From patchwork Tue Oct 8 06:17:44 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dev Jain X-Patchwork-Id: 13825673 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2917DCED26B for ; Tue, 8 Oct 2024 06:19:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-Type: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References:List-Owner; bh=tHPHwP7Tp8k/32rfrSKz2E1ogPbCqXJq9itbEwMJ8mo=; b=3wXig2mDl/rPzZXeYhLOM2zaNI XoHMGaCt+8LXLcTpqgn4IgDo7VFlwFQ8RHNmGDUBEl2R4Hsup0RXngyhCtdED4knPoi4EKmRsp3O6 9tXrSmKZ4XxFNLz9IwWdv1hnkLU3IJZtDVlVjwbqoJwgh63ARNQhCmpzt4UrScDPNjY4eOaTuMV+l V0qHjaayBAGUWWmjnM8pxD/iVmbY/GJOGChMPHdTCdAWGHXmlDRimoMKHfXD6t5STMk7UxQAvK1OH /IUYLXbIsYx17A0+OPTC/aComaK1my017OE2nGrULterRodaLGSKEoK+YCf+wsjdGlp1Gr1nK94Ol EaGYJc0w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1sy3ZH-00000004d8M-2Olv; Tue, 08 Oct 2024 06:19:35 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1sy3Xv-00000004cxF-3Rie for linux-arm-kernel@lists.infradead.org; Tue, 08 Oct 2024 06:18:14 +0000 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 175A7DA7; Mon, 7 Oct 2024 23:18:36 -0700 (PDT) Received: from e116581.blr.arm.com (e116581.arm.com [10.162.43.142]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 77E8F3F73F; Mon, 7 Oct 2024 23:17:57 -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-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Dev Jain Subject: [PATCH v7 0/2] Do not shatter hugezeropage on wp-fault Date: Tue, 8 Oct 2024 11:47:44 +0530 Message-Id: <20241008061746.285961-1-dev.jain@arm.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20241007_231811_951779_E2EC0057 X-CRM114-Status: GOOD ( 13.45 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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. [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. v6->v7: Align function parameters in the second line by two tabs v5->v6: - More goto ommissions, remove build warning for !CONFIG_NUMA v4->v5: - Directly return VM_FAULT_FALLBACK in case of !folio 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 Dev Jain (2): mm: Abstract THP allocation mm: Allocate THP on hugezeropage wp-fault mm/huge_memory.c | 139 +++++++++++++++++++++++++++++++++-------------- 1 file changed, 97 insertions(+), 42 deletions(-)