On Tue, Sep 02, 2025 at 09:49:48AM +0200, David Hildenbrand wrote:
>> > + /*
>> > + * To challenge spitting code, we will mremap page[x] of the
>> > + * thp[x] into a smaller area, and trigger the split from that
>> > + * smaller area. This will end up replacing the PMD mappings in
>> > + * the thp_area by PTE mappings first, leaving the THPs unsplit.
>> > + */
This confuse me a little. How about move "and trigger the split from that
smaller area" to the end? So that I know mremap convert to pte-mapping and
leave thp unsplit. Then we do the split.
>> > + page_area = mmap(NULL, page_area_size, PROT_READ | PROT_WRITE,
>> > + MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
>> > + if (page_area == MAP_FAILED) {
>> > + ksft_test_result_fail("Fail to allocate memory: %s\n",
>> > strerror(errno));
>> > + goto out;
>> > + }
>> > - if (i % pagesize == 0 &&
>> > - !is_backed_by_folio(&pte_mapped[i], 0, pagemap_fd,
>> > kpageflags_fd))
>> > - thp_size++;
>> > + for (i = 0; i < nr_thps; i++) {
>> > + tmp = mremap(thp_area + pmd_pagesize * i + pagesize * i,
>> > + pagesize, pagesize, MREMAP_MAYMOVE|MREMAP_FIXED,
>> > + page_area + pagesize * i);
>>
>> Would this create one hole at the beginning of each 2M range and cause
>> splitting underlining THP?
>
>Yes, it will create a hole (this also happens in the old code).
>
>As the comment above it now states: "leaving the THPs unsplit"
>
>There is a check verifying that after this mremap code.
>
Thanks for clarifying. One nit to the comment above.
--
Wei Yang
Help you, Help me
