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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 25272C433FE for ; Wed, 30 Nov 2022 02:23:56 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B38CB6B0072; Tue, 29 Nov 2022 21:23:55 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id AE96B6B0073; Tue, 29 Nov 2022 21:23:55 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9B13C6B0074; Tue, 29 Nov 2022 21:23:55 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 88A2B6B0072 for ; Tue, 29 Nov 2022 21:23:55 -0500 (EST) Received: from smtpin23.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 5725CC0572 for ; Wed, 30 Nov 2022 02:23:55 +0000 (UTC) X-FDA: 80188513230.23.70B88E7 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by imf08.hostedemail.com (Postfix) with ESMTP id 8A36616000F for ; Wed, 30 Nov 2022 02:23:53 +0000 (UTC) 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 ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1669775035; a=rsa-sha256; cv=none; b=g8OB1P26jZbD0E/zKbV39Qhoj8yET8/7YtIfY5+WTVXKQxoqgt1rT1XtQl7E4L5ygnsEVu DCPKxakB9Ufx32i+vtHDOt4NfunHEtjaqrug4veA17oh4eS+jjQqRDzWmnqKsJC8woN7qj z8pgjkcmOz7K0XuOHZGBas4JQyijcqk= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf08.hostedemail.com: domain of yangyicong@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=yangyicong@huawei.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1669775035; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=htqXI+AUo28DxXdqLa24BV3ea6N8ZDRe7iGk1T3L1Do=; b=IuY8CuFB3zY89KSlyyO7B89F1Jvpz+SbUoJSakPy81Cm1/1TQvUb2OHiWnkMyq8bXjbpSK aMmI6+QHxd5bnFYFuoJD7TCcwMqLkHW/rPEv2kCFjt7fth0vCD9+PXYosEYJkQRYdiWwpX 13JWJv7AgyhVnhaafauL5AntWJ9v5kk= X-Stat-Signature: rmak8ucwizjn3qipz3k136dou4uojapm Authentication-Results: imf08.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf08.hostedemail.com: domain of yangyicong@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=yangyicong@huawei.com X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 8A36616000F X-Rspam-User: X-HE-Tag: 1669775033-105278 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 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.