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 77226C433ED for ; Thu, 1 Apr 2021 19:23:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 56EF36101E for ; Thu, 1 Apr 2021 19:23:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234647AbhDATW6 (ORCPT ); Thu, 1 Apr 2021 15:22:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51310 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234488AbhDATWo (ORCPT ); Thu, 1 Apr 2021 15:22:44 -0400 Received: from mail-qk1-x74a.google.com (mail-qk1-x74a.google.com [IPv6:2607:f8b0:4864:20::74a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 23057C049FC8 for ; Thu, 1 Apr 2021 11:21:33 -0700 (PDT) Received: by mail-qk1-x74a.google.com with SMTP id k68so4310753qke.2 for ; Thu, 01 Apr 2021 11:21:33 -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=7FFTxJfhBub0ermj70tsntXQaF5NxHdv1LLLlAgh3Tg=; b=IvjDKg2QrBzk4nuwOJe7alSzTfjXQP4b7KooEke+eiaaPZYUwJz1yuqQH5tTDFEK98 7Lk7/uotQuA8WyQRHVZilIOzw6ATk5kIoJ1FMiDxVUWxXOo3lA5bkZ4nsXxDQzVFsb6I wQhRBt2hS9Y68Z/VRvYd4JI0ecn1ecAgTx2aT51YYHfrUeGCT4o3Vdi3jgTB0NTGksYH Ag5biBiLOCYWQEf42Fjbyn8pmn5S1XUm0OEFDO56SyluU3/SAdNQKqcz6FZKg12/s5jO hzYsgH8HQUmWqtuOIg96pFQdNKziF+3zTtd959cnOlMDo9R7W+V7/eGk9S+ly3+hVUP8 m61A== 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=7FFTxJfhBub0ermj70tsntXQaF5NxHdv1LLLlAgh3Tg=; b=WTXlO6BgN5/NvtQwHK1hb2WAm/JNdlbeWdhcDWh2Yrpo/At15m+O4um//QE2lcKFFq Mx3+uCK397IibmQ8wSI066YTJ1ESoV0ihjlLrlbUfUInqiPkqybWd1+D0/JDHzNPvtRo iACRSRBfF5+UVLQaScWL5vJ/1cw5SFDJ8SYBwxs7JBkZEcCLytI1xwt7kzf8COXn8uTz GwYWaPGWDmyDwIQ0etG0uegIDN2ifGK2OS3pfPYCq044xUTwOUxCaW86itx7zZLco1iV HNjRh4ZMhyPc71W6jZnXJIowbJO2S+gZ4Ih1xQVKX7pr2IDzP4Qg+JyfTN/2erQhrGO4 cfMg== X-Gm-Message-State: AOAM5321RdeNh9LLR3lbQKfBnPlhRpQ7koI2hCOK5/Wdcj/MeJFnAD9X 4hQnmYwNleoPjEVAH8cn5aiEGpCz0kY= X-Google-Smtp-Source: ABdhPJxh3T2CByrPxU0x0VwYvdWMkwXm0bV1SkaFoboTivfYvAc2IT1vS+/1Q743N1AN5Z/g9DCa/yCPEVI= X-Received: from surenb1.mtv.corp.google.com ([2620:15c:211:200:899:1066:21fc:b3c5]) (user=surenb job=sendgmr) by 2002:a0c:fecd:: with SMTP id z13mr9375738qvs.43.1617301292340; Thu, 01 Apr 2021 11:21:32 -0700 (PDT) Date: Thu, 1 Apr 2021 11:21:22 -0700 In-Reply-To: <20210401182125.171484-1-surenb@google.com> Message-Id: <20210401182125.171484-3-surenb@google.com> Mime-Version: 1.0 References: <20210401182125.171484-1-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, surenb@google.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 3874acce1472..d95a4573a273 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2847,49 +2847,25 @@ static vm_fault_t 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