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Message-ID: <dd2118cd-9209-43d5-9c73-8e3989931841@linux.alibaba.com>
Date: Thu, 7 Aug 2025 14:49:22 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Zi Yan <ziy@...dia.com>, David Hildenbrand <david@...hat.com>,
linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
Barry Song <baohua@...nel.org>, Vlastimil Babka <vbabka@...e.cz>,
Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>,
Michal Hocko <mhocko@...e.com>, Shuah Khan <shuah@...nel.org>,
linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 3/4] selftests/mm: add check_folio_orders() helper.
On 2025/8/6 10:20, Zi Yan wrote:
> The helper gathers an folio order statistics of folios within a virtual
> address range and checks it against a given order list. It aims to provide
> a more precise folio order check instead of just checking the existence of
> PMD folios.
>
> Signed-off-by: Zi Yan <ziy@...dia.com>
> ---
> tools/testing/selftests/mm/vm_util.c | 139 +++++++++++++++++++++++++++
> tools/testing/selftests/mm/vm_util.h | 2 +
> 2 files changed, 141 insertions(+)
>
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index 9dafa7669ef9..373621145b2a 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -17,6 +17,12 @@
> #define STATUS_FILE_PATH "/proc/self/status"
> #define MAX_LINE_LENGTH 500
>
> +#define PGMAP_PRESENT (1UL << 63)
> +#define KPF_COMPOUND_HEAD (1UL << 15)
> +#define KPF_COMPOUND_TAIL (1UL << 16)
> +#define KPF_THP (1UL << 22)
> +#define PFN_MASK ((1UL<<55)-1)
> +
> unsigned int __page_size;
> unsigned int __page_shift;
>
> @@ -338,6 +344,139 @@ int detect_hugetlb_page_sizes(size_t sizes[], int max)
> return count;
> }
>
> +static int get_page_flags(uint64_t vpn, int pagemap_file, int kpageflags_file,
> + uint64_t *flags)
> +{
> + uint64_t pfn;
> + size_t count;
> +
> + count = pread(pagemap_file, &pfn, sizeof(pfn),
> + vpn * sizeof(pfn));
> +
> + if (count != sizeof(pfn))
> + return -1;
> +
> + /*
> + * Treat non-present page as a page without any flag, so that
> + * gather_folio_orders() just record the current folio order.
> + */
> + if (!(pfn & PGMAP_PRESENT)) {
> + *flags = 0;
> + return 0;
> + }
It looks like you can reuse the helper pagemap_get_pfn() in this file?
> +
> + count = pread(kpageflags_file, flags, sizeof(*flags),
> + (pfn & PFN_MASK) * sizeof(*flags));
> +
> + if (count != sizeof(*flags))
> + return -1;
> +
> + return 0;
> +}
> +
> +static int gather_folio_orders(uint64_t vpn_start, size_t nr_pages,
In this file, other helper functions use userspace virtual address as
parameters, so can we consistently use virtual address for calculations
instead of the 'vpn_start'?
> + int pagemap_file, int kpageflags_file,
> + int orders[], int nr_orders)
> +{
> + uint64_t page_flags = 0;
> + int cur_order = -1;
> + uint64_t vpn;
> +
> + if (!pagemap_file || !kpageflags_file)
> + return -1;
> + if (nr_orders <= 0)
> + return -1;
> +
> + for (vpn = vpn_start; vpn < vpn_start + nr_pages; ) {
> + uint64_t next_folio_vpn;
> + int status;
> +
> + if (get_page_flags(vpn, pagemap_file, kpageflags_file, &page_flags))
> + return -1;
> +
> + /* all order-0 pages with possible false postive (non folio) */
> + if (!(page_flags & (KPF_COMPOUND_HEAD | KPF_COMPOUND_TAIL))) {
> + orders[0]++;
> + vpn++;
> + continue;
> + }
> +
> + /* skip non thp compound pages */
> + if (!(page_flags & KPF_THP)) {
> + vpn++;
> + continue;
> + }
> +
> + /* vpn points to part of a THP at this point */
> + if (page_flags & KPF_COMPOUND_HEAD)
> + cur_order = 1;
> + else {
> + /* not a head nor a tail in a THP? */
> + if (!(page_flags & KPF_COMPOUND_TAIL))
> + return -1;
> + continue;
> + }
> +
> + next_folio_vpn = vpn + (1 << cur_order);
> +
> + if (next_folio_vpn >= vpn_start + nr_pages)
> + break;
> +
> + while (!(status = get_page_flags(next_folio_vpn, pagemap_file,
> + kpageflags_file,
> + &page_flags))) {
> + /* next compound head page or order-0 page */
> + if ((page_flags & KPF_COMPOUND_HEAD) ||
> + !(page_flags & (KPF_COMPOUND_HEAD |
> + KPF_COMPOUND_TAIL))) {
> + if (cur_order < nr_orders) {
> + orders[cur_order]++;
> + cur_order = -1;
> + vpn = next_folio_vpn;
> + }
> + break;
> + }
> +
> + /* not a head nor a tail in a THP? */
> + if (!(page_flags & KPF_COMPOUND_TAIL))
> + return -1;
> +
> + cur_order++;
> + next_folio_vpn = vpn + (1 << cur_order);
> + }
> +
> + if (status)
> + return status;
> + }
> + if (cur_order > 0 && cur_order < nr_orders)
> + orders[cur_order]++;
> + return 0;
> +}
> +
> +int check_folio_orders(uint64_t vpn_start, size_t nr_pages, int pagemap_file,
> + int kpageflags_file, int orders[], int nr_orders)
> +{
> + int vpn_orders[nr_orders];
IIRC, we should avoid using VLA (variable length arrays)?
> + int status;
> + int i;
> +
> + memset(vpn_orders, 0, sizeof(int) * nr_orders);
> + status = gather_folio_orders(vpn_start, nr_pages, pagemap_file,
> + kpageflags_file, vpn_orders, nr_orders);
> + if (status)
> + return status;
> +
> + status = 0;
> + for (i = 0; i < nr_orders; i++)
> + if (vpn_orders[i] != orders[i]) {
> + ksft_print_msg("order %d: expected: %d got %d\n", i,
> + orders[i], vpn_orders[i]);
> + status = -1;
> + }
> +
> + return status;
> +}
> +
> /* 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 b55d1809debc..dee9504a6129 100644
> --- a/tools/testing/selftests/mm/vm_util.h
> +++ b/tools/testing/selftests/mm/vm_util.h
> @@ -85,6 +85,8 @@ bool check_huge_shmem(void *addr, int nr_hpages, uint64_t hpage_size);
> int64_t allocate_transhuge(void *ptr, int pagemap_fd);
> unsigned long default_huge_page_size(void);
> int detect_hugetlb_page_sizes(size_t sizes[], int max);
> +int check_folio_orders(uint64_t vpn_start, size_t nr_pages, int pagemap_file,
> + int kpageflags_file, int orders[], int nr_orders);
>
> int uffd_register(int uffd, void *addr, uint64_t len,
> bool miss, bool wp, bool minor);
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