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 X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1BB48C433ED for ; Thu, 1 Apr 2021 19:21:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E756D61001 for ; Thu, 1 Apr 2021 19:21:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234768AbhDATV3 (ORCPT ); Thu, 1 Apr 2021 15:21:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51092 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234633AbhDATVJ (ORCPT ); Thu, 1 Apr 2021 15:21:09 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 659F7C048F2C for ; Thu, 1 Apr 2021 11:17:52 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id v6so6571369ybk.9 for ; Thu, 01 Apr 2021 11:17:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=SQmWyihLynq1vxlXIZnnYrhWJiVcwsY6ykKbBmHmp/w=; b=P0s9nmSUOso3M4IwpWpTuWzReIWrwsNczHXACiQLGjUVD59T6zAZhOZTKqVDoOGZPM ELqsOa6/b6oxSB/BpxzS6H8PFYB2iNb3A6Ko5THKzv1XQSjGF0+OV+bAA2hzf1oei2G9 waMHYgD1BtXe2ARHAGth7KBqipiyJj+jHcsvAVXmhu4iSPF6R/LnnUdRRxE1RXCxCoZF DYnGQpp1mo3XFHEyCzTOcvoC2c1sCFBkMLDkU/KUfVUDnbg/WpsvqF33X3hoeqqLqxF9 6nmCH+s3SYWbdx87hp8/JLThMxWLAoLpf29erRSjdcs/BTJ4EPhMOa4y7k/+x2mi9m4I YwXQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=SQmWyihLynq1vxlXIZnnYrhWJiVcwsY6ykKbBmHmp/w=; b=JNsWAVaYaGU4Lvu6NrNd03anRsGEARoOP92q3l4EhnvPcVtIf/Bgdy8smXtZDk44kv oCIFWeXJeRwA0tvdvXtmGV4eED4zEkJ/EJcpGvymRgSBkWflQAz+YaSPvRZ1xboULlSP pRWlEY8XsUB8Y9uTbDjrETSoem2ZWYD0OeJbfLcghlXNtim2IZ47SlJlHrTKspl4tFb0 KU+RPcLMk3ObxhC503YOkmK43ol/i17d9VFjfOCymREwiJDLzDqPYj7mGxRVA/O+Z0Tz 7QoglRbMeRjFG5eNTLmyd8zwAybh2qGJJYfTJYUHsvswveiP9m7UYN7XtdJEgWUoDjei I6Cw== X-Gm-Message-State: AOAM532ib9ZhrK4N0Nsad05Xt+1+5kvNIgFP4QYp/oL7qQdVVKaDq766 McXhD3DaQzNibCrM8x6NnseneW2PzTs= X-Google-Smtp-Source: ABdhPJw36/jc6xurXz6R7Fq8v13fytweZrUVCqZMZTqkwel5NP1HU4iFmgcBmdujTpkEUebtBKXFFUZhRpM= X-Received: from surenb1.mtv.corp.google.com ([2620:15c:211:200:899:1066:21fc:b3c5]) (user=surenb job=sendgmr) by 2002:a25:6f44:: with SMTP id k65mr12694020ybc.218.1617301071663; Thu, 01 Apr 2021 11:17:51 -0700 (PDT) Date: Thu, 1 Apr 2021 11:17:38 -0700 In-Reply-To: <20210401181741.168763-1-surenb@google.com> Message-Id: <20210401181741.168763-3-surenb@google.com> Mime-Version: 1.0 References: <20210401181741.168763-1-surenb@google.com> X-Mailer: git-send-email 2.31.0.291.g576ba9dcdaf-goog Subject: [PATCH 2/5] mm: do_wp_page() simplification From: Suren Baghdasaryan To: stable@vger.kernel.org Cc: gregkh@linuxfoundation.org, jannh@google.com, ktkhai@virtuozzo.com, torvalds@linux-foundation.org, shli@fb.com, namit@vmware.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com, Peter Xu Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Linus Torvalds How about we just make sure we're the only possible valid user fo the page before we bother to reuse it? Simplify, simplify, simplify. And get rid of the nasty serialization on the page lock at the same time. [peterx: add subject prefix] Signed-off-by: Linus Torvalds Signed-off-by: Peter Xu Signed-off-by: Linus Torvalds --- mm/memory.c | 58 ++++++++++++++++------------------------------------- 1 file changed, 17 insertions(+), 41 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 6920bfb3f89c..e84648d81d6d 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2832,49 +2832,25 @@ static int do_wp_page(struct vm_fault *vmf) * not dirty accountable. */ if (PageAnon(vmf->page)) { - int total_map_swapcount; - if (PageKsm(vmf->page) && (PageSwapCache(vmf->page) || - page_count(vmf->page) != 1)) + struct page *page = vmf->page; + + /* PageKsm() doesn't necessarily raise the page refcount */ + if (PageKsm(page) || page_count(page) != 1) + goto copy; + if (!trylock_page(page)) + goto copy; + if (PageKsm(page) || page_mapcount(page) != 1 || page_count(page) != 1) { + unlock_page(page); goto copy; - if (!trylock_page(vmf->page)) { - get_page(vmf->page); - pte_unmap_unlock(vmf->pte, vmf->ptl); - lock_page(vmf->page); - vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, - vmf->address, &vmf->ptl); - if (!pte_same(*vmf->pte, vmf->orig_pte)) { - unlock_page(vmf->page); - pte_unmap_unlock(vmf->pte, vmf->ptl); - put_page(vmf->page); - return 0; - } - put_page(vmf->page); - } - if (PageKsm(vmf->page)) { - bool reused = reuse_ksm_page(vmf->page, vmf->vma, - vmf->address); - unlock_page(vmf->page); - if (!reused) - goto copy; - wp_page_reuse(vmf); - return VM_FAULT_WRITE; - } - if (reuse_swap_page(vmf->page, &total_map_swapcount)) { - if (total_map_swapcount == 1) { - /* - * The page is all ours. Move it to - * our anon_vma so the rmap code will - * not search our parent or siblings. - * Protected against the rmap code by - * the page lock. - */ - page_move_anon_rmap(vmf->page, vma); - } - unlock_page(vmf->page); - wp_page_reuse(vmf); - return VM_FAULT_WRITE; } - unlock_page(vmf->page); + /* + * Ok, we've got the only map reference, and the only + * page count reference, and the page is locked, + * it's dark out, and we're wearing sunglasses. Hit it. + */ + wp_page_reuse(vmf); + unlock_page(page); + return VM_FAULT_WRITE; } else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) == (VM_WRITE|VM_SHARED))) { return wp_page_shared(vmf); -- 2.31.0.291.g576ba9dcdaf-goog