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[2003:d8:2f2c:1e00:1e1e:7a32:e798:6457]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4532e13c187sm22369795e9.23.2025.06.12.07.16.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Jun 2025 07:16:25 -0700 (PDT) Message-ID: <7b03ba9d-5ace-4c1e-a415-544b471f19d7@redhat.com> Date: Thu, 12 Jun 2025 16:16:24 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] mm: huge_memory: disallow hugepages if the system-wide THP sysfs settings are disabled To: Baolin Wang , Lorenzo Stoakes Cc: akpm@linux-foundation.org, hughd@google.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <8eefb0809c598fadaa4a022634fba5689a4f3257.1749109709.git.baolin.wang@linux.alibaba.com> <1ec368c4-c4d8-41ea-b8a3-7d1fdb3ec358@redhat.com> <2ff65f37-efa9-4e96-9cdf-534d63ff154e@linux.alibaba.com> <953596b2-8749-493d-97eb-a5d8995d9ef8@redhat.com> <97a67b74-d473-455e-a05e-c85fe45da008@linux.alibaba.com> <201a1cc4-93fc-48e3-aeab-759ba8c8a47c@lucifer.local> <519c59e6-20ef-4edf-88b8-a71f38cbd2de@linux.alibaba.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12.06.25 16:13, Baolin Wang wrote: > > > On 2025/6/12 21:29, Lorenzo Stoakes wrote: >> On Thu, Jun 12, 2025 at 02:27:06PM +0100, Lorenzo Stoakes wrote: >> [snip] >> >>> I propose a compromise as I rather like your 'exclude never' negation bit. >>> >>> So: >>> >>> /* Strictly mask requested anonymous orders according to sysfs settings. */ >>> static inline unsigned long __thp_mask_anon_orders(unsigned long vm_flags, >>> unsigned long tva_flags, unsigned long orders) >>> { >>> const unsigned long always = READ_ONCE(huge_anon_orders_always); >>> const unsigned long madvise = READ_ONCE(huge_anon_orders_madvise); >>> const unsigned long inherit = READ_ONCE(huge_anon_orders_inherit);; >>> const unsigned long never = ~(always | madvise | inherit); >>> const bool inherit_enabled = hugepage_global_enabled(); >>> >>> /* Disallow orders that are set to NEVER directly ... */ >>> orders &= ~never; >>> >>> /* ... or through inheritance (global == NEVER). */ >>> if (!inherit_enabled) >>> orders &= ~inherit; >>> >>> /* >>> * Otherwise, we only enforce sysfs settings if asked. In addition, >>> * if the user sets a sysfs mode of madvise and if TVA_ENFORCE_SYSFS >>> * is not set, we don't bother checking whether the VMA has VM_HUGEPAGE >>> * set. >>> */ >>> if (!(tva_flags & TVA_ENFORCE_SYSFS)) >>> return orders; >>> >>> if (hugepage_global_always()) >>> return orders & (always | inherit); >>> >>> /* We already excluded never inherit above. */ >>> if (vm_flags & VM_HUGEPAGE) >>> return orders & (always | madvise | inherit); >> >> Of course... I immediately made a mistake... swap these two statements around. I >> thought it'd be 'neater' to do the first one first, but of course it means >> madvise (rather than inherit) orders don't get selected. >> >> This WHOLE THING needs refactoring. > > Personally, I think the 'exclude never' logic becomes more complicated. > I made a simpler change without adding a new helper. What do you think? > > static inline > unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma, > unsigned long vm_flags, > unsigned long tva_flags, > unsigned long orders) > { > /* Optimization to check if required orders are enabled early. */ > if (vma_is_anonymous(vma)) { > unsigned long mask = READ_ONCE(huge_anon_orders_always); > bool huge_enforce = !(tva_flags & TVA_ENFORCE_SYSFS); > bool has_madvise = vm_flags & VM_HUGEPAGE; > > /* > * if the user sets a sysfs mode of madvise and if > TVA_ENFORCE_SYSFS > * is not set, we don't bother checking whether the VMA > has VM_HUGEPAGE > * set. > */ > if (huge_enforce || has_madvise) > mask |= READ_ONCE(huge_anon_orders_madvise); > if (hugepage_global_always() || > ((has_madvise || huge_enforce) && > hugepage_global_enabled())) OMG is that ugly. -- Cheers, David / dhildenb