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Tue, 02 Sep 2025 12:59:50 -0700 (PDT) Date: Tue, 2 Sep 2025 19:59:49 +0000 From: Wei Yang To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v2 1/2] selftests/mm: split_huge_page_test: fix occasional is_backed_by_folio() wrong results Message-ID: <20250902195949.pfjv55in3cdhxhfg@master> Reply-To: Wei Yang References: <20250902162536.956465-1-david@redhat.com> <20250902162536.956465-2-david@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250902162536.956465-2-david@redhat.com> User-Agent: NeoMutt/20170113 (1.7.2) On Tue, Sep 02, 2025 at 06:25:35PM +0200, David Hildenbrand wrote: >When checking for actual tail or head pages of a folio, we must make >sure that the KPF_COMPOUND_HEAD/KPF_COMPOUND_TAIL flag is paired with >KPF_THP. > >For example, if we have another large folio after our large folio in >physical memory, our "pfn_flags & (KPF_THP | KPF_COMPOUND_TAIL" would ^ One nit here, we missed ) >trigger even though it's actually a head page of the next folio. > >If is_backed_by_folio() returns a wrong result, split_pte_mapped_thp() >can fail with "Some THPs are missing during mremap". > >Fix it by checking for head/tail pages of folios properly. Add >folio_tail_flags/folio_head_flags to improve readability and use these >masks also when just testing for any compound page. > >Fixes: 169b456b0162 ("selftests/mm: reimplement is_backed_by_thp() with more precise check") >Signed-off-by: David Hildenbrand Otherwise, Reviewed-by: Wei Yang -- Wei Yang Help you, Help me