From patchwork Thu Apr 1 18:17:38 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Suren Baghdasaryan X-Patchwork-Id: 414277 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 27D5BC433B4 for ; Thu, 1 Apr 2021 19:21:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F0B8B6108B for ; Thu, 1 Apr 2021 19:21:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234872AbhDATVT (ORCPT ); Thu, 1 Apr 2021 15:21:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51146 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234376AbhDATVL (ORCPT ); Thu, 1 Apr 2021 15:21:11 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6FE3CC048F2D for ; Thu, 1 Apr 2021 11:17:52 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id w7so6623489ybq.4 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=VVc04NJ/q/qr55DR3orxw+Xu/0Bfu6/TjQwAfHvq9ai/XQN3349l09FeLd6e5xR1Up z7MtoTqmnyeYRSfSLrJhQXAsBFyMhPFLwdP35HKtiDkmQhutF187sg5r7wBMZs1Ehx0m fWvUBbOQyHC9nQdFKbsQ8MLYM/7DTzdvuIOw1bm3BGtq6fXnBMoksaHdH6nSOnhL5jVf UhqO3AEK6ISyJ9UukA1GOH+zSrLjfaDtpKQyTPoQpB0BbHGF10DAdJQIiM5G+e+kKzQB 2GK1YAtMhzzoE3uKm9CIXKStcyqAf03ERwDYdrkRB7rbq5s1HCaAgsrRZku8hs9bv6lU /ndQ== X-Gm-Message-State: AOAM530duRznJ5RFga48ATruLSTpXqFXDGiLTXY+OPFSR9WvMBU1ZliJ 6L2DAoZ96SUt1RFlZjaEZIqVKNwW4Q5eYOvHTH9oTZnfnRi1Fh24Z36ALxpyCpiSp4BZ/jZhuSs Oeq8Q8MyXIPiA4Cy77IRbGFQJSlZw9Lzz5EH2rROnsQY6m9qCkUm1q/B92CsvjA== 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 Precedence: bulk List-ID: X-Mailing-List: stable@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);