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imf30.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf30.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1701170125; a=rsa-sha256; cv=none; b=qiEWsZvZIiAzdZSDAL/uH4X9jryZ/iO+3hKv9Rs5lIjJrrvA0HDwaybvmUveDooWFdXFqN KJDWauGnVa3h75wvJmQbd/kr9tuNkhBaKJb4mjQDw7DCg4WbFDWlXJPUZzaUxXQP6YG9dG 2IChRyf+uelrS01uIdovwacymhl8Y90= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 48454C15; Tue, 28 Nov 2023 03:16:11 -0800 (PST) Received: from [10.1.33.188] (XHFQ2J9959.cambridge.arm.com [10.1.33.188]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B4A923F73F; Tue, 28 Nov 2023 03:15:20 -0800 (PST) Message-ID: <51f57fa1-a2ca-4e3e-82cd-b0733d4f12a7@arm.com> Date: Tue, 28 Nov 2023 11:15:19 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 14/14] arm64/mm: Add ptep_get_and_clear_full() to optimize process teardown Content-Language: en-GB To: Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, andreyknvl@gmail.com, anshuman.khandual@arm.com, ardb@kernel.org, catalin.marinas@arm.com, david@redhat.com, dvyukov@google.com, glider@google.com, james.morse@arm.com, jhubbard@nvidia.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mark.rutland@arm.com, maz@kernel.org, oliver.upton@linux.dev, ryabinin.a.a@gmail.com, suzuki.poulose@arm.com, vincenzo.frascino@arm.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yuzenghui@huawei.com, yuzhao@google.com, ziy@nvidia.com References: <20231115163018.1303287-15-ryan.roberts@arm.com> <20231128073254.37870-1-v-songbaohua@oppo.com> From: Ryan Roberts In-Reply-To: <20231128073254.37870-1-v-songbaohua@oppo.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: E00AB80003 X-Stat-Signature: gcajwm8iej4kghfqei5bo9o7yfsm4563 X-Rspam-User: X-HE-Tag: 1701170124-992877 X-HE-Meta: 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 cKEcXphF yzbM7/ex935UBGyOhgC2JpiMpu4P/thsEx1Qrw5JZ3bXUp8aI8iyH0+SS0G7esZ3CeGimSonSTbi6FCQSta9QYXjEtyAny4L3BFSax7p6T4y4tC551xk0+k8/fDfxolEKD+Pz2zo7Iesx7EFx7hpunRkqpczlebjrAhVqJMflmrztqh4ojSUgkR3TAcPSmywqDdECbu/UAwelIK9+FCUFisuemxV8FAE7F0/x1P28iZPMRRVQWddzfcfabIFYv6c21deRt8Fx3F7+Fmw= 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: List-Subscribe: List-Unsubscribe: On 28/11/2023 07:32, Barry Song wrote: >> +#define __HAVE_ARCH_PTEP_GET_AND_CLEAR_FULL >> +static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm, >> + unsigned long addr, pte_t *ptep, int full) >> +{ >> + pte_t orig_pte = __ptep_get(ptep); >> + >> + if (!pte_valid_cont(orig_pte) || !full) { >> + contpte_try_unfold(mm, addr, ptep, orig_pte); >> + return __ptep_get_and_clear(mm, addr, ptep); >> + } else >> + return contpte_ptep_get_and_clear_full(mm, addr, ptep); >> +} >> + > > Hi Ryan, > > I feel quite hard to understand the code. when !pte_valid_cont(orig_pte), > we will call contpte_try_unfold(mm, addr, ptep, orig_pte); > > but in contpte_try_unfold(), we call unfold only if pte_valid_cont() > is true: > static inline void contpte_try_unfold(struct mm_struct *mm, unsigned long addr, > pte_t *ptep, pte_t pte) > { > if (contpte_is_enabled(mm) && pte_valid_cont(pte)) > __contpte_try_unfold(mm, addr, ptep, pte); > } > > so do you mean the below? > > if (!pte_valid_cont(orig_pte)) > return __ptep_get_and_clear(mm, addr, ptep); > > if (!full) { > contpte_try_unfold(mm, addr, ptep, orig_pte); > return __ptep_get_and_clear(mm, addr, ptep); > } else { > return contpte_ptep_get_and_clear_full(mm, addr, ptep); > } Yes, this is equivalent. In general, I was trying not to spray `if (pte_valid_cont(orig_pte))` checks everywhere to guard contpte_try_unfold() and instead put the checks into contpte_try_unfold() (hence the 'try'). I figured just calling it unconditionally and letting the compiler optimize as it sees fit was the cleanest approach. But in this instance I can see this is confusing. I'll modify as you suggest. Thanks! > > Thanks > Barry > >