From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 063F6C79FA1 for ; Mon, 7 Sep 2026 16:17:45 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DF94E6B008C; Mon, 7 Sep 2026 12:17:43 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DAA676B0092; Mon, 7 Sep 2026 12:17:43 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CE80B6B009D; Mon, 7 Sep 2026 12:17:43 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 6C81C6B008C for ; Mon, 7 Sep 2026 12:17:43 -0400 (EDT) Received: from smtpin09.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id DF311401D7 for ; Mon, 7 Sep 2026 16:17:42 +0000 (UTC) X-FDA: 85187471964.09.5FDD7CC Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf12.hostedemail.com (Postfix) with ESMTP id 555AF40006 for ; Mon, 7 Sep 2026 16:17:41 +0000 (UTC) Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=chjSiu0k; spf=pass (imf12.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1788797861; b=I6Lkabo5MAl2GVDmu9TDPJztw8Z1uI8BpPe5Ur0QyTu7q/Hxp9qEZ6pGKeFbQKdJ1sqi1z FtbZwaRQNqi8ok74A6y9hklX06/Z7WCXJYtM4eKbQJ4rtJa5C69/BlvJVTzk85v73ClwEa ndut5DepmEOIx3IU5FUZL9Ig1rtRbwk= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=chjSiu0k; spf=pass (imf12.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1788797861; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=wOnQahPO1TmCL6FmC3Riu7SZQYrSuY8UOh5mIJltyRE=; b=Kgiyys9cUPAGWTF1KP8RsgeHquWLhuypktner+IbIaHvGLdT0M72HVn9bBOU0lCDIgBt/l iN9HM6JeM7dfaApsayucFvrM4mhlNg1iCqRbv5QKDK8biUv0iV3ZzgmuJuntN7f7rog5Hv yWA4VjormAzE3jukqerIfMGoHeb/NPs= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id DEE7D601DB; Mon, 7 Sep 2026 16:17:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 65D921F00A3A; Mon, 7 Sep 2026 16:17:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788797860; bh=wOnQahPO1TmCL6FmC3Riu7SZQYrSuY8UOh5mIJltyRE=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=chjSiu0kxNy55FySd80YLuWpGKduvYPpWOIeXBDAEDtKqnVBNh9d2zpIacBhCSdaA /hPjIqOuSUHj8c/P9fQmZl5QsN4WOnfiIOfKBSlpTDf98LalsExTWUCBri/U/G11Qu 463UFNmJOoS1/LOyoX+MydBYhJ4deFChj18UBUl7lXOC4G9EfqkcCO0FWNUFnMgVSu ZJ0dq8yg+/MGoN7WleKNCrwoFHxPeyLQn9DKBpOtPSgfQA6XKTE7mNpQtFaKmgn8pj cXgDuC+tRseK5NaxjJcE836EtT/y3wIWapSvHcDps3dvye1fYFKYf3q119INcb4rPb /Z9QHNIdzdHYA== Date: Mon, 7 Sep 2026 17:17:33 +0100 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Peter Xu , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Cedric Le Goater , Saravanan D , stable@vger.kernel.org Subject: Re: [PATCH] mm/huge_memory: bypass THP tuneables for huge pfnmap mappings Message-ID: References: <20260827-hugepfn-allowable-orders-v1-1-94819c8807c8@kernel.org> <034a2687-3551-485a-a382-e7e77aa3919b@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <034a2687-3551-485a-a382-e7e77aa3919b@kernel.org> X-Rspam-User: X-Stat-Signature: qdouu6cka96jiye1iu1dkagj4kni1z7p X-Rspamd-Queue-Id: 555AF40006 X-Rspamd-Server: rspam06 X-HE-Tag: 1788797861-119241 X-HE-Meta: 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 U6ZaP6Li e6aMGMSYUIaolNl9VNB62rCzBh7VnlELwyyQSEM3Bid4ZxZ7iz1CpZ4AkPlOP597uEmEZH+4ZWCPODPZ1lO8p/jYeVZ50ZdY3lMZARU4cxJ3nh4j9zJHfcSZI/BMccXjwHSMZgGqQUMyyFvKSJbzsjRERnHNvUHjk6/G2zPJTITm0ea9OK8DjviVDoX4TlSNa1G2d+iaLj8rdx993csVfsOAonvw2w7rFEV8jTnLCo1kRiogHM4FEo+RkHsX4kiWxXPRlpFLvBocDIQASiyYiz5nmOz6AEGTRTG04aN3OM8OQbiqH0EgWtmZEV2dCRzHIwNvKw4VQB2xvlazIWnVUfnV+/jLdHbqeFM+Y Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Sep 07, 2026 at 06:14:14PM +0200, David Hildenbrand (Arm) wrote: > On 8/27/26 21:55, Lorenzo Stoakes (ARM) wrote: > > The sysfs THP tuneables at /sys/kernel/mm/transparent_huge_pages/ rather > > confusingly only control the behaviour of THP in some instances. > > > > They are not applicable to MADV_COLLAPSE operations, nor to DAX mappings. > > > > Long-term, THP is predicated upon compaction being able to obtain large > > folios to populate THP ranges. > > > > However, vm_normal_folio() returns NULL for PFN map mappings, thus their > > reference count is maintained by the driver, not core mm. > > > > As a consequence, the folios are not subject to reclaim nor compaction, so > > are not truly part of the THP mechanism at all. > > > > However, since commit 5dd40721f147 ("mm: allow THP orders for PFNMAPs") > > introduced the ability to establish huge PFN maps, they have been subject > > to THP tuneables. > > > > This is incorrect - if a huge PFN map is available (defined by > > vma->vm_ops->huge_fault being non-NULL for a VMA_PFNMAP_BIT VMA), then it > > should be mapped huge upon fault-in. > > > > Correct this by explicitly checking for this while ensuring that smaps > > continues to accurately report THPeligible statistics. > > > > While here, abstract the entire file-backed THP check in > > vma_can_map_huge_file(), with sensible separation of logic into helper > > functions. > > > > Note that drm_gem_shmem_mmap() and panthor_gem_mmap() establish huge PFN > > maps of shmem folios, however they are marked unevictable in > > drm_gem_get_pages(), and in any case would fail the reference check in > > __remove_mapping() even if they weren't. > > > > Failing to map huge PFN maps has resulted in significant real-world > > performance degradation, see links for details. > > > > Reported-by: Cedric Le Goater > > Closes: https://lore.kernel.org/linux-mm/20260805055544.1568534-1-clg@redhat.com/ > > Reported-by: Saravanan D > > Closes: https://lore.kernel.org/linux-mm/20260821070520.25759-1-saravanand@crusoe.ai/ > > Fixes: 5dd40721f147 ("mm: allow THP orders for PFNMAPs") > > Cc: stable@vger.kernel.org > > Signed-off-by: Lorenzo Stoakes (ARM) > > --- > > mm/huge_memory.c | 86 +++++++++++++++++++++++++++++++++++++++++--------------- > > 1 file changed, 64 insertions(+), 22 deletions(-) > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index afbb5974bd22..4bf7b670586d 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -92,7 +92,7 @@ unsigned long huge_anon_orders_madvise __read_mostly; > > unsigned long huge_anon_orders_inherit __read_mostly; > > static bool anon_orders_configured __initdata; > > > > -static inline bool file_thp_enabled(struct vm_area_struct *vma) > > +static inline bool file_thp_enabled(const struct vm_area_struct *vma) > > { > > struct inode *inode; > > > > @@ -118,6 +118,67 @@ 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 vma_bypass_thp_tuneables_file(const struct vm_area_struct *vma, > > + enum tva_type type) > > +{ > > + const bool has_huge_fault = vma->vm_ops->huge_fault; > > + > > + /* MADV_COLLAPSE ignores tuneables. */ > > + if (type == TVA_FORCED_COLLAPSE) > > + return true; > > + /* Huge PFN mappings are uncompactable so the policy doesn't apply. */ > > + if (vma_test(vma, VMA_PFNMAP_BIT) && has_huge_fault) > > + return true; > > + return false; > > +} > > + > > +static bool vma_thp_tuneables_allow_file(vm_flags_t vm_flags) > > +{ > > + /* THP=always? */ > > + if (hugepage_global_always()) > > + return true; > > + /* THP=madvise and marked MADV_HUGEPAGE? */ > > + if (hugepage_global_enabled() && (vm_flags & VM_HUGEPAGE)) > > + return true; > > + return false; > > +} > > + > > +static bool vma_check_thp_tuneables_file(const struct vm_area_struct *vma, > > + vm_flags_t vm_flags, enum tva_type type) > > +{ > > + return vma_bypass_thp_tuneables_file(vma, type) || > > + vma_thp_tuneables_allow_file(vm_flags); > > +} > > + > > +static bool vma_can_map_huge_file(const struct vm_area_struct *vma, > > + vm_flags_t vm_flags, enum tva_type type) > > +{ > > + const bool has_huge_fault = vma->vm_ops->huge_fault; > > + > > + /* > > + * Enforce THP collapse requirements as necessary. Anonymous vmas > > + * were already handled in thp_vma_allowable_orders(). > > + */ > > + if (!vma_check_thp_tuneables_file(vma, vm_flags, type)) > > + return false; > > + > > + switch (type) { > > + case TVA_PAGEFAULT: > > + /* > > + * Trust that ->huge_fault() handlers know what they are doing > > + * in fault path. > > + */ > > + return has_huge_fault; > > + case TVA_SMAPS: > > + if (has_huge_fault) > > + return true; > > + fallthrough; > > + default: > > + /* Only regular file is valid in collapse path. */ > > + return file_thp_enabled(vma); > > + } > > +} > > + > > unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, > > vm_flags_t vm_flags, > > enum tva_type type, > > @@ -190,27 +251,8 @@ 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 vma_can_map_huge_file(vma, vm_flags, type) ? orders : 0; > > I don't have the time to find out how these functions ended up being named, I'll > have to trust that it will be alright. :-O > > Adding to what Zi say, vma_can_map_huge_file is also confusing, no? Yeah I agree, I had a model in my head as to why it was an OK name then when Zi raised it I realised that my naming scheme was, in fact, terrible :) > > are we mapping a huge file? :) Lol... hugetlb maybe? HW poision too? Perhaps? OK you've only been back for a day I should stop using these swear words :P > > -- > Cheers, > > David -- Cheers, Lorenzo