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=-8.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 3DF25C282DD for ; Fri, 10 Jan 2020 16:46:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 15EE820721 for ; Fri, 10 Jan 2020 16:46:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578674762; bh=qVX1na3eKlg+jVvB2Llvljn85uT53mBXa1in+HWm/0Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=tr4Iejn7CYG2BRz+fi9TVMKSPBGUHXxBDiXURc69qtdLNjp3y3Ntw6iigwuGoKe2P SMW/gR831xpM4raQhfN5HdyPlWW4LJ88oVfU+4EyhZkXNM5lK6/F1TOX/FTtSkGYR7 tqVnjlcYIYeuBCnbZMWTvdFQvdIG641JXPRxGQ94= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728871AbgAJQqB (ORCPT ); Fri, 10 Jan 2020 11:46:01 -0500 Received: from mail-pf1-f193.google.com ([209.85.210.193]:38102 "EHLO mail-pf1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728107AbgAJQqB (ORCPT ); Fri, 10 Jan 2020 11:46:01 -0500 Received: by mail-pf1-f193.google.com with SMTP id x185so1401051pfc.5; Fri, 10 Jan 2020 08:46:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=+zuEtxuDCNNPIe3EcK+m31UcAVGsvqFLpzNCTX1NQ6U=; b=dIt3wHfnfA4X8SdRxF8O7+f85bw6pcjAzv4vaXLPdUtjl1QvutERX5OwINkIfsfXK8 QPCKaL5qS5PzCkxDpE4qG4ExpUJwtjVaCvdxKptkrE1nKCmKebThJPUnBtk7GEvccAcA RNYZyowteQU6mQRm5t+IHI7RzgstnhE2wtibH32It418Glfv07T+JJDLnfoKR9jTyk6T PXyLsiXRHMFfZv8cd3P4c8aAB0uj4/JK03YvpCWX5f2OeIBRYn0BtUTsjSwz6qrhXAdP Eq67EYzE0ZePFn2zYF+19xz6vQdKDq/vT//adK+u6vNKQu/BGePN+xNHmNDDD6x8v+Ho ReNA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=+zuEtxuDCNNPIe3EcK+m31UcAVGsvqFLpzNCTX1NQ6U=; b=EtrKDAPOjJu4VcUJ2RUnE9EuY8a7/HAmbbnwLxCdwdw1WDJ5FPgDZRQUEQELJtkETu 4XJ+HfFvoJl6/4c9i0wzpk6om4VGGHlNuNyjygLMM8m54njP4HyoNkkOIfG29fr4JXF6 mSmxXq/OPVfYOyeCc6oh1vD2AOiFqpe3U+2W8uolZQAJ9/GfibUOen6xungRsLu+infN pVSsjPwC+tyCskp56xANADjAoBj6hDRbxn2iEXtjCD+mu4j6La9mMrJ4MgaCVxkpBbW9 eOUnzl3E214yAEuewhnMAP0VbgOPsP+JDU9p2lZZH/9etzrxNbrnbysHlCk8sFZ/LQIH kWqw== X-Gm-Message-State: APjAAAWROPdYMSfWVK2XYHPqF+Gw1H02uJn8LCBEShpX4Pf4Yc6wKat+ 4HKB8sqL780vvSu+SAF/umHTH7Jg X-Google-Smtp-Source: APXvYqx+sIxZF1KBeRyr4xjIy8PaGrt26bkAoyteGY5HatV0Fw+HzIXpZGWuYnFCU74+3OyOaReXzA== X-Received: by 2002:aa7:961b:: with SMTP id q27mr5143360pfg.23.1578674760023; Fri, 10 Jan 2020 08:46:00 -0800 (PST) Received: from google.com ([2620:15c:211:1:3e01:2939:5992:52da]) by smtp.gmail.com with ESMTPSA id o17sm3389435pjq.1.2020.01.10.08.45.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Jan 2020 08:45:58 -0800 (PST) Date: Fri, 10 Jan 2020 08:45:57 -0800 From: Minchan Kim To: Taejoon Song , Andrew Morton Cc: ngupta@vflare.org, sergey.senozhatsky.work@gmail.com, axboe@kernel.dk, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, yjay.kim@lge.com Subject: Re: [PATCH] zram: try to avoid worst-case scenario on same element pages Message-ID: <20200110164557.GA152286@google.com> References: <1578642001-11765-1-git-send-email-taejoon.song@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1578642001-11765-1-git-send-email-taejoon.song@lge.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Andrew, Previous version has a off-by-one error to check every unsigned long bytes so it misses a unsigned long bytes in PAGE_SIZE. It could make zram believe it's same page but not true. This is a new patch Tejun fixed so could you replace [1] with this version? Thanks. [1] mmotm: zram-try-to-avoid-worst-case-scenario-on-same-element-pages.patch with On Fri, Jan 10, 2020 at 04:40:01PM +0900, Taejoon Song wrote: > The worst-case scenario on finding same element pages is that almost > all elements are same at the first glance but only last few elements > are different. > > Since the same element tends to be grouped from the beginning of the > pages, if we check the first element with the last element before > looping through all elements, we might have some chances to quickly > detect non-same element pages. > > 1. Test is done under LG webOS TV (64-bit arch) > 2. Dump the swap-out pages (~819200 pages) > 3. Analyze the pages with simple test script which counts the iteration > number and measures the speed at off-line > > Under 64-bit arch, the worst iteration count is PAGE_SIZE / 8 bytes = 512. > The speed is based on the time to consume page_same_filled() function only. > The result, on average, is listed as below: > > Num of Iter Speed(MB/s) > Looping-Forward (Orig) 38 99265 > Looping-Backward 36 102725 > Last-element-check (This Patch) 33 125072 > > The result shows that the average iteration count decreases by 13% and > the speed increases by 25% with this patch. This patch does not increase > the overall time complexity, though. > > I also ran simpler version which uses backward loop. Just looping backward > also makes some improvement, but less than this patch. > > Signed-off-by: Taejoon Song Acked-by: Minchan Kim > --- > drivers/block/zram/zram_drv.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > index 4285e75..71d5946 100644 > --- a/drivers/block/zram/zram_drv.c > +++ b/drivers/block/zram/zram_drv.c > @@ -207,14 +207,17 @@ static inline void zram_fill_page(void *ptr, unsigned long len, > > static bool page_same_filled(void *ptr, unsigned long *element) > { > - unsigned int pos; > unsigned long *page; > unsigned long val; > + unsigned int pos, last_pos = PAGE_SIZE / sizeof(*page) - 1; > > page = (unsigned long *)ptr; > val = page[0]; > > - for (pos = 1; pos < PAGE_SIZE / sizeof(*page); pos++) { > + if (val != page[last_pos]) > + return false; > + > + for (pos = 1; pos < last_pos; pos++) { FYI, this is fixed part from previous one. > if (val != page[pos]) > return false; > } > -- > 2.7.4 >