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[142.162.115.133]) by smtp.gmail.com with ESMTPSA id f188sm4392003qkj.110.2021.02.18.09.32.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Feb 2021 09:32:01 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1lCn9k-00B5jy-Tc; Thu, 18 Feb 2021 13:32:00 -0400 Date: Thu, 18 Feb 2021 13:32:00 -0400 From: Jason Gunthorpe To: Zi Yan Cc: Matthew Wilcox , Andrew Morton , Mike Kravetz , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Davidlohr Bueso , "Kirill A . Shutemov" , Andrea Arcangeli , Oscar Salvador , Joao Martins , stable@vger.kernel.org Subject: Re: [PATCH 1/2] hugetlb: fix update_and_free_page contig page struct assumption Message-ID: <20210218173200.GA2643399@ziepe.ca> References: <20210217184926.33567-1-mike.kravetz@oracle.com> <20210217110252.185c7f5cd5a87c3f7b0c0144@linux-foundation.org> <20210218144554.GS2858050@casper.infradead.org> <20210218172500.GA4718@ziepe.ca> <19612088-4856-4BE9-A731-BB903511F352@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <19612088-4856-4BE9-A731-BB903511F352@nvidia.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 18, 2021 at 12:27:58PM -0500, Zi Yan wrote: > On 18 Feb 2021, at 12:25, Jason Gunthorpe wrote: > > > On Thu, Feb 18, 2021 at 02:45:54PM +0000, Matthew Wilcox wrote: > >> On Wed, Feb 17, 2021 at 11:02:52AM -0800, Andrew Morton wrote: > >>> On Wed, 17 Feb 2021 10:49:25 -0800 Mike Kravetz wrote: > >>>> page structs are not guaranteed to be contiguous for gigantic pages. The > >>> > >>> June 2014. That's a long lurk time for a bug. I wonder if some later > >>> commit revealed it. > >> > >> I would suggest that gigantic pages have not seen much use. Certainly > >> performance with Intel CPUs on benchmarks that I've been involved with > >> showed lower performance with 1GB pages than with 2MB pages until quite > >> recently. > > > > I suggested in another thread that maybe it is time to consider > > dropping this "feature" > > You mean dropping gigantic page support in hugetlb? No, I mean dropping support for arches that want to do: tail_page != head_page + tail_page_nr because they can't allocate the required page array either virtually or physically contiguously. It seems like quite a burden on the core mm for a very niche, and maybe even non-existant, case. It was originally done for PPC, can these PPC systems use VMEMMAP now? > > The cost to fix GUP to be compatible with this will hurt normal > > GUP performance - and again, that nobody has hit this bug in GUP > > further suggests the feature isn't used.. > > A easy fix might be to make gigantic hugetlb page depends on > CONFIG_SPARSEMEM_VMEMMAP, which guarantee all struct pages are contiguous. Yes, exactly. Jason