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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> 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) X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: B7DBEC000B X-Stat-Signature: zsgwxcktuuwi63a3u5fgdiipmxm7aftp X-Rspam-User: X-HE-Tag: 1756843192-490830 X-HE-Meta: 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 L097tCIY 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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 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