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[209.132.183.28]) by mx.google.com with ESMTPS id q46si130532qtf.237.2019.03.28.18.01.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 28 Mar 2019 18:01:03 -0700 (PDT) Received-SPF: pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jglisse@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D239088ABB; Fri, 29 Mar 2019 01:01:02 +0000 (UTC) Received: from redhat.com (ovpn-121-118.rdu2.redhat.com [10.10.121.118]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BE88362669; Fri, 29 Mar 2019 01:01:01 +0000 (UTC) Date: Thu, 28 Mar 2019 21:00:59 -0400 From: Jerome Glisse To: Ira Weiny Cc: John Hubbard , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Dan Williams Subject: Re: [PATCH v2 02/11] mm/hmm: use reference counting for HMM struct v2 Message-ID: <20190329010059.GB16680@redhat.com> References: <20190325144011.10560-1-jglisse@redhat.com> <20190325144011.10560-3-jglisse@redhat.com> <20190328110719.GA31324@iweiny-DESK2.sc.intel.com> <20190328191122.GA5740@redhat.com> <20190328212145.GA13560@redhat.com> <20190328165708.GH31324@iweiny-DESK2.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190328165708.GH31324@iweiny-DESK2.sc.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Fri, 29 Mar 2019 01:01:02 +0000 (UTC) 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, Mar 28, 2019 at 09:57:09AM -0700, Ira Weiny wrote: > On Thu, Mar 28, 2019 at 05:39:26PM -0700, John Hubbard wrote: > > On 3/28/19 2:21 PM, Jerome Glisse wrote: > > > On Thu, Mar 28, 2019 at 01:43:13PM -0700, John Hubbard wrote: > > >> On 3/28/19 12:11 PM, Jerome Glisse wrote: > > >>> On Thu, Mar 28, 2019 at 04:07:20AM -0700, Ira Weiny wrote: > > >>>> On Mon, Mar 25, 2019 at 10:40:02AM -0400, Jerome Glisse wrote: > > >>>>> From: Jérôme Glisse > > [...] > > >>>>> @@ -67,14 +78,9 @@ struct hmm { > > >>>>> */ > > >>>>> static struct hmm *hmm_register(struct mm_struct *mm) > > >>>>> { > > >>>>> - struct hmm *hmm = READ_ONCE(mm->hmm); > > >>>>> + struct hmm *hmm = mm_get_hmm(mm); > > >>>> > > >>>> FWIW: having hmm_register == "hmm get" is a bit confusing... > > >>> > > >>> The thing is that you want only one hmm struct per process and thus > > >>> if there is already one and it is not being destroy then you want to > > >>> reuse it. > > >>> > > >>> Also this is all internal to HMM code and so it should not confuse > > >>> anyone. > > >>> > > >> > > >> Well, it has repeatedly come up, and I'd claim that it is quite > > >> counter-intuitive. So if there is an easy way to make this internal > > >> HMM code clearer or better named, I would really love that to happen. > > >> > > >> And we shouldn't ever dismiss feedback based on "this is just internal > > >> xxx subsystem code, no need for it to be as clear as other parts of the > > >> kernel", right? > > > > > > Yes but i have not seen any better alternative that present code. If > > > there is please submit patch. > > > > > > > Ira, do you have any patch you're working on, or a more detailed suggestion there? > > If not, then I might (later, as it's not urgent) propose a small cleanup patch > > I had in mind for the hmm_register code. But I don't want to duplicate effort > > if you're already thinking about it. > > No I don't have anything. > > I was just really digging into these this time around and I was about to > comment on the lack of "get's" for some "puts" when I realized that > "hmm_register" _was_ the get... > > :-( > The get is mm_get_hmm() were you get a reference on HMM from a mm struct. John in previous posting complained about me naming that function hmm_get() and thus in this version i renamed it to mm_get_hmm() as we are getting a reference on hmm from a mm struct. The hmm_put() is just releasing the reference on the hmm struct. Here i feel i am getting contradicting requirement from different people. I don't think there is a way to please everyone here. Cheers, Jérôme