From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 267DD391E4E; Thu, 6 Aug 2026 16:19:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786033172; cv=none; b=P0yTxLYqntU2GV0UoMFohMNunr7T2+g+1k7DR6HMYaCOKAckB+D10QBx6DAWsnQ2TKb3VAcpSWCzPNYPeu2ycCMCHIr7mZEk4V29M8AGbjlCEmV6pwMKEbBlUGiyWpIrrrJMR8GTYvhWsfnqQWxcEhenE56eO2j4kRe4A2M12vI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786033172; c=relaxed/simple; bh=vrZyDYEM1OcMEibhu6RE+3IJgS857AmWUKRmjA7ctMA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=C5cq8IcsKMH5pbK5hsDhs0+T/MXyYoQJNNAkxN1eQYOncKvjJldRFGCcH8m64PTou+aSbGrptvgplUmJLg6WndqK7shENOIbsmOKsHEY6HZiRye0Qmv8oL0H32sjLj7eSu1osam6G4bILWA2q/UhSt/gUVjrrKqTie5lY8lrMZY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HVMqoUR7; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="HVMqoUR7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DDBAD1F000E9; Thu, 6 Aug 2026 16:19:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786033170; bh=0QPBNhSSVOZyz+OIXJH4NAAN8xAfuyeE6tVMmrlOwqw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=HVMqoUR7jyI1x5GfJqW6ghPpKJBZUnJkWRTqjmafA81stRol0LfIpVqXZQCSUO1nx lnUSE4m8vB8xg83HDUO8ji0CLXBY0BeefD+wYHjoP1o8MaL6zk9tleDmSpV9N4+0Wr +4ApPrT5JR/1Sw2EUM8PP0SsVr0y7+CcPjx2WuvqmcJ0LsJC2rPBLEtnuRUlRx5fd5 Bcb4G08Aysueg4NJLOHWJXnOeR8PBEvZHTqAPCMGafO+h2XqqdCGKR9d533JJefeVT GMO/EZv041ylqOCF0X7SWXK+dj3ebQB+iihJu4Yy/Tk4wKpu0Qa29oBaKSqWbBUlKf 7GSAPRr8vTdIg== Message-ID: <0bd6d355-e6d9-4f5a-b101-9a041c2a2436@kernel.org> Date: Thu, 6 Aug 2026 18:19:25 +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] mm/huge_memory: let special huge VMAs bypass the THP policy check To: "Lorenzo Stoakes (ARM)" , =?UTF-8?Q?C=C3=A9dric_Le_Goater?= Cc: Andrew Morton , linux-mm@kvack.org, Peter Xu , Alex Williamson , Jason Gunthorpe , Zi Yan , stable@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260805055544.1568534-1-clg@redhat.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit > From d6537260722c8741586e6295c8eea68d06087efa Mon Sep 17 00:00:00 2001 > From: "Lorenzo Stoakes (ARM)" > Date: Wed, 5 Aug 2026 11:35:13 +0100 > Subject: [PATCH] ideas > > --- > mm/huge_memory.c | 32 +++++++++++++++++++++++++++++--- > 1 file changed, 29 insertions(+), 3 deletions(-) > > 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; > +} If that's sufficient, then this is is the better direction. > +> +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 played a bit with that and came up with the following. Not quite happy about it, just for your inspiration on naming and what to split out. diff --git a/mm/huge_memory.c b/mm/huge_memory.c index a00df56a68b57..8ba77608959d4 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -111,6 +111,54 @@ 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 file_vma_honors_thp_toggles(struct vm_area_struct *vma, + enum tva_type type) +{ + const bool forced_collapse = type == TVA_FORCED_COLLAPSE; + + if (forced_collapse) + return false; + /* Huge PFN mappings allocate no folios so the policy doesn't apply. */ + return !(vma_test(vma, VMA_PFNMAP_BIT) && vma->vm_ops->huge_fault); +} + +static bool vma_thp_toggles_enabled(struct vm_area_struct *vma, + vm_flags_t vm_flags) +{ + /* THP=always? */ + if (hugepage_global_always()) + return true; + /* THP=madvise and actually advised? */ + return hugepage_global_enabled() && vm_flags & VM_HUGEPAGE; +} + +static bool file_vma_forces_order_0(struct vm_area_struct *vma, + vm_flags_t vm_flags, enum tva_type type) +{ + const bool in_pf = type == TVA_PAGEFAULT; + const bool smaps = type == TVA_SMAPS; + + /* + * Enforce THP collapse requirements as necessary. Anonymous vmas + * were already handled in thp_vma_allowable_orders(). + */ + + if (file_vma_honors_thp_toggles(vma, type) && + !vma_thp_toggles_enabled(vma, vm_flags)) + return true; + + /* + * Trust that ->huge_fault() handlers know what they are doing + * in fault path. + */ + if (((in_pf || smaps)) && vma->vm_ops->huge_fault) + return false; + /* Only regular file is valid in collapse path */ + if (((!in_pf || smaps)) && file_thp_enabled(vma)) + return false; + return true; +} + unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, vm_flags_t vm_flags, enum tva_type type, @@ -183,27 +231,8 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, vma, vma_start_pgoff(vma), 0, forced_collapse); - if (!vma_is_anonymous(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()))) - return 0; - - /* - * Trust that ->huge_fault() handlers know what they are doing - * in fault path. - */ - if (((in_pf || smaps)) && vma->vm_ops->huge_fault) - return orders; - /* Only regular file is valid in collapse path */ - if (((!in_pf || smaps)) && file_thp_enabled(vma)) - return orders; - return 0; - } + if (!vma_is_anonymous(vma)) + return __file_vma_forces_order_0(vma, vm_flags, type) ? 0 : orders; if (vma_is_temporary_stack(vma)) return 0; -- Cheers, David