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 FKO6goLz 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 1 Sep 2025, at 9:03, David Hildenbrand wrote: > On 01.09.25 14:56, Zi Yan wrote: >> On 1 Sep 2025, at 3:22, David Hildenbrand wrote: >> >>> On 31.08.25 04:27, Wei Yang wrote: >>> >>> Subject: "selftests/mm: verify page content after remapping PMD throu= gh PTEs" >>> >>>> After mremap(), add a check on content to see whether mremap corrupt= >>>> data. >>>> >>>> Signed-off-by: Wei Yang >>>> >>>> --- >>>> v2: add check on content instead of just test backed folio >>> >>> I'm confused, don't we have that exact check later in the function? >>> >>> Your v1 might have been better, unless I am missing something. >>> >>>> --- >>>> tools/testing/selftests/mm/split_huge_page_test.c | 6 +++++- >>>> 1 file changed, 5 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/too= ls/testing/selftests/mm/split_huge_page_test.c >>>> index 10ae65ea032f..229b6dcabece 100644 >>>> --- a/tools/testing/selftests/mm/split_huge_page_test.c >>>> +++ b/tools/testing/selftests/mm/split_huge_page_test.c >>>> @@ -423,10 +423,14 @@ static void split_pte_mapped_thp(void) >>>> /* smap does not show THPs after mremap, use kpageflags instead= */ >>>> thp_size =3D 0; >>>> - for (i =3D 0; i < pagesize * 4; i++) >>>> + for (i =3D 0; i < pagesize * 4; i++) { >>>> + if (pte_mapped[i] !=3D (char)i) >>>> + ksft_exit_fail_msg("%ld byte corrupted\n", i); >>>> + >>>> if (i % pagesize =3D=3D 0 && >>>> is_backed_by_folio(&pte_mapped[i], pmd_order, pagemap_fd, k= pageflags_fd)) >>>> thp_size++; >>>> + } >>>> if (thp_size !=3D 4) >>>> ksft_exit_fail_msg("Some THPs are missing during mremap\n"); >>> >>> I'm a bit confused with this test in general. >>> >>> We do a >>> >>> pte_mapped =3D mremap(one_page, pagesize, pagesize, MREMAP_MAYMOVE); >>> >>> which I read as a "NOP". >>> >>> Questions >>> >>> (a) Will this actually do anything? Also, maybe it does now, but can'= t the kernel just optimize that out in the future? >> >> It remaps each subpage of 4 PMD THPs into a contiguous 2MB vaddr range= and >> perform split on that range. > > I'm afraid I am missing the "why". > > I would have thought that a "split_pte_mapped_thp" test would want to p= te-map THPs > to the see if they can be split. > > Why is the mremap required? IOW, what exactly is the test trying to tes= t that > exceeds "split_pte_mapped_thp" ? IMHO, it is an interesting test case for splitting a THP when only a subp= age is mapped into a vaddr range and in a contiguous vaddr each page comes fr= om different THPs. The mprotect test case you are mentioning would still hav= e all subpages mapped by contiguous vaddrs. But if you think both are just testing PTE-mapped THPs, feel free to repl= ace the existing one with the mprotect test case. In addition, is_backed_by_folio= () can be reverted back to its prior version, since it no longer needs to ha= ndle the case where subpages from different THPs can be mapped into a vaddr ra= nge. -- Best Regards, Yan, Zi