp_read_settings(&settings);
> + /* Base of the settings stack; the bottom entry is never popped. */
> + thp_push_settings(&settings);
> +
> + check_order(0);
> + for (order = 1; order < NR_ORDERS; order++) {
> + if (!(orders & (1UL << order)))
> + continue;
> + check_order(order);
> + }
> +
> +
> + ksft_finished();
> +}
> diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
> index e2642eca0d02..df426f9218e7 100644
> --- a/tools/testing/selftests/mm/hmm-tests.c
> +++ b/tools/testing/selftests/mm/hmm-tests.c
> @@ -65,7 +65,6 @@ enum {
> #define HMM_PATH_MAX 64
> #define NTIMES 10
>
> -#define ALIGN(x, a) (((x) + (a - 1)) & (~((a) - 1)))
> /* Just the flags we need, copied from mm.h: */
>
> #ifndef FOLL_WRITE
> diff --git a/tools/testing/selftests/mm/migration.c b/tools/testing/selftests/mm/migration.c
> index f19d53c69576..fd35f8a7b5b8 100644
> --- a/tools/testing/selftests/mm/migration.c
> +++ b/tools/testing/selftests/mm/migration.c
> @@ -20,7 +20,6 @@
>
> #define TWOMEG (2<<20)
> #define RUNTIME (20)
> -#define ALIGN(x, a) (((x) + (a - 1)) & (~((a) - 1)))
>
> HUGETLB_SETUP_DEFAULT_PAGES(1)
>
> diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
> index d09f9f6a384e..2652a7920b80 100755
> --- a/tools/testing/selftests/mm/run_vmtests.sh
> +++ b/tools/testing/selftests/mm/run_vmtests.sh
> @@ -402,6 +402,8 @@ CATEGORY="pfnmap" run_test ./pfnmap
> # COW tests
> CATEGORY="cow" run_test ./cow
>
> +CATEGORY="thp" run_test ./folio_order_check
> +
> CATEGORY="thp" run_test ./khugepaged
>
> CATEGORY="thp" run_test ./khugepaged -s 2
> diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
> index 39dfb18dc10c..ce05bce4670d 100644
> --- a/tools/testing/selftests/mm/vm_util.h
> +++ b/tools/testing/selftests/mm/vm_util.h
> @@ -10,6 +10,8 @@
> #include <linux/fs.h>
>
> #define BIT_ULL(nr) (1ULL << (nr))
> +#define ALIGN(x, a) (((x) + (a) - 1) & ~((a) - 1))
> +
> #define PM_SOFT_DIRTY BIT_ULL(55)
> #define PM_MMAP_EXCLUSIVE BIT_ULL(56)
> #define PM_UFFD_WP BIT_ULL(57)
> --
> 2.54.0
>
--
Cheers, Lorenzo
next prev parent reply other threads:[~2026-08-18 10:30 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-15 1:58 [PATCH v4 00/19] selftests/mm: improve khugepaged coverage Kiryl Shutsemau
2026-08-15 1:58 ` [PATCH v4 01/19] selftests/mm: raise the khugepaged test-case cap Kiryl Shutsemau
2026-08-18 9:11 ` Lorenzo Stoakes (ARM)
2026-08-15 1:58 ` [PATCH v4 02/19] selftests/mm: skip collapse_compound_extreme() where the PMD is too large Kiryl Shutsemau
2026-08-18 9:22 ` Lorenzo Stoakes (ARM)
2026-08-15 1:58 ` [PATCH v4 03/19] selftests/mm: scale khugepaged's collapse wait with the PMD size Kiryl Shutsemau
2026-08-18 10:04 ` Lorenzo Stoakes (ARM)
2026-08-15 1:58 ` [PATCH v4 04/19] selftests/mm: skip khugepaged page cache cases without a PMD folio Kiryl Shutsemau
2026-08-18 10:07 ` Lorenzo Stoakes (ARM)
2026-08-15 1:58 ` [PATCH v4 05/19] selftests/mm: make the swap cases' swapout reliable Kiryl Shutsemau
2026-08-18 10:11 ` Lorenzo Stoakes (ARM)
2026-08-15 1:58 ` [PATCH v4 06/19] selftests/mm: stop khugepaged during the MADV_COLLAPSE cases Kiryl Shutsemau
2026-08-18 10:12 ` Lorenzo Stoakes (ARM)
2026-08-15 1:58 ` [PATCH v4 07/19] selftests/mm: move is_backed_by_folio() into vm_util Kiryl Shutsemau
2026-08-18 10:14 ` Lorenzo Stoakes (ARM)
2026-08-15 1:58 ` [PATCH v4 08/19] selftests/mm: add folio-order check for address ranges Kiryl Shutsemau
2026-08-18 10:25 ` Lorenzo Stoakes (ARM)
2026-08-15 1:58 ` [PATCH v4 09/19] selftests/mm: add folio-order detection self-check Kiryl Shutsemau
2026-08-18 10:30 ` Lorenzo Stoakes (ARM) [this message]
2026-08-15 1:58 ` [PATCH v4 10/19] selftests/mm: add khugepaged completion barrier helper Kiryl Shutsemau
2026-08-18 10:34 ` Lorenzo Stoakes (ARM)
2026-08-15 1:58 ` [PATCH v4 11/19] selftests/mm: add order-parameterized khugepaged collapse cases Kiryl Shutsemau
2026-08-18 10:38 ` Lorenzo Stoakes (ARM)
2026-08-15 1:58 ` [PATCH v4 12/19] selftests/mm: parameterize the mixed-source collapse case by source order Kiryl Shutsemau
2026-08-18 10:47 ` Lorenzo Stoakes (ARM)
2026-08-15 1:58 ` [PATCH v4 13/19] selftests/mm: cover a shared-source collapse write race Kiryl Shutsemau
2026-08-15 1:58 ` [PATCH v4 14/19] selftests/mm: run every supported collapse order by default Kiryl Shutsemau
2026-08-15 1:58 ` [PATCH v4 15/19] selftests/mm: check that one khugepaged pass collapses one window Kiryl Shutsemau
2026-08-15 1:58 ` [PATCH v4 16/19] selftests/mm: add khugepaged race harness Kiryl Shutsemau
2026-08-15 1:58 ` [PATCH v4 17/19] selftests/mm: race collapse of windows with holes Kiryl Shutsemau
2026-08-15 1:59 ` [PATCH v4 18/19] selftests/mm: add memory-pressure threads to the khugepaged race harness Kiryl Shutsemau
2026-08-15 1:59 ` [PATCH v4 19/19] selftests/mm: zap whole PTE tables in " Kiryl Shutsemau
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