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Message-ID: <898EC7C6-8AFE-4CED-AED7-C59C5CC03EB6@nvidia.com>
Date: Thu, 07 Aug 2025 13:02:31 -0400
From: Zi Yan <ziy@...dia.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
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 7 Aug 2025, at 2:49, Baolin Wang wrote:
> 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?
Sure.
>
>> +
>> + 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'?
>
Sure.
>> + 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)?
OK. I can change it to malloc.
Thanks.
>
>> + 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);
--
Best Regards,
Yan, Zi
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