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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9CBF0C433FE for ; Tue, 18 Oct 2022 00:46:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230123AbiJRAqr (ORCPT ); Mon, 17 Oct 2022 20:46:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60498 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229848AbiJRAqd (ORCPT ); Mon, 17 Oct 2022 20:46:33 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 645911A3B1 for ; Mon, 17 Oct 2022 17:46:31 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 5B2256131C for ; Tue, 18 Oct 2022 00:46:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AF215C433D7; Tue, 18 Oct 2022 00:46:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1666053989; bh=r6K7hrtEPetH7gKjRYN3jo/E1xb20pJ+S7O8IVVmnAs=; h=Date:To:From:Subject:From; b=C0k0TRqYy3ahgP8yJFUdsBPN3/gnEAiz3kJ2uXy/BtepPcYbrJfCPbyVLvN2d1aPG mtV7sqpCAjMCOaUcboEaL+nCSfFqpg3c8nkDsniUAvREd+ZXjJyHRg4TGpzfim9BTU r+S/9Fw48YCg2fr8tjCvXkcZh1kgomI+le43jZgw= Date: Mon, 17 Oct 2022 17:46:28 -0700 To: mm-commits@vger.kernel.org, willy@infradead.org, vbabka@suse.cz, shuah@kernel.org, peterx@redhat.com, jhubbard@nvidia.com, jgg@nvidia.com, hughd@google.com, aarcange@redhat.com, david@redhat.com, akpm@linux-foundation.org From: Andrew Morton Subject: + mm-ksm-convert-break_ksm-to-use-walk_page_range_vma.patch added to mm-unstable branch Message-Id: <20221018004629.AF215C433D7@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org The patch titled Subject: mm/ksm: convert break_ksm() to use walk_page_range_vma() has been added to the -mm mm-unstable branch. Its filename is mm-ksm-convert-break_ksm-to-use-walk_page_range_vma.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-ksm-convert-break_ksm-to-use-walk_page_range_vma.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: David Hildenbrand Subject: mm/ksm: convert break_ksm() to use walk_page_range_vma() Date: Fri, 30 Sep 2022 16:19:30 +0200 FOLL_MIGRATION exists only for the purpose of break_ksm(), and actually, there is not even the need to wait for the migration to finish, we only want to know if we're dealing with a KSM page. Using follow_page() just to identify a KSM page overcomplicates GUP code. Let's use walk_page_range_vma() instead, because we don't actually care about the page itself, we only need to know a single property -- no need to even grab a reference on the page. In my setup (AMD Ryzen 9 3900X), running the KSM selftest to test unmerge performance on 2 GiB (taskset 0x8 ./ksm_tests -D -s 2048), this results in a performance degradation of ~4% (old: ~5010 MiB/s, new: ~4800 MiB/s). I don't think we particularly care for now. Link: https://lkml.kernel.org/r/20220930141931.174362-7-david@redhat.com Signed-off-by: David Hildenbrand Cc: Andrea Arcangeli Cc: Hugh Dickins Cc: Jason Gunthorpe Cc: John Hubbard Cc: Matthew Wilcox Cc: Peter Xu Cc: Shuah Khan Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- mm/ksm.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 62 insertions(+), 8 deletions(-) --- a/mm/ksm.c~mm-ksm-convert-break_ksm-to-use-walk_page_range_vma +++ a/mm/ksm.c @@ -39,6 +39,7 @@ #include #include #include +#include #include #include "internal.h" @@ -419,6 +420,60 @@ static inline bool ksm_test_exit(struct return atomic_read(&mm->mm_users) == 0; } +int break_ksm_pud_entry(pud_t *pud, unsigned long addr, unsigned long next, + struct mm_walk *walk) +{ + /* We only care about page tables to walk to a single base page. */ + if (pud_leaf(*pud) || !pud_present(*pud)) + return 1; + return 0; +} + +int break_ksm_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long next, + struct mm_walk *walk) +{ + bool *ksm_page = walk->private; + struct page *page = NULL; + pte_t *pte, ptent; + spinlock_t *ptl; + + /* We only care about page tables to walk to a single base page. */ + if (pmd_leaf(*pmd) || !pmd_present(*pmd)) + return 1; + + /* + * We only lookup a single page (a) no need to iterate; and (b) + * always return 1 to exit immediately and not iterate in the caller. + */ + pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl); + ptent = *pte; + + if (pte_none(ptent)) + return 1; + if (!pte_present(ptent)) { + swp_entry_t entry = pte_to_swp_entry(ptent); + + /* + * We only care about migration of KSM pages. As KSM pages + * remain KSM pages until freed, no need to wait here for + * migration to end to identify such. + */ + if (is_migration_entry(entry)) + page = pfn_swap_entry_to_page(entry); + } else { + page = vm_normal_page(walk->vma, addr, ptent); + } + if (page && PageKsm(page)) + *ksm_page = true; + pte_unmap_unlock(pte, ptl); + return 1; +} + +static const struct mm_walk_ops break_ksm_ops = { + .pud_entry = break_ksm_pud_entry, + .pmd_entry = break_ksm_pmd_entry, +}; + /* * We use break_ksm to break COW on a ksm page by triggering unsharing, * such that the ksm page will get replaced by an exclusive anonymous page. @@ -434,20 +489,19 @@ static inline bool ksm_test_exit(struct */ static int break_ksm(struct vm_area_struct *vma, unsigned long addr) { - struct page *page; vm_fault_t ret = 0; + if (WARN_ON_ONCE(!IS_ALIGNED(addr, PAGE_SIZE))) + return -EINVAL; + do { bool ksm_page = false; cond_resched(); - page = follow_page(vma, addr, - FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE); - if (IS_ERR_OR_NULL(page)) - break; - if (PageKsm(page)) - ksm_page = true; - put_page(page); + ret = walk_page_range_vma(vma, addr, addr + PAGE_SIZE, + &break_ksm_ops, &ksm_page); + if (WARN_ON_ONCE(ret < 0)) + return ret; if (!ksm_page) return 0; _ Patches currently in -mm which might be from david@redhat.com are selftests-vm-add-test-to-measure-madv_unmergeable-performance.patch mm-ksm-simplify-break_ksm-to-not-rely-on-vm_fault_write.patch mm-remove-vm_fault_write.patch mm-ksm-fix-ksm-cow-breaking-with-userfaultfd-wp-via-fault_flag_unshare.patch mm-pagewalk-add-walk_page_range_vma.patch mm-ksm-convert-break_ksm-to-use-walk_page_range_vma.patch mm-gup-remove-foll_migration.patch