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[209.132.183.28]) by mx.google.com with ESMTPS id l26si37713558qkg.62.2019.08.01.08.04.36 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 01 Aug 2019 08:04:36 -0700 (PDT) Received-SPF: pass (google.com: domain of oleg@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of oleg@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=oleg@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D034B30A9234; Thu, 1 Aug 2019 15:04:35 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.136]) by smtp.corp.redhat.com (Postfix) with SMTP id 0F0E51992D; Thu, 1 Aug 2019 15:04:33 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 1 Aug 2019 17:04:35 +0200 (CEST) Date: Thu, 1 Aug 2019 17:04:33 +0200 From: Oleg Nesterov To: Song Liu Cc: lkml , "linux-mm@kvack.org" , "akpm@linux-foundation.org" , "matthew.wilcox@oracle.com" , "kirill.shutemov@linux.intel.com" , Kernel Team , "william.kucharski@oracle.com" , "srikar@linux.vnet.ibm.com" Subject: Re: [PATCH v10 3/4] mm, thp: introduce FOLL_SPLIT_PMD Message-ID: <20190801150432.GC31538@redhat.com> References: <20190730052305.3672336-1-songliubraving@fb.com> <20190730052305.3672336-4-songliubraving@fb.com> <20190730161113.GC18501@redhat.com> <1E2B5653-BA85-4A05-9B41-57CF9E48F14A@fb.com> <20190731151842.GB25078@redhat.com> <04FB43C3-6E2B-4868-B9D5-C00342DA5C6F@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <04FB43C3-6E2B-4868-B9D5-C00342DA5C6F@fb.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Thu, 01 Aug 2019 15:04:35 +0000 (UTC) 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 07/31, Song Liu wrote: > > > On Jul 31, 2019, at 8:18 AM, Oleg Nesterov wrote: > > > > Now, I don't understand why do we need pmd_trans_unstable() after > > split_huge_pmd(huge-zero-pmd), but whatever reason we have, why can't we > > unify both cases? > > > > IOW, could you explain why the path below is wrong? > > I _think_ the following patch works (haven't fully tested yet). But I am not > sure whether this is the best. By separating the two cases, we don't duplicate > much code. And it is clear that the two cases are handled differently. > Therefore, I would prefer to keep these separate for now. I disagree. I think this separation makes the code less readable/understandable. Exactly because it handles two cases differently and it is absolutely not clear why. But I can't argue, please forget. Oleg.