On 18 Aug 2025, at 4:33, David Hildenbrand wrote:
> On 15.08.25 04:39, Zi Yan wrote:
>> and rename it to is_backed_by_folio().
>>
>> is_backed_by_folio() checks if the given vaddr is backed a folio with
>> a given order. It does so by:
>> 1. getting the pfn of the vaddr;
>> 2. checking kpageflags of the pfn;
>>
>> if order is greater than 0:
>> 3. checking kpageflags of the head pfn;
>> 4. checking kpageflags of all tail pfns.
>>
>> pmd_order is added to split_huge_page_test.c and replaces max_order.
>>
>> Signed-off-by: Zi Yan <[email protected]>
>> ---
>> .../selftests/mm/split_huge_page_test.c | 90 ++++++++++++++-----
>> tools/testing/selftests/mm/vm_util.c | 13 +++
>> tools/testing/selftests/mm/vm_util.h | 4 +
>> 3 files changed, 84 insertions(+), 23 deletions(-)
>>
>> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c
>> b/tools/testing/selftests/mm/split_huge_page_test.c
>> index 89d3dc08fe4c..80f718ca21c7 100644
>> --- a/tools/testing/selftests/mm/split_huge_page_test.c
>> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
>> @@ -25,6 +25,7 @@
>> uint64_t pagesize;
>> unsigned int pageshift;
>> uint64_t pmd_pagesize;
>> +unsigned int pmd_order;
>> #define SPLIT_DEBUGFS "/sys/kernel/debug/split_huge_pages"
>> #define SMAP_PATH "/proc/self/smaps"
>> @@ -34,27 +35,71 @@ 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))
>> -static int is_backed_by_thp(char *vaddr, int pagemap_file, int
>> kpageflags_file)
>> +static int is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
>> + int kpageflags_fd)
>
> Could we convert this into a bool and simply return "false" on error instead
> of "-"? These tristate returns for a "is_*" function are a bit unfortunate.
OK.
>
>> {
>> - uint64_t paddr;
>> - uint64_t page_flags;
>> + unsigned long pfn_head;
>> + uint64_t pfn_flags;
>> + unsigned long pfn;
>> + unsigned long i;
>> - if (pagemap_file) {
>> - pread(pagemap_file, &paddr, sizeof(paddr),
>> - ((long)vaddr >> pageshift) * sizeof(paddr));
>> + if (pagemap_fd == -1 || kpageflags_fd == -1)
>> + goto fail;
>
> Should we rather expect that callers make sure these are valid? In
> particular, because split_pte_mapped_thp() seems to ksft_exit_fail_msg()
> already.
Sure.
>
>> - if (kpageflags_file) {
>> - pread(kpageflags_file, &page_flags, sizeof(page_flags),
>> - (paddr & PFN_MASK) * sizeof(page_flags));
>> + pfn = pagemap_get_pfn(pagemap_fd, vaddr);
>
> Hm, if it's swapped out we would get intermittent errors, but that just seems
> hard to avoid. The caller could mock to avoid swapout.
>
> Memory migration is another possible problem ...
>
> But this is nothing new regarding your patch, so no need to worry for now.
Right. The function is only used by PTE-mapped THP split and I assume swapping
and migration would not happen. If this function is used more broadly, it
will need to take care of cases.
>
> [...]
>
>> +int get_pfn_flags(unsigned long pfn, int kpageflags_fd, uint64_t *flags)
>> +{
>> + size_t count;
>> +
>> + count = pread(kpageflags_fd, flags, sizeof(*flags),
>> + pfn * sizeof(*flags));
>> +
>> + if (count != sizeof(*flags))
>> + return -1;
>> +
>> + return 0;
>> +}
>
> I would have called this function "pageflags_get()" to resemble "pagemap_get"
OK. Will rename it.
Thanks.
--
Best Regards,
Yan, Zi
