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[2003:d8:2f2c:1e00:1e1e:7a32:e798:6457]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a561a3cd3esm1333342f8f.63.2025.06.12.01.51.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Jun 2025 01:51:18 -0700 (PDT) Message-ID: <953596b2-8749-493d-97eb-a5d8995d9ef8@redhat.com> Date: Thu, 12 Jun 2025 10:51:17 +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: Baolin Wang , akpm@linux-foundation.org, hughd@google.com Cc: lorenzo.stoakes@oracle.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> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 9155FC0007 X-Stat-Signature: uptbz5gwg9mnjyajw4etbpxwe7ff6po3 X-Rspam-User: X-HE-Tag: 1749718283-647043 X-HE-Meta: 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 f9rQVBxu 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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 12.06.25 09:51, Baolin Wang wrote: > > > On 2025/6/11 20:34, David Hildenbrand wrote: >> On 05.06.25 10:00, Baolin Wang wrote: >>> The MADV_COLLAPSE will ignore the system-wide Anon THP sysfs settings, >>> which >>> means that even though we have disabled the Anon THP configuration, >>> MADV_COLLAPSE >>> will still attempt to collapse into a Anon THP. This violates the rule >>> we have >>> agreed upon: never means never. >>> >>> Another rule for madvise, referring to David's suggestion: “allowing >>> for collapsing >>> in a VM without VM_HUGEPAGE in the "madvise" mode would be fine". >>> >>> To address this issue, should check whether the Anon THP configuration >>> is disabled >>> in thp_vma_allowable_orders(), even when the TVA_ENFORCE_SYSFS flag is >>> set. >>> >>> In summary, the current strategy is: >>> >>> 1. If always & orders == 0, and madvise & orders == 0, and >>> hugepage_global_enabled() == false >>> (global THP settings are not enabled), it means mTHP of that orders >>> are prohibited >>> from being used, then madvise_collapse() is forbidden for that orders. >>> >>> 2. If always & orders == 0, and madvise & orders == 0, and >>> hugepage_global_enabled() == true >>> (global THP settings are enabled), and inherit & orders == 0, it means >>> mTHP of that >>> orders are still prohibited from being used, thus madvise_collapse() >>> is not allowed >>> for that orders. >>> >>> Reviewed-by: Zi Yan >>> Signed-off-by: Baolin Wang >>> --- >>>   include/linux/huge_mm.h | 23 +++++++++++++++++++---- >>>   1 file changed, 19 insertions(+), 4 deletions(-) >>> >>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >>> index 2f190c90192d..199ddc9f04a1 100644 >>> --- a/include/linux/huge_mm.h >>> +++ b/include/linux/huge_mm.h >>> @@ -287,20 +287,35 @@ 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 (vma_is_anonymous(vma)) { >>> +        unsigned long always = READ_ONCE(huge_anon_orders_always); >>> +        unsigned long madvise = READ_ONCE(huge_anon_orders_madvise); >>> +        unsigned long inherit = READ_ONCE(huge_anon_orders_inherit); >>> +        unsigned long mask = always | madvise; >>> + >>> +        /* >>> +         * If the system-wide THP/mTHP sysfs settings are disabled, >>> +         * then we should never allow hugepages. >> > +         */> +        if (!(mask & orders) && >> !(hugepage_global_enabled() && (inherit & orders))) >>> +            return 0; >> >> I'm still trying to digest that. Isn't there a way for us to work with >> the orders, >> essentially masking off all orders that are forbidden globally. Similar >> to below, if !orders, then return 0? >> /* Orders disabled directly. */ >> orders &= ~TODO; >> /* Orders disabled by inheriting from the global toggle. */ >> if (!hugepage_global_enabled()) >>     orders &= ~READ_ONCE(huge_anon_orders_inherit); >> >> TODO is probably a -1ULL and then clearing always/madvise/inherit. Could >> add a simple helper for that >> >> huge_anon_orders_never > > I followed Lorenzo's suggestion to simplify the logic. Does that look > more readable? > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index 2f190c90192d..3087ac7631e0 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -265,6 +265,43 @@ unsigned long __thp_vma_allowable_orders(struct > vm_area_struct *vma, > unsigned long tva_flags, > unsigned long orders); > > +/* 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) > +{ > + unsigned long always = READ_ONCE(huge_anon_orders_always); > + unsigned long madvise = READ_ONCE(huge_anon_orders_madvise); > + unsigned long inherit = READ_ONCE(huge_anon_orders_inherit); > + bool inherit_enabled = hugepage_global_enabled(); > + bool has_madvise = vm_flags & VM_HUGEPAGE; > + unsigned long mask = always | madvise; > + > + mask = always | madvise; > + if (inherit_enabled) > + mask |= inherit; > + > + /* All set to/inherit NEVER - never means never globally, abort. */ > + if (!(mask & orders)) > + return 0; Still confusing. I am not sure if we would properly catch when someone specifies e.g., 2M and 1M, while we only have 2M disabled. I would rewrite the function to only ever substract from "orders". ... /* Disallow orders that are set to NEVER directly ... */ order &= (always | madvise | inherit); /* ... or through inheritance. */ 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 (!orders || !(tva_flags & TVA_ENFORCE_SYSFS)) return orders; > + > + /* > + * 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; > + > + mask = always; > + if (has_madvise) > + mask |= madvise; > + if (hugepage_global_always() || (has_madvise && inherit_enabled)) > + mask |= inherit; Similarly, this can maybe become (not 100% sure if I got it right, the condition above is confusing) if (!has_madvise) { /* * Without VM_HUGEPAGE, only allow orders that are set to * ALWAYS directly ... */ order &= (always | inherit); /* ... or through inheritance. */ if (!hugepage_global_always()) orders &= ~inherit; } -- Cheers, David / dhildenb