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, 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 8DD20C433DB for ; Wed, 31 Mar 2021 09:26:33 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CA0A7619C1 for ; Wed, 31 Mar 2021 09:26:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CA0A7619C1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 1BA2D6B0081; Wed, 31 Mar 2021 05:26:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 143BD6B0082; Wed, 31 Mar 2021 05:26:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id F26EB6B0083; Wed, 31 Mar 2021 05:26:31 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0078.hostedemail.com [216.40.44.78]) by kanga.kvack.org (Postfix) with ESMTP id D3EE16B0081 for ; Wed, 31 Mar 2021 05:26:31 -0400 (EDT) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 882001EE6 for ; Wed, 31 Mar 2021 09:26:31 +0000 (UTC) X-FDA: 77979638982.15.251C5E7 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf09.hostedemail.com (Postfix) with ESMTP id B680D600010B for ; Wed, 31 Mar 2021 09:26:30 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id A6F39AEAE; Wed, 31 Mar 2021 09:26:29 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 6B66A1E4415; Wed, 31 Mar 2021 11:26:29 +0200 (CEST) Date: Wed, 31 Mar 2021 11:26:29 +0200 From: Jan Kara To: Matthew Wilcox Cc: Jan Kara , linux-mm@kvack.org, Johannes Weiner Subject: Re: [PATCH 2/3] flex_proportions: Allow N events instead of 1 Message-ID: <20210331092629.GD30749@quack2.suse.cz> References: <20210322201116.2149432-1-willy@infradead.org> <20210322201116.2149432-3-willy@infradead.org> <20210322223527.GX1719932@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210322223527.GX1719932@casper.infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: B680D600010B X-Stat-Signature: 61we19573madfhh91r1xekenobgo3kyo Received-SPF: none (suse.cz>: No applicable sender policy available) receiver=imf09; identity=mailfrom; envelope-from=""; helo=mx2.suse.de; client-ip=195.135.220.15 X-HE-DKIM-Result: none/none X-HE-Tag: 1617182790-450836 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon 22-03-21 22:35:27, Matthew Wilcox wrote: > On Mon, Mar 22, 2021 at 08:11:15PM +0000, Matthew Wilcox (Oracle) wrote: > > -void __fprop_inc_percpu_max(struct fprop_global *p, > > - struct fprop_local_percpu *pl, int max_frac) > > +void __fprop_add_percpu_max(struct fprop_global *p, > > + struct fprop_local_percpu *pl, int max_frac, long nr) > > { > > if (unlikely(max_frac < FPROP_FRAC_BASE)) { > > Oh, I meant to ask ... should this change? Should it be: > > if (unlikely(max_frac < FPROP_FRAC_BASE / nr)) > (or something similar that copes with overflow properly) > I must confess to not understanding exactly how flex_proportions works. No, __fprop_inc_percpu_max() implements "saturation" arithmetics on fractions. So if the fraction tracked by 'pl' exceeds max_frac/FPROP_FRAC_BASE, we don't want to increment 'pl' further. If 'nr' is going to be small, we probably don't care that we somewhat exceed the max_frac/FPROP_FRAC_BASE. But I suppose 'nr' can be say 512 at which point (given FPROP_FRAC_BASE is 1024) one addition can make a very significant difference. So we probably need to be more clever like: if (unlikely(max_frac < FPROP_FRAC_BASE)) { unsigned long numerator, denominator; s64 tmp; fprop_fraction_percpu(p, pl, &numerator, &denominator); /* Adding 'nr' to fraction exceeds max_frac/FPROP_FRAC_BASE? */ tmp = (u64)denominator * max_frac - ((u64)numerator << FPROP_FRAC_SHIFT); if (tmp < 0) { /* Maximum fraction already exceeded? */ return; } else if (tmp < nr * (FPROP_FRAC_BASE - max_frac)) { /* Add just enough for the fraction to saturate */ nr = div_u64(tmp + FPROP_FRAC_BASE - max_frac - 1, FPROP_FRAC_BASE - max_frac); } } Honza -- Jan Kara SUSE Labs, CR