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[216.228.121.143]) by mx.google.com with ESMTPS id r6si2468909pfn.165.2019.03.29.13.07.46 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 29 Mar 2019 13:07:46 -0700 (PDT) Received-SPF: pass (google.com: domain of jhubbard@nvidia.com designates 216.228.121.143 as permitted sender) client-ip=216.228.121.143; Authentication-Results: mx.google.com; dkim=pass header.i=@nvidia.com header.s=n1 header.b=eX2VKtNM; spf=pass (google.com: domain of jhubbard@nvidia.com designates 216.228.121.143 as permitted sender) smtp.mailfrom=jhubbard@nvidia.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=nvidia.com Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqemgate14.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Fri, 29 Mar 2019 13:07:49 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Fri, 29 Mar 2019 13:07:45 -0700 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Fri, 29 Mar 2019 13:07:45 -0700 Received: from [10.110.48.28] (172.20.13.39) by HQMAIL101.nvidia.com (172.20.187.10) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Fri, 29 Mar 2019 20:07:45 +0000 Subject: Re: [PATCH v2 02/11] mm/hmm: use reference counting for HMM struct v2 To: Jerome Glisse , Ira Weiny CC: , , Andrew Morton , Dan Williams References: <20190328110719.GA31324@iweiny-DESK2.sc.intel.com> <20190328191122.GA5740@redhat.com> <20190328212145.GA13560@redhat.com> <20190328165708.GH31324@iweiny-DESK2.sc.intel.com> <20190329010059.GB16680@redhat.com> <55dd8607-c91b-12ab-e6d7-adfe6d9cb5e2@nvidia.com> <20190329015003.GE16680@redhat.com> <20190328182100.GJ31324@iweiny-DESK2.sc.intel.com> <20190329022519.GJ16680@redhat.com> From: John Hubbard X-Nvconfidentiality: public Message-ID: <144f034d-9688-5aad-7b68-34e1d4b08228@nvidia.com> Date: Fri, 29 Mar 2019 13:07:45 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.3 MIME-Version: 1.0 In-Reply-To: <20190329022519.GJ16680@redhat.com> X-Originating-IP: [172.20.13.39] X-ClientProxiedBy: HQMAIL106.nvidia.com (172.18.146.12) To HQMAIL101.nvidia.com (172.20.187.10) Content-Type: text/plain; charset="utf-8" Content-Language: en-US-large Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1553890069; bh=GSqEMrrxwhxreIUm3fGaxmGkN2Y6WWPBPr8DyC7ajdk=; h=X-PGP-Universal:Subject:To:CC:References:From:X-Nvconfidentiality: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=eX2VKtNMLTYQHApWKfo7Py4nw6DR6FufYnyTH7xN4/q7QHLQD4wa6pyTXQ8yQIOxu 37jg/uGN19UB4Wnf8zGU0jz9+URnrPDJSCGL9ii8yJY9Vd67CKrmaaZwfpkeZ8tfmA +7IoQ7vzHyMuQFJ9ClsU8RL0znbOjUymNa8Iza2TeqQhpdRkpajBzGilV2Q4RYimLW FcPW5d8bhLF395MQsSi15im16UUj2Lw4cKorTKdV6+ahGKIMcQvEupqXqogfjsvFaY MLRyJC2y/5BmmZcUvpqJDq+6eLiALwHMWLJ7YoBVuarVFIoavfG2Ln8j4ur9eM4CdS j+rDjaJoVGyJQ== 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 3/28/19 7:25 PM, Jerome Glisse wrote: [...] >> The input value is not the problem. The problem is in the naming. >> >> obj = get_obj( various parameters ); >> put_obj(obj); >> >> >> The problem is that the function is named hmm_register() either "gets" a >> reference to _or_ creates and gets a reference to the hmm object. >> >> What John is probably ready to submit is something like. >> >> struct hmm *get_create_hmm(struct mm *mm); >> void put_hmm(struct hmm *hmm); >> >> >> So when you are reading the code you see... >> >> foo(...) { >> struct hmm *hmm = get_create_hmm(mm); >> >> if (!hmm) >> error... >> >> do stuff... >> >> put_hmm(hmm); >> } >> >> Here I can see a very clear get/put pair. The name also shows that the hmm is >> created if need be as well as getting a reference. >> > > You only need to create HMM when you either register a mirror or > register a range. So they two pattern: > > average_foo() { > struct hmm *hmm = mm_get_hmm(mm); > ... > hmm_put(hmm); > } > > register_foo() { > struct hmm *hmm = hmm_register(mm); > ... > return 0; > error: > ... > hmm_put(hmm); > } > 1. Looking at this fresh this morning, Ira's idea of just a single rename actually clarifies things a lot more than I expected. I think the following tiny patch would suffice here (I've updated documentation to match, and added a missing "@Return:" line too): iff --git a/mm/hmm.c b/mm/hmm.c index fd143251b157..37b1c5803f1e 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -50,14 +50,17 @@ static inline struct hmm *mm_get_hmm(struct mm_struct *mm) } /* - * hmm_register - register HMM against an mm (HMM internal) + * hmm_get_create - returns an HMM object, either by referencing the existing + * (per-process) object, or by creating a new one. * - * @mm: mm struct to attach to + * @mm: the mm_struct to attach to + * @Return: a pointer to the HMM object, or NULL upon failure. This pointer must + * be released, when done, via hmm_put(). * - * This is not intended to be used directly by device drivers. It allocates an - * HMM struct if mm does not have one, and initializes it. + * This is an internal HMM function, and is not intended to be used directly by + * device drivers. */ -static struct hmm *hmm_register(struct mm_struct *mm) +static struct hmm *hmm_get_create(struct mm_struct *mm) { struct hmm *hmm = mm_get_hmm(mm); bool cleanup = false; @@ -288,7 +291,7 @@ int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm) if (!mm || !mirror || !mirror->ops) return -EINVAL; - mirror->hmm = hmm_register(mm); + mirror->hmm = hmm_get_create(mm); if (!mirror->hmm) return -ENOMEM; @@ -915,7 +918,7 @@ int hmm_range_register(struct hmm_range *range, range->start = start; range->end = end; - range->hmm = hmm_register(mm); + range->hmm = hmm_get_create(mm); if (!range->hmm) return -EFAULT; 2. A not directly related point: did you see my minor comment on patch 0001? I think it might have been missed in all the threads yesterday. thanks, -- John Hubbard NVIDIA