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=-5.8 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 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 58752C433E6 for ; Mon, 11 Jan 2021 18:12:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2A9E1229CA for ; Mon, 11 Jan 2021 18:12:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390198AbhAKSML (ORCPT ); Mon, 11 Jan 2021 13:12:11 -0500 Received: from mail.kernel.org ([198.145.29.99]:37214 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389269AbhAKSMK (ORCPT ); Mon, 11 Jan 2021 13:12:10 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 5FF102250E; Mon, 11 Jan 2021 18:11:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1610388690; bh=cBq1y0iMkVTuLGtG1DMGGNgPvj5YM9W4o39IMIcR/EM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=sxqXv2rUHSZzxBPXqzFkyl5mxoaAoc95Zt4psMjmeQo2CVASu06pc9ol5BQ3vvgGd uZeYPFWpeQr6hEt/aV+Ch9VuNfNKHdab3BHBciV142h7zVWwQygpcAHvOI2vR9sdkx RoQBiqRpwhIL3nOxhiTVDGU0+zKdm3KU7jABUgZo= Date: Mon, 11 Jan 2021 19:11:25 +0100 From: Greg KH To: Matthew Wilcox Cc: Christoph Hellwig , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] char_dev: replace cdev_map with an xarray Message-ID: References: <20210111170513.1526780-1-hch@lst.de> <20210111173500.GG35215@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210111173500.GG35215@casper.infradead.org> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Jan 11, 2021 at 05:35:00PM +0000, Matthew Wilcox wrote: > On Mon, Jan 11, 2021 at 06:05:13PM +0100, Christoph Hellwig wrote: > > None of the complicated overlapping regions bits of the kobj_map are > > required for the character device lookup, so just a trivial xarray > > instead. > > Thanks for doing this. We could make it more efficient for chardevs > that occupy 64 or more consecutive/aligned devices -- is it worth doing? efficient in what way? Space or faster lookup? THis shouldn't be on a "fast" lookup path, so I doubt that's worth optimizing for. Space, maybe, for systems with thousands of scsi devices, but usually they just stick to the block device, not a char device from what I remember. thanks, greg k-h