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[2003:d8:2f2c:1e00:1e1e:7a32:e798:6457]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a561a3ce6bsm2085920f8f.49.2025.06.12.07.09.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Jun 2025 07:09:28 -0700 (PDT) Message-ID: Date: Thu, 12 Jun 2025 16:09:27 +0200 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: Lorenzo Stoakes Cc: Baolin Wang , 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> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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>> +/* 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); >> + >> + /* Disallow orders that are set to NEVER directly ... */ >> + orders &= ~never; >> + >> + /* ... or through inheritance (global == NEVER). */ >> + if (!hugepage_global_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; > > This implicitly does a & mask as per suggested previous version, which I think > is correct but worth pointing out. Yes. > >> + >> + if (!(vm_flags & VM_HUGEPAGE)) { > > Don't love this sort of mega negation here. I read this as _does_ have huge > page... Well, it's very common to do that, but not objecting to something that is clearer ;) I assume you spotted the if (!(tva_flags & TVA_ENFORCE_SYSFS)) :P if (vm_flags & VM_HUGEPAGE) return orders; Would have been easier. > >> + /* Disallow orders that are set to MADVISE directly ... */ >> + orders &= ~madvise; >> + >> + /* ... or through inheritance (global == MADVISE). */ >> + if (!hugepage_global_always()) >> + orders &= ~inherit; > > I hate this implicit 'not hugepage global always so this means either never or > madvise and since we cleared orders for never this means madvise' mental > gymnastics required here. > > Yeah I feel this is a bridge too far, we're getting into double negation and I > think that's more confusiong. Same here ... I think we should just have hugepage_global_madvise(). :) > > >> + } > > 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(); Can we just have hugepage_global_never/disabled() to use instead? > > /* 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); > > return orders & always; > } > > What do you think? With the fixup, it would work for me. No magical "mask" variables :D > > >> + return orders; >> +} >> + >> /** >> * thp_vma_allowable_orders - determine hugepage orders that are allowed for vma >> * @vma: the vm area to check >> @@ -287,16 +323,8 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma, >> unsigned long orders) >> { >> /* Optimization to check if required orders are enabled early. */ >> - if ((tva_flags & TVA_ENFORCE_SYSFS) && vma_is_anonymous(vma)) { >> - unsigned long mask = READ_ONCE(huge_anon_orders_always); >> - >> - if (vm_flags & VM_HUGEPAGE) >> - mask |= READ_ONCE(huge_anon_orders_madvise); >> - if (hugepage_global_always() || >> - ((vm_flags & VM_HUGEPAGE) && hugepage_global_enabled())) >> - mask |= READ_ONCE(huge_anon_orders_inherit); >> - >> - orders &= mask; >> + if (vma_is_anonymous(vma)) { >> + orders = __thp_mask_anon_orders(vm_flags, tva_flags, orders); >> if (!orders) >> return 0; > > I pointed out to Baolin that __thp_vma_allowable_orders() handles the orders == > 0 case almost immediately so there's no need to do this, it just makes the code > noisier. The reason we added it in the first place was to not do the (expensive) function call. -- Cheers, David / dhildenb