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=-4.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,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 3D3AFC433E0 for ; Tue, 9 Feb 2021 15:56:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ECED664E99 for ; Tue, 9 Feb 2021 15:56:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232565AbhBIP4r (ORCPT ); Tue, 9 Feb 2021 10:56:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60216 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232419AbhBIP4o (ORCPT ); Tue, 9 Feb 2021 10:56:44 -0500 Received: from mail-pl1-x636.google.com (mail-pl1-x636.google.com [IPv6:2607:f8b0:4864:20::636]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 80CDDC061574 for ; Tue, 9 Feb 2021 07:56:03 -0800 (PST) Received: by mail-pl1-x636.google.com with SMTP id x9so9981234plb.5 for ; Tue, 09 Feb 2021 07:56:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to; bh=RLLY3Kifgt8whTtEjTDT7sURhhrgrsnEjHhUvPN+ANU=; b=KwLsh6fpusewnWWexKKtZ5jK9Hz+r9MkMVjPSUeOQt4wtQLkbvzuUhMOL5jl7Nfc/3 3xsV/0Szxzec0zLgWs5FJiiZBR2J+Ggc3YMR5/zAJkSRTQXTR9Jv87X/Hpu5U0+0eP/l Ji2WPP0t56jRBYam45Zh/bsvYge+3jkhDuWkWpvYqel0M0e/CdFSHzNDbJiXp4n9Su0Q h6CzpVyyFaJNFGF2Z29LXZy/q5g5hxgImllBKNhmM7ea7e+JpoNz6BaCdF8+4DnbU9k9 0VJ8nL5hznLBuQ1p1YNgK0FyUuRRKZWBw8QZSCW3mv7Ai9IImnMIJVKs8vzBjKAIg7oH 2/yg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition :content-transfer-encoding:in-reply-to; bh=RLLY3Kifgt8whTtEjTDT7sURhhrgrsnEjHhUvPN+ANU=; b=Q1YxP0SF+fms75YPPvW5mfYxAX2zkVPmw+uSKHwDx3C3PSFHAz/9SvrEqbfqjTODti hATDfl2lfHhMGAXCeii6w2oXvq2lKjs8Wg+SR7rhNCeHFAn+lUk9el1VVJcdbcVOikba mge1uZdFlVuUNPnJSxYtHDAexHupqbyls99OV91QMhWuuCFSQ+4fxh47uqJxktQV5mlQ 4rweT6Z4iJniQ0KAI+EO0/UkF4N3WZACJIezA+RTvl4lDGdva8U9Gm6iqvgaiBvdNnXq aaCJZvnYS1tIj4kaMiAvbGe3fc+o1etb2TCXnNkqUtGzxjmQ4EvNr4NrRUd08C4hy/5P aEhw== X-Gm-Message-State: AOAM530RHK9buQXNgcLmhL9tvbsuQpSRj9+p9u4QYy9G1m2nA4xr3MRX MEJEc4FXWg8Ztl6GNytwncQ= X-Google-Smtp-Source: ABdhPJwY1X+a9UW2Q70a0LSbQJhTJ7xRLtjwcPyb7TRVW+yxStYhcyVczMFKyVTddKK48sBpTlWKFw== X-Received: by 2002:a17:90a:6589:: with SMTP id k9mr4618070pjj.100.1612886163051; Tue, 09 Feb 2021 07:56:03 -0800 (PST) Received: from google.com ([2620:15c:211:201:d107:fbfb:a7c8:913e]) by smtp.gmail.com with ESMTPSA id 25sm14762989pfh.199.2021.02.09.07.56.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Feb 2021 07:56:01 -0800 (PST) Sender: Minchan Kim Date: Tue, 9 Feb 2021 07:55:59 -0800 From: Minchan Kim To: Greg KH Cc: John Hubbard , Andrew Morton , linux-mm , LKML , surenb@google.com, joaodias@google.com, willy@infradead.org Subject: Re: [PATCH v2] mm: cma: support sysfs Message-ID: References: <20210208180142.2765456-1-minchan@kernel.org> <43cd6fc4-5bc5-50ec-0252-ffe09afd68ea@nvidia.com> <7cc229f4-609c-71dd-9361-063ef1bf7c73@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 09, 2021 at 07:56:30AM +0100, Greg KH wrote: > On Mon, Feb 08, 2021 at 10:34:51PM -0800, John Hubbard wrote: > > On 2/8/21 10:27 PM, John Hubbard wrote: > > > On 2/8/21 10:13 PM, Greg KH wrote: > > > > On Mon, Feb 08, 2021 at 05:57:17PM -0800, John Hubbard wrote: > > > > > On 2/8/21 3:36 PM, Minchan Kim wrote: > > > > > ... > > > > > > > >         char name[CMA_MAX_NAME]; > > > > > > > > +#ifdef CONFIG_CMA_SYSFS > > > > > > > > +    struct cma_stat    *stat; > > > > > > > > > > > > > > This should not be a pointer. By making it a pointer, you've added a bunch of pointless > > > > > > > extra code to the implementation. > > > > > > > > > > > > Originally, I went with the object lifetime with struct cma as you > > > > > > suggested to make code simple. However, Greg KH wanted to have > > > > > > release for kobj_type since it is consistent with other kboject > > > > > > handling. > > > > > > > > > > Are you talking about the kobj in your new struct cma_stat? That seems > > > > > like circular logic if so. I'm guessing Greg just wanted kobj methods > > > > > to be used *if* you are dealing with kobjects. That's a narrower point. > > > > > > > > > > I can't imagine that he would have insisted on having additional > > > > > allocations just so that kobj freeing methods could be used. :) > > > > > > > > Um, yes, I was :) > > > > > > > > You can not add a kobject to a structure and then somehow think you can > > > > just ignore the reference counting issues involved.  If a kobject is > > > > part of a structure then the kobject is responsible for controling the > > > > lifespan of the memory, nothing else can be. > > > > > > > > So by making the kobject dynamic, you properly handle that memory > > > > lifespan of the object, instead of having to worry about the lifespan of > > > > the larger object (which the original patch was not doing.) > > > > > > > > Does that make sense? > > > > > > > That part makes sense, yes, thanks. The part that I'm trying to straighten > > > out is, why was kobject even added to the struct cma_stat in the first > > > place? Why not just leave .stat as a static member variable, without > > > a kobject in it, and done? > > > > > > > Sorry, I think I get it now: this is in order to allow a separate lifetime > > for the .stat member. I was sort of implicitly assuming that the "right" > > way to do it is just have the whole object use one lifetime management, > > but as you say, there is no kobject being added to the parent. > > > > I still feel odd about the allocation and freeing of something that seems > > to be logically the same lifetime (other than perhaps a few, briefly pending > > sysfs reads, at the end of life). So I'd still think that the kobject should > > be added to the parent... sruct cma_stat { spinlock_t lock; unsigned long pages_attemtp; unsigned long pages_fail; }; struct cma { .. .. struct kobject kobj; struct cma_stat stat; }; I guess this is what Johan suggested. I agree with it. > > That's fine if you want to add it to the parent. If so, then the > kobject controls the lifetime of the structure, nothing else can. The problem was parent object(i.e., struct cma cma_areas) is static arrary so kobj->release function will be NULL or just dummy. Is it okay? I thought it was one of the what you wanted to avoid it. > > Either is fine with me, what is "forbidden" is having a kobject and > somehow thinking that it does not control the lifetime of the structure. Since parent object is static arrary, there is no need to control the lifetime so I am curious if parent object approach is okay from kobject handling point of view. If it's no problem, I am happy to change it.