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 07/19] selftests/mm: move is_backed_by_folio() into vm_util
Date: Tue, 18 Aug 2026 11:14:42 +0100 [thread overview]
Message-ID: <aoQwizWbYM7_T72f@lucifer> (raw)
In-Reply-To: <20260815015901.1236937-8-kirill@shutemov.name>
On Sat, Aug 15, 2026 at 02:58:49AM +0100, Kiryl Shutsemau wrote:
> From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
>
> Checking that an address range is backed by a folio of a given order is
> useful to any test that builds or collapses large folios. mTHP collapse
> coverage in the khugepaged selftest needs exactly that.
>
> split_huge_page_test.c already has the building block:
> is_backed_by_folio() reads the compound head and tail flags from
> /proc/kpageflags to classify the folio behind a page.
>
> Move it into vm_util so other tests can use it. No functional change.
>
> Assisted-by: Claude-Code:claude-opus-5
> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
> Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
LGTM so:
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
> ---
> .../selftests/mm/split_huge_page_test.c | 62 -------------------
> tools/testing/selftests/mm/vm_util.c | 62 +++++++++++++++++++
> tools/testing/selftests/mm/vm_util.h | 2 +
> 3 files changed, 64 insertions(+), 62 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
> index 86a603692826..0adfe7dde7e5 100644
> --- a/tools/testing/selftests/mm/split_huge_page_test.c
> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
> @@ -42,68 +42,6 @@ const char *kpageflags_proc = "/proc/kpageflags";
> int pagemap_fd;
> int kpageflags_fd;
>
> -static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
> - int kpageflags_fd)
> -{
> - const uint64_t folio_head_flags = KPF_THP | KPF_COMPOUND_HEAD;
> - const uint64_t folio_tail_flags = KPF_THP | KPF_COMPOUND_TAIL;
> - const unsigned long nr_pages = 1UL << order;
> - unsigned long pfn_head;
> - uint64_t pfn_flags;
> - unsigned long pfn;
> - unsigned long i;
> -
> - pfn = pagemap_get_pfn(pagemap_fd, vaddr);
> -
> - /* non present page */
> - if (pfn == -1UL)
> - return false;
> -
> - if (pageflags_get(pfn, kpageflags_fd, &pfn_flags))
> - goto fail;
> -
> - /* check for order-0 pages */
> - if (!order) {
> - if (pfn_flags & (folio_head_flags | folio_tail_flags))
> - return false;
> - return true;
> - }
> -
> - /* non THP folio */
> - if (!(pfn_flags & KPF_THP))
> - return false;
> -
> - pfn_head = pfn & ~(nr_pages - 1);
> -
> - if (pageflags_get(pfn_head, kpageflags_fd, &pfn_flags))
> - goto fail;
> -
> - /* head PFN has no compound_head flag set */
> - if ((pfn_flags & folio_head_flags) != folio_head_flags)
> - return false;
> -
> - /* check all tail PFN flags */
> - for (i = 1; i < nr_pages; i++) {
> - if (pageflags_get(pfn_head + i, kpageflags_fd, &pfn_flags))
> - goto fail;
> - if ((pfn_flags & folio_tail_flags) != folio_tail_flags)
> - return false;
> - }
> -
> - /*
> - * check the PFN after this folio, but if its flags cannot be obtained,
> - * assume this folio has the expected order
> - */
> - if (pageflags_get(pfn_head + nr_pages, kpageflags_fd, &pfn_flags))
> - return true;
> -
> - /* If we find another tail page, then the folio is larger. */
> - return (pfn_flags & folio_tail_flags) != folio_tail_flags;
> -fail:
> - ksft_exit_fail_msg("Failed to get folio info\n");
> - return false;
> -}
> -
> static int check_after_split_folio_orders(char *vaddr_start, size_t len,
> int pagemap_fd, int kpageflags_fd, int orders[], int nr_orders)
> {
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index 80bc9f597b52..5db1a7774f49 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -494,6 +494,68 @@ int pageflags_get(unsigned long pfn, int kpageflags_fd, uint64_t *flags)
> return 0;
> }
>
> +bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
> + int kpageflags_fd)
> +{
> + const uint64_t folio_head_flags = KPF_THP | KPF_COMPOUND_HEAD;
> + const uint64_t folio_tail_flags = KPF_THP | KPF_COMPOUND_TAIL;
> + const unsigned long nr_pages = 1UL << order;
> + unsigned long pfn_head;
> + uint64_t pfn_flags;
> + unsigned long pfn;
> + unsigned long i;
> +
> + pfn = pagemap_get_pfn(pagemap_fd, vaddr);
> +
> + /* non present page */
> + if (pfn == -1UL)
> + return false;
> +
> + if (pageflags_get(pfn, kpageflags_fd, &pfn_flags))
> + goto fail;
> +
> + /* check for order-0 pages */
> + if (!order) {
> + if (pfn_flags & (folio_head_flags | folio_tail_flags))
> + return false;
> + return true;
> + }
> +
> + /* non THP folio */
> + if (!(pfn_flags & KPF_THP))
> + return false;
> +
> + pfn_head = pfn & ~(nr_pages - 1);
> +
> + if (pageflags_get(pfn_head, kpageflags_fd, &pfn_flags))
> + goto fail;
> +
> + /* head PFN has no compound_head flag set */
> + if ((pfn_flags & folio_head_flags) != folio_head_flags)
> + return false;
> +
> + /* check all tail PFN flags */
> + for (i = 1; i < nr_pages; i++) {
> + if (pageflags_get(pfn_head + i, kpageflags_fd, &pfn_flags))
> + goto fail;
> + if ((pfn_flags & folio_tail_flags) != folio_tail_flags)
> + return false;
> + }
> +
> + /*
> + * check the PFN after this folio, but if its flags cannot be obtained,
> + * assume this folio has the expected order
> + */
> + if (pageflags_get(pfn_head + nr_pages, kpageflags_fd, &pfn_flags))
> + return true;
> +
> + /* If we find another tail page, then the folio is larger. */
> + return (pfn_flags & folio_tail_flags) != folio_tail_flags;
> +fail:
> + ksft_exit_fail_msg("Failed to get folio info\n");
> + return false;
> +}
> +
> /* If `ioctls' non-NULL, the allowed ioctls will be returned into the var */
> int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
> bool miss, bool wp, bool minor, uint64_t *ioctls)
> diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
> index 9a49af88702e..56a28ce7d029 100644
> --- a/tools/testing/selftests/mm/vm_util.h
> +++ b/tools/testing/selftests/mm/vm_util.h
> @@ -97,6 +97,8 @@ int64_t allocate_transhuge(void *ptr, int pagemap_fd);
> int pageflags_get(unsigned long pfn, int kpageflags_fd, uint64_t *flags);
> int gather_folio_orders(char *vaddr_start, size_t len,
> int pagemap_fd, int kpageflags_fd, int orders[], int nr_orders);
> +bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
> + int kpageflags_fd);
>
> int uffd_register(int uffd, void *addr, uint64_t len,
> bool miss, bool wp, bool minor);
> --
> 2.54.0
>
--
Cheers, Lorenzo
next prev parent reply other threads:[~2026-08-18 10:15 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) [this message]
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)
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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