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=-5.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 72836C4741F for ; Thu, 1 Oct 2020 12:30:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2CFEC21481 for ; Thu, 1 Oct 2020 12:30:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="GnrnpGVO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732360AbgJAMah (ORCPT ); Thu, 1 Oct 2020 08:30:37 -0400 Received: from mx2.suse.de ([195.135.220.15]:34150 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731987AbgJAMaf (ORCPT ); Thu, 1 Oct 2020 08:30:35 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1601555434; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=uCm4uXOnrpWMmMZOVA7wh6ICDudob2h+p29v5JSL4lU=; b=GnrnpGVOycrS6i3U5eUDgMPqc4ZSmxHImP6IM3Q9oRdFfgGHwzWCI5H+2lZar3wd+EJgGv QEiFqFCDYgSp1OTN9AbCtO5mEALDiuKWhR/Pqkq7y6hzSbhehovg/ZXqPG6QVOD7X2crvB fZtYaxIuElKuddlIJBEQ3JPWMaSRAqU= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 9D2BAAFD7; Thu, 1 Oct 2020 12:30:34 +0000 (UTC) Date: Thu, 1 Oct 2020 14:30:32 +0200 From: Michal Hocko To: Sebastiaan Meijer Cc: akpm@linux-foundation.org, buddy.lumpkin@oracle.com, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mgorman@suse.de, riel@surriel.com, willy@infradead.org Subject: Re: [RFC PATCH 1/1] vmscan: Support multiple kswapd threads per node Message-ID: <20201001123032.GC22560@dhcp22.suse.cz> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 30-09-20 21:27:12, Sebastiaan Meijer wrote: > > yes it shows the bottleneck but it is quite artificial. Read data is > > usually processed and/or written back and that changes the picture a > > lot. > Apologies for reviving an ancient thread (and apologies in advance for my lack > of knowledge on how mailing lists work), but I'd like to offer up another > reason why merging this might be a good idea. > > From what I understand, zswap runs its compression on the same kswapd thread, > limiting it to a single thread for compression. Given enough processing power, > zswap can get great throughput using heavier compression algorithms like zstd, > but this is currently greatly limited by the lack of threading. Isn't this a problem of the zswap implementation rather than general kswapd reclaim? Why zswap doesn't do the same as normal swap out in a context outside of the reclaim? My recollection of the particular patch is dimm but I do remember it tried to add more kswapd threads which would just paper over the problem you are seein rather than solve it. -- Michal Hocko SUSE Labs