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 63A0451FCBD; Mon, 7 Sep 2026 17:33:23 +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=1788802404; cv=none; b=YQEdVLNljhAhVId3o0kPVEpuhBSuh+ZsSfiIIW+WHprI1Xok6fPClMXGG6TEwAN8hSU778H0CXHBIuqJYsMyYAxL1Ufwo/j9kmJw5YN0ZWWbufIlJVhQIQxj2amFGh7dRzpNt0XV88SO1qwSyEhf+Rjzos+YM4Yh8yK/MbOqHTg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788802404; c=relaxed/simple; bh=EbkfQrduiBo4n56BhART5zdrKo//tuFGC85yYHYENTM=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:To:Cc; b=rZ1PrwF2qarN6a0DfplUeZP6YPmHLJ7btyNoj5LE7+jye/SciZxRMuVWLENMmahwmOrlcsqgYSwJCXFcKvWel3RW9hk/5V8iabiJ5H7S+tT/hbkGyROyG0LzyHq+GwdNPWTQLtXELqb58+mBdsob943a9qeVoI0tiTAjm5Z8Rh4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FSB8dMCs; 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="FSB8dMCs" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 169781F00A3A; Mon, 7 Sep 2026 17:33:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788802403; bh=yrolGENT0USe5XNn+JkmDXEFy0r+GXBioZLVApy6mzs=; h=From:Date:Subject:To:Cc; b=FSB8dMCsmsGaYWSPpFiysguN/Ap562nxVy2Bo53ltfSz/PX0oLvPdNinem2ITEKaL jBUs4aLDVa+eCCH64gKFzT3+/G3lvjDhQZgTfR+enAZQsN9LIJ0/zr+r3VU6x20Mvh oVpwgk67cKT/3hBiLKWfdqn3M0phYLFBAvc1gO2kCxk8MweKJarGm6ISxO8qpr0e9z 9B4hL7Ccy95egipxuda1eDFdD79eAn0eJX/TL6ALyHU7Ac44u0AvNxEIIlrWvVHCa+ 3UncHhyDGkyWgZicB8FJ3UGXTEv222ss6/lvdvFIH25xJ4ysY0XVOdZ51qc6gsbzcA reCd5naIPLnzQ== From: "Lorenzo Stoakes (ARM)" Date: Mon, 07 Sep 2026 18:33:13 +0100 Subject: [PATCH v2] 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: <20260907-hugepfn-allowable-orders-v2-1-b89728339148@kernel.org> X-B4-Tracking: v=1; b=H4sIAAAAAAAC/42NQQ6CMBBFr0Jm7RhaRAor72FYYJlCY9OSqaKG9 O5WTuDyveS/v0EkthShKzZgWm20wWeQhwL0PPiJ0I6ZQZbyXCrZ4PycaDEeB+fCa7g5wsAjcUR jKlkZVRtdN5DnC5Ox7z197TPPNj4Cf/anVfzsH9FVoMD2pESrlSobrS53Yk/uGHiCPqX0Be7yW mHBAAAA 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, SJ Park , "Lorenzo Stoakes (ARM)" X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=openpgp-sha256; l=6275; i=ljs@kernel.org; h=from:subject:message-id; bh=EbkfQrduiBo4n56BhART5zdrKo//tuFGC85yYHYENTM=; b=owGbwMvMwCV2fu7ZrsZH9SKMp9WSGLLmfY3j47gkEcCUGts4/8mlzNPL4s5OcJq5U6/UQ3Gp5 +Hi3zqcHaUsDGJcDLJiiizPv4jvDxIJm9d5wd8NZg4rE8gQBi5OAZjI/J2MDI0GE1X1mvW7j7pM fM7ImDxzo8bHe+EWRVyrTdYu9p2wn4uR4a6+zyYj66B4oRvd/OfzjwvNOr560dQY77OFKWk6ifp 83AA= 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 Reviewed-by: Baolin Wang Reviewed-by: SJ Park Tested-by: Saravanan D Tested-by: Lance Yang Reviewed-by: Zi Yan Signed-off-by: Lorenzo Stoakes (ARM) --- v2: - Added tags thanks everybody! - Updated to use vma_file_*() naming as per Zi. - Also updated vma_can_map_huge_file() to vma_file_can_map_huge() as per David. v1: https://lore.kernel.org/r/20260827-hugepfn-allowable-orders-v1-1-94819c8807c8@kernel.org --- 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..75c204af40cb 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_file_bypass_thp_tuneables(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_file_allow_thp_tuneables(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_file_check_thp_tuneables(const struct vm_area_struct *vma, + vm_flags_t vm_flags, enum tva_type type) +{ + return vma_file_bypass_thp_tuneables(vma, type) || + vma_file_allow_thp_tuneables(vm_flags); +} + +static bool vma_file_can_map_huge(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_file_check_thp_tuneables(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_file_can_map_huge(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)