From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 3B3EB12C7FD for ; Mon, 16 Sep 2024 09:43:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726479830; cv=none; b=Cglmf1BXHHWYdOAsXPuuAEVM+Mz1aBGcOewrhMpQSCj6qKOwIhXlZR4xQhMUD46z6rlLNxbPxFl7eJeVo39SHSXrUH6ctuGZVjwBj1xjwXUlhWIAG3JRIUxo0tBZ85YbnBaCRsy8eb/ku6hZfVkrZcQO76whn0PNRmwLHu4QjBg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726479830; c=relaxed/simple; bh=UMfROnT2E/A1FyTsyqmypfmltizd/z8u5dLO1oXJNJo=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=R0KgWSH/jPELad8uP/U+Pt5aM4WN2DaSrRcYb8JMNY8/zT89NI7ziJIDdzf6aM9pCE1vbrACapeUojlAwkoOa4pJXhKWYgm3gvaZTyFKwZ1467p+cpzkWVg++aaMBlA21p2hWI1gbf+9ErRicFRCPGAcaolGH7hPP/ep5cnTfmM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5CEE911FB; Mon, 16 Sep 2024 02:44:16 -0700 (PDT) Received: from e116581.blr.arm.com (e116581.arm.com [10.162.42.11]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 747EE3F66E; Mon, 16 Sep 2024 02:43:38 -0700 (PDT) From: Dev Jain To: akpm@linux-foundation.org, david@redhat.com, willy@infradead.org, kirill.shutemov@linux.intel.com Cc: ryan.roberts@arm.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, cl@gentwo.org, vbabka@suse.cz, mhocko@suse.com, apopple@nvidia.com, dave.hansen@linux.intel.com, will@kernel.org, baohua@kernel.org, jack@suse.cz, mark.rutland@arm.com, hughd@google.com, aneesh.kumar@kernel.org, yang@os.amperecomputing.com, peterx@redhat.com, ioworker0@gmail.com, jglisse@google.com, wangkefeng.wang@huawei.com, ziy@nvidia.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Dev Jain Subject: [PATCH v4 0/2] Do not shatter hugezeropage on wp-fault Date: Mon, 16 Sep 2024 15:13:07 +0530 Message-Id: <20240916094309.1226908-1-dev.jain@arm.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit It was observed at [1] and [2] that the current kernel behaviour of shattering a hugezeropage is inconsistent and suboptimal. For a VMA with a THP allowable order, when we write-fault on it, the kernel installs a PMD-mapped THP. On the other hand, if we first get a read fault, we get a PMD pointing to the hugezeropage; subsequent write will trigger a write-protection fault, shattering the hugezeropage into one writable page, and all the other PTEs write-protected. The conclusion being, as compared to the case of a single write-fault, applications have to suffer 512 extra page faults if they were to use the VMA as such, plus we get the overhead of khugepaged trying to replace that area with a THP anyway. Instead, replace the hugezeropage with a THP on wp-fault. v3->v4: - Renames: pmd_thp_fault_alloc -> vma_alloc_anon_folio_pmd, map_pmd_thp -> map_anon_folio_pmd - Instead of passing around, compute haddr at various places, similar with gfp flags - Pass haddr to update_mmu_cache_pmd() instead of unaligned address - Do not pass vmf to map_anon_folio_pmd - Do declarations in reverse xmas tree order - Drop a new line which was introduced accidentally - Call __pmd_thp_fault_success_stats from map_anon_folio_pmd - Correctly return NULL from vma_alloc_anon_folio_pmd - Initialize pgtable to NULL in __do_huge_pmd_anonymous_page, to prevent freeing pgtable when not even allocated - Drop if conditions from map_anon_folio_pmd, let the caller handle that v2->v3: - Drop foliop and order parameters, prefix the thp functions with pmd_ - First allocate THP, then pgtable, not vice-versa - Move pgtable_trans_huge_deposit() from map_pmd_thp() to caller - Drop exposing functions in include/linux/huge_mm.h - Open code do_huge_zero_wp_pmd_locked() - Release folio in case of pmd change after taking the lock, or check_stable_address_space() returning VM_FAULT_SIGBUS - Drop uffd-wp preservation. Looking at page_table_check_pmd_flags(), preserving uffd-wp on a writable entry is invalid. Looking at mfill_atomic(), uffd_copy() is a null operation when pmd is marked uffd-wp. v1->v2: - Wrap do_huge_zero_wp_pmd_locked() around lock and unlock - Call thp_fault_alloc() before do_huge_zero_wp_pmd_locked() to avoid - calling sleeping function from spinlock context [1]: https://lore.kernel.org/all/3743d7e1-0b79-4eaf-82d5-d1ca29fe347d@arm.com/ [2]: https://lore.kernel.org/all/1cfae0c0-96a2-4308-9c62-f7a640520242@arm.com/ The patchset has been rebased on the mm-unstable branch. Dev Jain (2): mm: Abstract THP allocation mm: Allocate THP on hugezeropage wp-fault mm/huge_memory.c | 152 +++++++++++++++++++++++++++++++++-------------- 1 file changed, 109 insertions(+), 43 deletions(-) -- 2.30.2