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Tue, 11 Jun 2024 15:08:50 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id LH+fKoJoaGaTXAAAD6G6ig (envelope-from ); Tue, 11 Jun 2024 15:08:50 +0000 Date: Tue, 11 Jun 2024 17:08:45 +0200 From: Oscar Salvador To: Peter Xu Cc: Christophe Leroy , Andrew Morton , Jason Gunthorpe , Michael Ellerman , Nicholas Piggin , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v5 02/18] mm: Define __pte_leaf_size() to also take a PMD entry Message-ID: References: <172b11c93e0de7a84937af2da9f80bd17c56b8c9.1717955558.git.christophe.leroy@csgroup.eu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam03 X-Stat-Signature: 44zeud1sm54q39zpjnutgfsjrsyo6o43 X-Rspamd-Queue-Id: ECEBC180003 X-Rspam-User: X-HE-Tag: 1718118533-262352 X-HE-Meta: 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 1SI0C5/L QI5YwnmllzmuQC3sh+PNRhhnl3usj5ryXZXUf+Mk0v04MD4vIDPGUul6nvdVxTBiXTIGnkjanf9/TJSc3aDxHt2m9M+FtvuIRpLqr/8+xvT96jhY0woRw56jtUBgDDpnNcUWYwNI6RbGNW2mypRv91amql5HzbyJeJEhl7WwBfddvBedwA1bMANyPocHELnxCFWtci6H+QC5mPBtdPgvlnYh89MZ8ktua6Mzc4u2+da6brWqKy2n5JUQFVPB46tKBiBn+ 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, Jun 11, 2024 at 10:17:30AM -0400, Peter Xu wrote: > Oscar, > > On Tue, Jun 11, 2024 at 11:34:23AM +0200, Oscar Salvador wrote: > > Which means that they would be caught in the following code: > > > > ptl = pmd_huge_lock(pmd, vma); > > if (ptl) { > > - 8MB hugepages will be handled here > > smaps_pmd_entry(pmd, addr, walk); > > spin_unlock(ptl); > > } > > /* pte stuff */ > > ... > > Just one quick comment: I think there's one challenge though as this is > also not a generic "pmd leaf", but a pgtable page underneath. I think it > means smaps_pmd_entry() won't trivially work here, e.g., it will start to > do this: > > if (pmd_present(*pmd)) { > page = vm_normal_page_pmd(vma, addr, *pmd); > > Here vm_normal_page_pmd() will only work if pmd_leaf() satisfies its > definition as: > > * - It should contain a huge PFN, which points to a huge page larger than > * PAGE_SIZE of the platform. The PFN format isn't important here. > > But now it's a pgtable page, containing cont-ptes. Similarly, I think most > pmd_*() helpers will stop working there if we report it as a leaf. Heh, I think I managed to confuse myself. I do not why but I thought that static inline pte_t huge_ptep_get(struct mm_struct *mm, unsigned long addr, pte_t *ptep) { if (ptep_is_8m_pmdp(mm, addr, ptep)) ptep = pte_offset_kernel((pmd_t *)ptep, 0); return ptep_get(ptep); } would return the address of the pmd for 8MB hugepages, but it will return the address of the first pte? Then yeah, this will not work as I thought. The problem is that we do not have spare bits for 8xx to mark these ptes as cont-ptes or mark them pte as 8MB, so I do not see a clear path on how we could remove huge_ptep_get for 8xx. I am really curious though how we handle that for THP? Or THP on 8xx does not support that size? -- Oscar Salvador SUSE Labs