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 DAB66C433FE for ; Wed, 30 Nov 2022 02:23:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229777AbiK3CX7 (ORCPT ); Tue, 29 Nov 2022 21:23:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44602 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231314AbiK3CX6 (ORCPT ); Tue, 29 Nov 2022 21:23:58 -0500 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ADB256037F; Tue, 29 Nov 2022 18:23:50 -0800 (PST) Received: from canpemm500009.china.huawei.com (unknown [172.30.72.53]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4NMNFY6J5yzqSpv; Wed, 30 Nov 2022 10:19:45 +0800 (CST) Received: from [10.67.102.169] (10.67.102.169) by canpemm500009.china.huawei.com (7.192.105.203) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Wed, 30 Nov 2022 10:23:47 +0800 CC: , , , , , , , , , , , , , , , , , , , , , , , , Barry Song <21cnbao@gmail.com>, , , , Anshuman Khandual , Barry Song Subject: Re: [PATCH v7 1/2] mm/tlbbatch: Introduce arch_tlbbatch_should_defer() To: Andrew Morton References: <20221117082648.47526-1-yangyicong@huawei.com> <20221117082648.47526-2-yangyicong@huawei.com> <20221129152306.54b6d439e2a0ca7ece1d1afa@linux-foundation.org> From: Yicong Yang Message-ID: <9999b87d-5f7e-275b-d99f-b51ef19361eb@huawei.com> Date: Wed, 30 Nov 2022 10:23:47 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: <20221129152306.54b6d439e2a0ca7ece1d1afa@linux-foundation.org> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.102.169] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To canpemm500009.china.huawei.com (7.192.105.203) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On 2022/11/30 7:23, Andrew Morton wrote: > On Thu, 17 Nov 2022 16:26:47 +0800 Yicong Yang wrote: > >> From: Anshuman Khandual >> >> The entire scheme of deferred TLB flush in reclaim path rests on the >> fact that the cost to refill TLB entries is less than flushing out >> individual entries by sending IPI to remote CPUs. But architecture >> can have different ways to evaluate that. Hence apart from checking >> TTU_BATCH_FLUSH in the TTU flags, rest of the decision should be >> architecture specific. >> >> ... >> >> --- a/arch/x86/include/asm/tlbflush.h >> +++ b/arch/x86/include/asm/tlbflush.h >> @@ -240,6 +240,18 @@ static inline void flush_tlb_page(struct vm_area_struct *vma, unsigned long a) >> flush_tlb_mm_range(vma->vm_mm, a, a + PAGE_SIZE, PAGE_SHIFT, false); >> } >> >> +static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm) >> +{ >> + bool should_defer = false; >> + >> + /* If remote CPUs need to be flushed then defer batch the flush */ >> + if (cpumask_any_but(mm_cpumask(mm), get_cpu()) < nr_cpu_ids) >> + should_defer = true; >> + put_cpu(); >> + >> + return should_defer; >> +} >> + >> static inline u64 inc_mm_tlb_gen(struct mm_struct *mm) >> { >> /* >> diff --git a/mm/rmap.c b/mm/rmap.c >> index 2ec925e5fa6a..a9ab10bc0144 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -685,17 +685,10 @@ static void set_tlb_ubc_flush_pending(struct mm_struct *mm, bool writable) >> */ >> static bool should_defer_flush(struct mm_struct *mm, enum ttu_flags flags) >> { >> - bool should_defer = false; >> - >> if (!(flags & TTU_BATCH_FLUSH)) >> return false; >> >> - /* If remote CPUs need to be flushed then defer batch the flush */ >> - if (cpumask_any_but(mm_cpumask(mm), get_cpu()) < nr_cpu_ids) >> - should_defer = true; >> - put_cpu(); >> - >> - return should_defer; >> + return arch_tlbbatch_should_defer(mm); >> } > > I think this conversion could have been done better. > > should_defer_flush() is compiled if > CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH. So the patch implicitly > assumes that only x86 implements > CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH. Presently true, but what > happens if sparc (for example) wants to set > CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH? Now sparc needs its private > version of arch_tlbbatch_should_defer(), even if that is identical to > x86's. > The current logic is if architecture want to enable batched TLB flush, they need to implement their own version of arch_tlbbatch_should_defer() (for the hint to defer the TLB flush) and arch_tlbbatch_add_mm() (for pending TLB flush) and select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH. That's what we do in Patch 2/2 for enabling this on arm64. Since it is architecture specific, we must rely on the architecture to implement these two functions. Only select the ARCH_HAS_ARCH_TLBBATCH_SHOULD_DEFER is not enough. > Wouldn't it be better to make should_defer_flush() a __weak > function in rmap.c, or a static inline inside #ifndef > ARCH_HAS_ARCH_TLBBATCH_SHOULD_DEFER, or whatever technique best fits? > When ARCH_HAS_ARCH_TLBBATCH_SHOULD_DEFER is not selected, should_defer_flush() is implemented to only return false. I think this match what you want already. Thanks.