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Message-ID: <B13F65A9-B001-4494-A060-23D95055553F@nvidia.com>
Date: Mon, 11 Aug 2025 14:39:08 -0400
From: Zi Yan <ziy@...dia.com>
To: Wei Yang <richard.weiyang@...il.com>
Cc: wang lian <lianux.mm@...il.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
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 v2 2/3] selftests/mm: add check_folio_orders() helper.
On 9 Aug 2025, at 16:18, Wei Yang wrote:
> On Fri, Aug 08, 2025 at 03:01:43PM -0400, 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>
>> ---
>> .../selftests/mm/split_huge_page_test.c | 4 +-
>> tools/testing/selftests/mm/vm_util.c | 133 ++++++++++++++++++
>> tools/testing/selftests/mm/vm_util.h | 7 +
>> 3 files changed, 141 insertions(+), 3 deletions(-)
>>
>> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
>> index cb364c5670c6..5ab488fab1cd 100644
>> --- a/tools/testing/selftests/mm/split_huge_page_test.c
>> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
>> @@ -34,8 +34,6 @@ uint64_t pmd_pagesize;
>> #define PID_FMT_OFFSET "%d,0x%lx,0x%lx,%d,%d"
>> #define PATH_FMT "%s,0x%lx,0x%lx,%d"
>>
>> -#define PFN_MASK ((1UL<<55)-1)
>> -#define KPF_THP (1UL<<22)
>> #define GET_ORDER(nr_pages) (31 - __builtin_clz(nr_pages))
>>
>> int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
>> @@ -49,7 +47,7 @@ int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
>>
>> if (kpageflags_file) {
>> pread(kpageflags_file, &page_flags, sizeof(page_flags),
>> - (paddr & PFN_MASK) * sizeof(page_flags));
>> + PAGEMAP_PFN(paddr) * sizeof(page_flags));
>>
>
> is_backed_by_thp() shares similar logic as get_page_flags(), I am thinking we can
> leverage get_page_flags() here.
I was lazy for this one. I will use check_folio_orders() in the next version.
>
>> return !!(page_flags & KPF_THP);
>> }
>> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
>> index 6a239aa413e2..41d50b74b2f6 100644
>> --- a/tools/testing/selftests/mm/vm_util.c
>> +++ b/tools/testing/selftests/mm/vm_util.c
>> @@ -338,6 +338,139 @@ int detect_hugetlb_page_sizes(size_t sizes[], int max)
>> return count;
>> }
>>
>> +static int get_page_flags(char *vaddr, int pagemap_file, int kpageflags_file,
>> + uint64_t *flags)
>> +{
>
> Nit.
>
> In vm_util.c, we usually name the file descriptor as xxx_fd.
OK. I can rename them.
>
>> + unsigned long pfn;
>> + size_t count;
>> +
>> + pfn = pagemap_get_pfn(pagemap_file, vaddr);
>> + /*
>> + * Treat non-present page as a page without any flag, so that
>> + * gather_folio_orders() just record the current folio order.
>> + */
>> + if (pfn == -1UL) {
>> + *flags = 0;
>> + return 0;
>> + }
>> +
>> + count = pread(kpageflags_file, flags, sizeof(*flags),
>> + pfn * sizeof(*flags));
>> +
>> + if (count != sizeof(*flags))
>> + return -1;
>> +
>> + return 0;
>> +}
>> +
>
> Maybe a simple document here would be helpful.
Will do.
>
>> +static int gather_folio_orders(char *vaddr_start, size_t len,
>> + int pagemap_file, int kpageflags_file,
>> + int orders[], int nr_orders)
>> +{
>> + uint64_t page_flags = 0;
>> + int cur_order = -1;
>> + char *vaddr;
>> +
>> + if (!pagemap_file || !kpageflags_file)
>> + return -1;
>> + if (nr_orders <= 0)
>> + return -1;
>> +
>> + for (vaddr = vaddr_start; vaddr < vaddr_start + len; ) {
>> + char *next_folio_vaddr;
>> + int status;
>> +
>> + if (get_page_flags(vaddr, 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]++;
>> + vaddr += psize();
>> + continue;
>> + }
>> +
>> + /* skip non thp compound pages */
>> + if (!(page_flags & KPF_THP)) {
>> + vaddr += psize();
>> + 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_vaddr = vaddr + (1UL << (cur_order + pshift()));
>> +
>> + if (next_folio_vaddr >= vaddr_start + len)
>> + break;
>
> Would we skip order 1 folio at the last position?
>
> For example, vaddr_start is 0x2000, len is 0x2000 and the folio at vaddr_start
> is an order 1 folio, whose size is exactly 0x2000.
>
> Then we will get next_folio_vaddr == vaddr_start + len.
>
> Could that happen?
No. After the loop, there is code checking cur_order and updating orders[].
>
>> +
>> + while (!(status = get_page_flags(next_folio_vaddr, 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))) {
>
> Maybe we can put them into one line.
Sure.
>
>> + if (cur_order < nr_orders) {
>> + orders[cur_order]++;
>> + cur_order = -1;
>> + vaddr = next_folio_vaddr;
>> + }
>> + break;
>> + }
>> +
>> + /* not a head nor a tail in a THP? */
>> + if (!(page_flags & KPF_COMPOUND_TAIL))
>> + return -1;
>> +
>> + cur_order++;
>> + next_folio_vaddr = vaddr + (1UL << (cur_order + pshift()));
>> + }
>
> The while loop share similar logic as the outer for loop. Is it possible
> reduce some duplication?
Outer loop is to filter order-0 and non head pages and while loop is
to find current THP/mTHP orders. It would be messy to combine them.
But feel free to provide ideas if you see a way.
>
>> +
>> + if (status)
>> + return status;
>> + }
>> + if (cur_order > 0 && cur_order < nr_orders)
>> + orders[cur_order]++;
>> + return 0;
>> +}
>> +
>> +int check_folio_orders(char *vaddr_start, size_t len, int pagemap_file,
>> + int kpageflags_file, int orders[], int nr_orders)
>> +{
>> + int *vaddr_orders;
>> + int status;
>> + int i;
>> +
>> + vaddr_orders = (int *)malloc(sizeof(int) * nr_orders);
>> +
>
> I took a look into thp_setting.h, where defines an array with NR_ORDERS
> element which is 20. Maybe we can leverage it here, since we don't expect the
> order to be larger.
>
20 is too large for current use. We can revisit this when the function
gets more users.
>> + if (!vaddr_orders)
>> + ksft_exit_fail_msg("Cannot allocate memory for vaddr_orders");
>> +
>> + memset(vaddr_orders, 0, sizeof(int) * nr_orders);
>> + status = gather_folio_orders(vaddr_start, len, pagemap_file,
>> + kpageflags_file, vaddr_orders, nr_orders);
>> + if (status)
>> + return status;
>> +
>> + status = 0;
>> + for (i = 0; i < nr_orders; i++)
>> + if (vaddr_orders[i] != orders[i]) {
>> + ksft_print_msg("order %d: expected: %d got %d\n", i,
>> + orders[i], vaddr_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 1843ad48d32b..02e3f1e7065b 100644
>> --- a/tools/testing/selftests/mm/vm_util.h
>> +++ b/tools/testing/selftests/mm/vm_util.h
>> @@ -18,6 +18,11 @@
>> #define PM_SWAP BIT_ULL(62)
>> #define PM_PRESENT BIT_ULL(63)
>>
>> +#define KPF_COMPOUND_HEAD BIT_ULL(15)
>> +#define KPF_COMPOUND_TAIL BIT_ULL(16)
>> +#define KPF_THP BIT_ULL(22)
>> +
>> +
>> /*
>> * Ignore the checkpatch warning, we must read from x but don't want to do
>> * anything with it in order to trigger a read page fault. We therefore must use
>> @@ -85,6 +90,8 @@ 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(char *vaddr_start, size_t len, 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);
>> --
>> 2.47.2
>
> --
> Wei Yang
> Help you, Help me
Best Regards,
Yan, Zi
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