From patchwork Fri Sep 30 14:19:30 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 12995506 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 AC507C4332F for ; Fri, 30 Sep 2022 14:21:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232027AbiI3OVW (ORCPT ); Fri, 30 Sep 2022 10:21:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45000 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231968AbiI3OUu (ORCPT ); Fri, 30 Sep 2022 10:20:50 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3E435B6573 for ; Fri, 30 Sep 2022 07:20:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1664547648; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=QdWmhT+XCWVUBSGE3ZoFfg/O04jXqhSLTEOmUwlj3I8=; b=IngFk+YsCeKTCqqCzWzv2lwksAZAkLGwdOu4g2ZT7Ggu0XbNeH4C/ntmWwYmiQImhvZkUB isbZgdE41GQ10JO1XLvJwTFV7vmPwktlso2DCkMk/gN7iJTWUmsNdKRvPcXYMz+puJv6Zy 4CLItYDKQwGnLUH1M49VLXL3t7RaOi8= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-499-ZiHXnUcHNF6VF1dflaLRxQ-1; Fri, 30 Sep 2022 10:20:47 -0400 X-MC-Unique: ZiHXnUcHNF6VF1dflaLRxQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 8F6342A5955A; Fri, 30 Sep 2022 14:20:46 +0000 (UTC) Received: from t480s.redhat.com (unknown [10.39.194.187]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0CB731121314; Fri, 30 Sep 2022 14:20:32 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-kselftest@vger.kernel.org, David Hildenbrand , Andrew Morton , Shuah Khan , Hugh Dickins , Vlastimil Babka , Peter Xu , Andrea Arcangeli , "Matthew Wilcox (Oracle)" , Jason Gunthorpe , John Hubbard Subject: [PATCH v1 6/7] mm/ksm: convert break_ksm() to use walk_page_range_vma() Date: Fri, 30 Sep 2022 16:19:30 +0200 Message-Id: <20220930141931.174362-7-david@redhat.com> In-Reply-To: <20220930141931.174362-1-david@redhat.com> References: <20220930141931.174362-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org 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. Signed-off-by: David Hildenbrand Signed-off-by: David Hildenbrand --- mm/ksm.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 62 insertions(+), 8 deletions(-) diff --git a/mm/ksm.c b/mm/ksm.c index 4d7bcf7da7c3..814c1a37c323 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -39,6 +39,7 @@ #include #include #include +#include #include #include "internal.h" @@ -452,6 +453,60 @@ static inline bool ksm_test_exit(struct mm_struct *mm) 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. @@ -467,20 +522,19 @@ static inline bool ksm_test_exit(struct mm_struct *mm) */ 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;