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=-8.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,USER_AGENT_GIT autolearn=ham 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 4A893C43218 for ; Thu, 25 Apr 2019 13:33:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0B78D206BF for ; Thu, 25 Apr 2019 13:33:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=zoho.com header.i=yehs2007@zoho.com header.b="bXrYeNvL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729328AbfDYNdG (ORCPT ); Thu, 25 Apr 2019 09:33:06 -0400 Received: from sender4-pp-o95.zoho.com ([136.143.188.95]:25562 "EHLO sender4-pp-o95.zoho.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726514AbfDYNdG (ORCPT ); Thu, 25 Apr 2019 09:33:06 -0400 ARC-Seal: i=1; a=rsa-sha256; t=1556199135; cv=none; d=zoho.com; s=zohoarc; b=eWqfyXO8bSYbwmTzglfVYw+G/bc6uVPSXgV5zpMbyd7/pGbZhY2C4p6Zx/3xQ07gSQTbQ7QBjDoQztUEN43XbvCoav5utwf4Y6hSejHXI8QxATegVAkffENNvDa+nxC9R8/39YdeutrHh9rcvJ7uLLtQ+tAtMjwhMHecPJgVCGA= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zoho.com; s=zohoarc; t=1556199135; h=Cc:Date:From:In-Reply-To:Message-ID:References:Subject:To:ARC-Authentication-Results; bh=FIxzx8ufezxHUGnlKslImct4gA4BATVr8SFi532iUlo=; b=d9OV3+NJDXlItys5pHhkC/VLL+o7bwgYHmjNITIsiZ9lHIbK8jUot8r9KHTo2t+mUz6UHA1rPC0ytXTUrBkjSH/kQaND7wu1+0KCgbtEjJFg2xGAxQGcH7rZEJg2JeSe9HxyM3AqTr5959b4zOaUNu0+bm/rk3TCgE/+QnvLG18= ARC-Authentication-Results: i=1; mx.zoho.com; dkim=pass header.i=zoho.com; spf=pass smtp.mailfrom=yehs2007@zoho.com; dmarc=pass header.from= header.from= DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=zapps768; d=zoho.com; h=from:to:cc:subject:date:message-id:in-reply-to:references; b=Uu/tQ2GZuXQyCOgwBxFlEy0JwTFbrHsYg9eEvdWDl/0UBeMWleQYQdFsjYNkvxGcnpof3gGumjLR oN/jgJT81Dm5XaClA0ViAt0M9a4mqFgo8qhmW/y8R6zvfec7vsko DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1556199135; s=default; d=zoho.com; i=yehs2007@zoho.com; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References; l=3402; bh=FIxzx8ufezxHUGnlKslImct4gA4BATVr8SFi532iUlo=; b=bXrYeNvL0TOjnFTMiTnmT+bnNUFNf0hxn8sWUNIyn4/PSq+9HhDK3yaaWAu791FW psGIvA6dgbJEMiJeindrjvzrtg8FSwj3Fnv+d4v6fgOSF/dcUTJW4ng55+ASEnPFrpd mkiZBmdnm/G2roZhkUVTiXsb7FjRgIMsRNtP6W5k= Received: from YEHS1XR3054QMS.lenovo.com (123.120.108.196 [123.120.108.196]) by mx.zohomail.com with SMTPS id 1556199133111253.18143767731408; Thu, 25 Apr 2019 06:32:13 -0700 (PDT) From: Huaisheng Ye To: mpatocka@redhat.com, snitzer@redhat.com, agk@redhat.com Cc: prarit@redhat.com, chengnt@lenovo.com, dm-devel@redhat.com, linux-kernel@vger.kernel.org, Huaisheng Ye Subject: [PATCH v2 4/4] dm writecache: avoid unnecessary lookups in writecache_find_entry Date: Thu, 25 Apr 2019 21:31:20 +0800 Message-Id: <20190425133120.13088-5-yehs2007@zoho.com> X-Mailer: git-send-email 2.17.0.windows.1 In-Reply-To: <20190425133120.13088-1-yehs2007@zoho.com> References: <20190425133120.13088-1-yehs2007@zoho.com> X-ZohoMailClient: External Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Huaisheng Ye Only when entry has been found, that would only be necessary to check the lowest or highest seq-count. Add local variable "found" in writecache_find_entry, if no entry has been found, it is meaningless that having a useless rb_prev or rb_next. This patch is not designed for fixing logical error. That is used for optimizing the behavior of writecache_find_entry. Give an example to illustrate the point below. Suppose that is the case, here is a normal READ bio comes to writecache_map. And because of bio's direction is READ, writecache_find_entry would be called with flags WFE_RETURN_FOLLOWING. Now there are two scenarios, 1. writecache_find_entry successfully get an existing entry by searching rb_tree, we could call it HIT. Then the first 'while' will be finished by 'break'. Next it will move to second 'while' loop, because of the flags hasn't been marked as WFE_LOWEST_SEQ. writecache_find_entry will try to return an entry with HIGHEST_SEQ, if there are other entries which has same original_sector in rb_tree. For this situation, the current code is okay to deal with that. 2. writecache_find_entry couldn't get an existing entry from rb_tree, we could call it MISS. Because of same flags WFE_RETURN_FOLLOWING, writecache_find_entry will get other entry, which's original_sector will slightly larger than input parameter block, with big probability. For this scenario, function writecache_find_entry doesn't need to enter second 'while' loop. But current code would still try to check there were other entry with same original_sector. So the additional rb_next or rb_prev is unnecessary by this case, also the code doesn't need to compare the original_sector of 'e2' with parameter 'block'. This patch is designed to optimize the second case. so it could skip the second 'while' loop when the block is missed from rb_tree. Signed-off-by: Huaisheng Ye --- drivers/md/dm-writecache.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c index ddf1732..047ae09 100644 --- a/drivers/md/dm-writecache.c +++ b/drivers/md/dm-writecache.c @@ -537,14 +537,18 @@ static struct wc_entry *writecache_find_entry(struct dm_writecache *wc, { struct wc_entry *e; struct rb_node *node = wc->tree.rb_node; + bool found = false; if (unlikely(!node)) return NULL; while (1) { e = container_of(node, struct wc_entry, rb_node); - if (read_original_sector(wc, e) == block) + if (read_original_sector(wc, e) == block) { + found = true; break; + } + node = (read_original_sector(wc, e) >= block ? e->rb_node.rb_left : e->rb_node.rb_right); if (unlikely(!node)) { @@ -564,7 +568,8 @@ static struct wc_entry *writecache_find_entry(struct dm_writecache *wc, } } - while (1) { + /* only need to check lowest or highest seq-count when entry has been found */ + while (found) { struct wc_entry *e2; if (flags & WFE_LOWEST_SEQ) node = rb_prev(&e->rb_node); @@ -577,6 +582,9 @@ static struct wc_entry *writecache_find_entry(struct dm_writecache *wc, return e; e = e2; } + + /* no entry has been found, return the following entry */ + return e; } static void writecache_insert_entry(struct dm_writecache *wc, struct wc_entry *ins) -- 1.8.3.1