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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id c1sm331693qta.86.2020.09.02.12.57.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Sep 2020 12:57:39 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kDYt1-0065rX-4P; Wed, 02 Sep 2020 16:57:39 -0300 Date: Wed, 2 Sep 2020 16:57:39 -0300 From: Jason Gunthorpe To: Zi Yan Cc: linux-mm@kvack.org, Roman Gushchin , Rik van Riel , "Kirill A . Shutemov" , Matthew Wilcox , Shakeel Butt , Yang Shi , David Nellans , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 00/16] 1GB THP support on x86_64 Message-ID: <20200902195739.GI24045@ziepe.ca> References: <20200902180628.4052244-1-zi.yan@sent.com> <20200902184053.GF24045@ziepe.ca> <20200902184852.GH24045@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: BDA8F18140B60 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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 Wed, Sep 02, 2020 at 03:05:39PM -0400, Zi Yan wrote: > On 2 Sep 2020, at 14:48, Jason Gunthorpe wrote: > > > On Wed, Sep 02, 2020 at 02:45:37PM -0400, Zi Yan wrote: > > > >>> Surprised this doesn't touch mm/pagewalk.c ? > >> > >> 1GB PUD page support is present for DAX purpose, so the code is there > >> in mm/pagewalk.c already. I only needed to supply ops->pud_entry when using > >> the functions in mm/pagewalk.c. :) > > > > Yes, but doesn't this change what is possible under the mmap_sem > > without the page table locks? > > > > ie I would expect some thing like pmd_trans_unstable() to be required > > as well for lockless walkers. (and I don't think the pmd code is 100% > > right either) > > > > Right. I missed that. Thanks for pointing it out. > The code like this, right? Technically all those *pud's are racy too, the design here with the _unstable function call always seemed weird. I strongly suspect it should mirror how get_user_pages_fast works for lockless walking Jason