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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id C9DD3C38145 for ; Thu, 8 Sep 2022 15:39:04 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4FE656B0072; Thu, 8 Sep 2022 11:39:04 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4AEDA6B0073; Thu, 8 Sep 2022 11:39:04 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 375D68D0003; Thu, 8 Sep 2022 11:39:04 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 281126B0072 for ; Thu, 8 Sep 2022 11:39:04 -0400 (EDT) Received: from smtpin22.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 02BA3160338 for ; Thu, 8 Sep 2022 15:39:03 +0000 (UTC) X-FDA: 79889326608.22.D7A7DF5 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by imf15.hostedemail.com (Postfix) with ESMTP id 7D3B0A0070 for ; Thu, 8 Sep 2022 15:39:03 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 2F783B8214D; Thu, 8 Sep 2022 15:39:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3B900C433D7; Thu, 8 Sep 2022 15:39:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1662651540; bh=zZ/SyZ5uIrt8M1sN+XQtWuDHRLfUcWLVoooJIAPUxWc=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=VNj8EE9Tsz+k+9CeVk3OH0tXqA2Bek+2sVutF1nf5+f3H6uQsmbmuIpt2w3+Oa4gN 5tIzImAjWGJsCo7KdraKE/T3mvvwGbieq+imtYEDiG1WLvGDyvP2iO1H7VCFBa6jNm cCz9UIj4TRuhegDcTp3YHsRqbQobf2QswLBu+AZk= Date: Thu, 8 Sep 2022 08:38:59 -0700 From: Andrew Morton To: "Sun, Jiebin" Cc: Tim Chen , vasily.averin@linux.dev, shakeelb@google.com, dennis@kernel.org, tj@kernel.org, cl@linux.com, ebiederm@xmission.com, legion@kernel.org, manfred@colorfullife.com, alexander.mikhalitsyn@virtuozzo.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, tim.c.chen@intel.com, feng.tang@intel.com, ying.huang@intel.com, tianyou.li@intel.com, wangyang.guo@intel.com Subject: Re: [PATCH v4] ipc/msg: mitigate the lock contention with percpu counter Message-Id: <20220908083859.24c989f08d62ddbd031005de@linux-foundation.org> In-Reply-To: References: <20220907172516.1210842-1-jiebin.sun@intel.com> <20220907143427.0ce54bbf096943ffca197fee@linux-foundation.org> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1662651543; a=rsa-sha256; cv=none; b=WGGk19YUig8OZSHiKYj1Il1EOX+8v/lEnzhvCnXAvMPV+YsVpOgk6J2DWKzFH108iXXPwJ j+9iVZQ+J0PKAahzDwYBwOnfmw2u7C/lyxvxIE3CCihXCgB80lV+m38kBJ9UWTJXchfJvI CP/K9paWGEYjKOUqAcm3WhOMPZFjRlI= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=VNj8EE9T; spf=pass (imf15.hostedemail.com: domain of akpm@linux-foundation.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1662651543; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=yEDDEp517YYzNNn7UeuJgnNhI2BekeSZAYp6JE4DnUk=; b=NbOXVTx4ECpyoRagOhbcX0rJqsY+9QkMt3WrIlyB3H6+nztg9NvNhaQExcQLMTS+ZCxJZi BwWsoC0CYitglutyLM7ueTIHVJ6C1K7T8n1Gy3godQ9kMuBL4kIQ9s9cdj2yMgs57fLWwi q/Kd0ysfQIFYwI6DEzw/CgDqS3c/0LM= X-Stat-Signature: wo5zqiuzjw3bqdhng436ijr7t1krpst6 X-Rspamd-Queue-Id: 7D3B0A0070 X-Rspamd-Server: rspam11 X-Rspam-User: Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=VNj8EE9T; spf=pass (imf15.hostedemail.com: domain of akpm@linux-foundation.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none X-HE-Tag: 1662651543-270916 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, 8 Sep 2022 16:25:47 +0800 "Sun, Jiebin" wrote: > In our case, if the local > percpu counter is near to INT_MAX and there comes a big msgsz, the > overflow issue could happen. percpu_counter_add_batch() handles this - your big message won't overflow an s64. Lookng at percpu_counter_add_batch(), is this tweak right? - don't need to update *fbc->counters inside the lock - that __this_cpu_sub() is an obscure way of zeroing the thing --- a/lib/percpu_counter.c~a +++ a/lib/percpu_counter.c @@ -89,8 +89,8 @@ void percpu_counter_add_batch(struct per unsigned long flags; raw_spin_lock_irqsave(&fbc->lock, flags); fbc->count += count; - __this_cpu_sub(*fbc->counters, count - amount); raw_spin_unlock_irqrestore(&fbc->lock, flags); + __this_cpu_write(*fbc->counters, 0); } else { this_cpu_add(*fbc->counters, amount); } _