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[2003:d8:2f12:d400:ed3c:fb0c:1ec0:c628]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-74058deb363sm10783439b3a.73.2025.05.07.03.03.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 07 May 2025 03:03:56 -0700 (PDT) Message-ID: <887fb371-409e-4dad-b4ff-38b85bfddf95@redhat.com> Date: Wed, 7 May 2025 12:03:50 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/3] mm: Add generic helper to hint a large folio To: Dev Jain , akpm@linux-foundation.org Cc: Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, vbabka@suse.cz, jannh@google.com, pfalcato@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, peterx@redhat.com, ryan.roberts@arm.com, mingo@kernel.org, libang.li@antgroup.com, maobibo@loongson.cn, zhengqi.arch@bytedance.com, baohua@kernel.org, anshuman.khandual@arm.com, willy@infradead.org, ioworker0@gmail.com, yang@os.amperecomputing.com References: <20250506050056.59250-1-dev.jain@arm.com> <20250506050056.59250-3-dev.jain@arm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: CDB0F2000D X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: ne61xsebgsnikie1yziyz4cqagu6ae1a X-HE-Tag: 1746612240-127657 X-HE-Meta: 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 nqt61Fj+ PO9iqkdIVskCYsvzw/sDg8vsQ03CMvJPn4Da7bYL77eyUQ/cLfWbiEkKFXkjm0XoBm1vphW+YeIAp3TE= 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 06.05.25 07:00, Dev Jain wrote: > To use PTE batching, we want to determine whether the folio mapped by > the PTE is large, thus requiring the use of vm_normal_folio(). We want > to avoid the cost of vm_normal_folio() if the code path doesn't already > require the folio. For arm64, pte_batch_hint() does the job. To generalize > this hint, add a helper which will determine whether two consecutive PTEs > point to consecutive PFNs, in which case there is a high probability that > the underlying folio is large. > > Signed-off-by: Dev Jain > --- > include/linux/pgtable.h | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index b50447ef1c92..28e21fcc7837 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -369,6 +369,22 @@ static inline pgd_t pgdp_get(pgd_t *pgdp) > } > #endif > > +/* Caller must ensure that ptep + 1 exists */ > +static inline bool maybe_contiguous_pte_pfns(pte_t *ptep, pte_t pte) > +{ > + pte_t *next_ptep, next_pte; > + > + if (pte_batch_hint(ptep, pte) != 1) > + return true; > + > + next_ptep = ptep + 1; > + next_pte = ptep_get(next_ptep); > + if (!pte_present(next_pte)) > + return false; > + > + return unlikely(pte_pfn(next_pte) - pte_pfn(pte) == PAGE_SIZE); > +} So, where we want to use that is: if (pte_present(old_pte)) { if ((max_nr != 1) && maybe_contiguous_pte_pfns(old_ptep, old_pte)) { struct folio *folio = vm_normal_folio(vma, old_addr, old_pte); if (folio && folio_test_large(folio)) nr = folio_pte_batch(folio, old_addr, old_ptep, old_pte, max_nr, fpb_flags, NULL, NULL, NULL); } } where we won't need the folio later. But want it all part of the same folio? And the simpler version would be if (pte_present(old_pte)) { if (max_nr != 1) { struct folio *folio = vm_normal_folio(vma, old_addr, old_pte); if (folio && folio_test_large(folio)) nr = folio_pte_batch(folio, old_addr, old_ptep, old_pte, max_nr, fpb_flags, NULL, NULL, NULL); } } Two things come to mind: (1) Do we *really* care about the vm_normal_folio() + folio_test_large() call that much, that you have to add this optimization ahead of times ? :) (2) Do we really need "must be part of the same folio", or could be just batch over present ptes that map consecutive PFNs? In that case, a helper that avoids folio_pte_batch() completely might be better. -- Cheers, David / dhildenb