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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 F2940C3A5A8 for ; Tue, 3 Sep 2019 06:52:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C9D9E23401 for ; Tue, 3 Sep 2019 06:52:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="D0b65z2+" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726481AbfICGv6 (ORCPT ); Tue, 3 Sep 2019 02:51:58 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:46744 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725878AbfICGv6 (ORCPT ); Tue, 3 Sep 2019 02:51:58 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=on1uS5ivzDuDh9bGgt6qOTnzv59PRDx52jliN2T4+Mo=; b=D0b65z2+nz0bUijDBcAL7blia KGLhVDc4Bdpo5lTzExmOhVr6xcJ2Q+FEcYmgis7Z+mT3YXjEKHrdOE6xtmUosvth6cQmx351LlTdX Oie7o3eEP0PPc3WI2mZgGxxG+SIeSAg4YcnUPvAbSEaU3tM2CKCOt3mPf//OU3S/2b4EyCcExd5iE MVatl0Xr+stxlGWhhU1eIa3vDxYN2DMNOU/2dDuWoopMnSmuO6xBYiS8tGW/ui5HecpjB3+/EYHJJ 7mBAXGBk124z43eTlwevOFs8Xwhu/p8WDiozAB2gIVMbf6UFZKqvb2b33/tNQ3haEPeGPhb8ip4VS l59g+y2lA==; Received: from hch by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1i52fT-0007ew-Ft; Tue, 03 Sep 2019 06:51:55 +0000 Date: Mon, 2 Sep 2019 23:51:55 -0700 From: Christoph Hellwig To: Alexey Dobriyan Cc: mingo@redhat.com, peterz@infradead.org, aarcange@redhat.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, rcu@vger.kernel.org, dm-devel@redhat.com, axboe@kernel.dk Subject: Re: [dm-devel] [PATCH] sched: make struct task_struct::state 32-bit Message-ID: <20190903065155.GA28322@infradead.org> References: <20190902210558.GA23013@avx2> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190902210558.GA23013@avx2> User-Agent: Mutt/1.11.4 (2019-03-13) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Tue, Sep 03, 2019 at 12:05:58AM +0300, Alexey Dobriyan wrote: > 32-bit accesses are shorter than 64-bit accesses on x86_64. > Nothing uses 64-bitness of ->state. > > Space savings are ~2KB on F30 kernel config. I guess we'd save even more when moving from a volatile to WRITE_ONCE/READ_ONCE..