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 13F68419304; Thu, 27 Aug 2026 19:56:14 +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=1787860577; cv=none; b=hWwJm+j+t7GWY3JuAROFnMkB7q//4tNv9Ejwfq95APBZKBOlXpSumiiv2j7K083SeRiGrHagrqKa5HrIDZWk4tzU8bta39SrRhM2Btf47dg6xsDCemvOtBrciFmYb+YgCxUEK/s1Y2sM80osrdEjrt5rNCSNShzx1cWckemaucE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787860577; c=relaxed/simple; bh=h4rmM/F/oNz34A4BdZhkckrXP4Zm0dW0AF2/rRuAMLo=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:To:Cc; b=X0ck5E3c6anZUm5r6VnvsU0cv4a1Pv8Bg7UNFmzOYSinfvKuPRP3G9E5NIB0FmYTjIlmyabokUfigbAOJnRcVuGSYka2m91HA63oRZOkXDgN/6l/vglP1HmJrhpDtjRSRib4DlljPy0P+ASszH2Ukhrf2TvMhrx1Otc4H+25Jcc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CqvpX0jc; 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="CqvpX0jc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 085971F000E9; Thu, 27 Aug 2026 19:56:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787860573; bh=yXmT+LEQ61WRjbUCLimpBHndS1SBsTfjBnnvx00VCQw=; h=From:Date:Subject:To:Cc; b=CqvpX0jc2vi3EeZtwyvsdALHmWqfFBu9TPA54ePXXCKBye6bDmz608MGBIBKYgAea De8XOGagcpUghO118Jj9V2yMEVxL8+IQ5ZNqxci8Nziv1q4a41XWqFgph53l6G1N7k fMJKr0xl78xlHmyChj/90LdR1VE6rY64PV9OpdDOFl6AJTPKVuNf7aIQaO6vtFXOaM thIj631uIBq4fE3s9yfK/y4uEylczFepyStGQZKY5ldBIW1rqYC+Rb8cl/GQjYodf7 0CZTMe3mJskgA6MAxIbO5GlqZs4lMIjkoZV3lQs1jpszzFm05Q83jtbDzYMqpXlG8+ ST1sDQ74gWVrA== From: "Lorenzo Stoakes (ARM)" Date: Thu, 27 Aug 2026 20:55:57 +0100 Subject: [PATCH] mm/huge_memory: bypass THP tuneables for huge pfnmap mappings Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260827-hugepfn-allowable-orders-v1-1-94819c8807c8@kernel.org> X-B4-Tracking: v=1; b=H4sIAAAAAAAC/x3MSQqAMAxA0atI1ga04oBXERdVEw2UVlIcQLy7x eVb/P9AJBWK0GcPKJ0SJfiEMs9g3qxfCWVJBlOYpuhMi9ux0s4erXPhspMjDLqQRmSuTMVdzXP dQsp3JZb7Xw/j+36QQrp/agAAAA== X-Change-ID: 20260827-hugepfn-allowable-orders-ff323f85fc57 To: Andrew Morton , David Hildenbrand , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Peter Xu , Jason Gunthorpe Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Cedric Le Goater , Saravanan D , stable@vger.kernel.org, "Lorenzo Stoakes (ARM)" X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=openpgp-sha256; l=5776; i=ljs@kernel.org; h=from:subject:message-id; bh=h4rmM/F/oNz34A4BdZhkckrXP4Zm0dW0AF2/rRuAMLo=; b=owGbwMvMwCV2fu7ZrsZH9SKMp9WSGLImTAuz/G8TaGmjtc9Fcv2ptndfEyxcpJdNqlnWvOqg4 E6Lq63rO0pZGMS4GGTFFFmefxHfHyQSNq/zgr8bzBxWJpAhDFycAjCR8+WMDK9q7bq0zwk+mLRt Scm07w4XfIN0g6Lru75HX1r/bFFhby0jw65tKb5bfFQO3lnZZvpMdyfz532iBSL+WdrhHqc2T3q awA8A X-Developer-Key: i=ljs@kernel.org; a=openpgp; fpr=E7F417BF5214569E89D04F46CF9DCD8A81E27F14 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; if (vma_is_temporary_stack(vma)) return 0; --- base-commit: 234e77148199ae43b83a0a03a3f481e03460a286 change-id: 20260827-hugepfn-allowable-orders-ff323f85fc57 Best regards, -- Lorenzo Stoakes (ARM)