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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 51B32C07CA9 for ; Tue, 28 Nov 2023 11:15:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344531AbjK1LPT (ORCPT ); Tue, 28 Nov 2023 06:15:19 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56842 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344124AbjK1LPR (ORCPT ); Tue, 28 Nov 2023 06:15:17 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 14E45D60 for ; Tue, 28 Nov 2023 03:15:24 -0800 (PST) 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > >