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Tue, 02 Sep 2025 01:13:42 -0700 (PDT) Date: Tue, 2 Sep 2025 08:13:42 +0000 From: Wei Yang To: David Hildenbrand Cc: Wei Yang , Zi Yan , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, baolin.wang@linux.alibaba.com, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [Patch v2] selftests/mm: check content to see whether mremap corrupt data Message-ID: <20250902081342.rthx5sopowmg4hyb@master> Reply-To: Wei Yang References: <20250831022701.2595-1-richard.weiyang@gmail.com> <61E58B7C-23D0-49FE-8D0C-CE0B672114E2@nvidia.com> <0a0b0018-9427-4201-bf53-6aeb251bc482@redhat.com> <1D88E773-C11E-4F28-A13A-1A681898198B@nvidia.com> <5a796574-0a3c-4040-b0bc-3ff757402759@redhat.com> <20250902025112.d2n3o4imeptppctd@master> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: C422B40003 X-Stat-Signature: wptzhd4naokgs1ooqermo8hukncgau3f X-Rspam-User: X-HE-Tag: 1756800824-165000 X-HE-Meta: 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 Ac3J6pOf 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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 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