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Received: from willy by casper.infradead.org with local (Exim 4.99.1 #2 (Red Hat Linux)) id 1wrn9W-00000005str-3Ftr; Thu, 06 Aug 2026 01:44:10 +0000 Date: Thu, 6 Aug 2026 02:44:10 +0100 From: Matthew Wilcox To: "Lorenzo Stoakes (ARM)" Cc: =?iso-8859-1?Q?C=E9dric?= Le Goater , Andrew Morton , linux-mm@kvack.org, Peter Xu , David Hildenbrand , Alex Williamson , Jason Gunthorpe , Zi Yan , stable@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/huge_memory: let special huge VMAs bypass the THP policy check Message-ID: References: <20260805055544.1568534-1-clg@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 5A49C40007 X-Rspamd-Server: rspam10 X-Rspam-User: X-Stat-Signature: srsr4yjcj7xxo57eck6rtubrxt1f877s X-HE-Tag: 1785980652-200856 X-HE-Meta: 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 J0IRxtmY himUodBct7v9nxBh15shnZupPJ84OLm6WD8s5qZFbv3rbNgXoPLu4BIO8TivxmVlPQ2UteIUSHYCPCltkIKV06nhy0XWrDpBqDJnfneWwNgGhBi64KITbWQdX8a/Dix+RWw+1ix3gFWCP+f9LA2zly/1D10R5Li/tqS24Dt4tmynr+4dxKbkZbAzY39Aquf/QGlhxB8VoE4kAuSRtiH1voqo/TiPG+W519jIIePhiJsYoEx6YhbVTfDwpo6w/JqUeSl3L2R4FqdTjGfv2V0bFVnD/z5JL0G9Y3wUcK/OyFgPI4wzzXiG9PVAUD3Ds6zTqeWGG Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Aug 05, 2026 at 11:41:46AM +0100, Lorenzo Stoakes (ARM) wrote: > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index abc65d608c23..5fa01364f089 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -111,6 +111,34 @@ static bool vma_is_special_huge(const struct vm_area_struct *vma) > return vma_test_any(vma, VMA_PFNMAP_BIT, VMA_MIXEDMAP_BIT); > } > > +static bool should_obey_thp_file_tunables(const struct vm_area_struct *vma, > + bool forced_collapse) > +{ > + if (forced_collapse) > + return false; > + VM_WARN_ON_ONCE(vma_is_anonymous(vma)); > + /* Huge PFN mappings allocate no folios so the policy doesn't apply. */ > + if (vma_test(vma, VMA_PFNMAP_BIT) && vma->vm_ops->huge_fault) > + return false; > + return true; > +} > + > +static bool can_thp_collapse_file(const struct vm_area_struct *vma, > + vm_flags_t vm_flags, bool forced_collapse) > +{ > + /* Override THP tunables? */ > + if (!should_obey_thp_file_tunables(vma, forced_collapse)) > + return true; > + /* THP=always? */ > + if (hugepage_global_always()) > + return true; > + /* THP=madvise? */ > + if (!hugepage_global_enabled()) > + return false; > + /* Has VMA had madvise(..., MADV_HUGEPAGE) applied to it? */ > + return vm_flags & VM_HUGEPAGE; > +} > + > unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, > vm_flags_t vm_flags, > enum tva_type type, > @@ -188,9 +216,7 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, > * Enforce THP collapse requirements as necessary. Anonymous vmas > * were already handled in thp_vma_allowable_orders(). > */ > - if (!forced_collapse && > - (!hugepage_global_enabled() || (!(vm_flags & VM_HUGEPAGE) && > - !hugepage_global_always()))) > + if (!can_thp_collapse_file(vma, vm_flags, forced_collapse)) > return 0; > > /* I think 'thp_' in all of this is confusing. DAX isn't THPs. PFNMAPs aren't THPa. There's other reasons to implement huge_fault that aren't THPs. Can we rename all of this to drop the 'thp_' string, starting with thp_vma_allowable_order()?