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[142.162.115.133]) by smtp.gmail.com with ESMTPSA id 196sm1758474qkn.64.2021.02.03.06.53.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Feb 2021 06:53:14 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1l7JWr-0031OU-H2; Wed, 03 Feb 2021 10:53:13 -0400 Date: Wed, 3 Feb 2021 10:53:13 -0400 From: Jason Gunthorpe To: Joao Martins Cc: Pavel Tatashin , linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, vbabka@suse.cz, mhocko@suse.com, david@redhat.com, osalvador@suse.de, dan.j.williams@intel.com, sashal@kernel.org, tyhicks@linux.microsoft.com, iamjoonsoo.kim@lge.com, mike.kravetz@oracle.com, rostedt@goodmis.org, mingo@redhat.com, peterz@infradead.org, mgorman@suse.de, willy@infradead.org, rientjes@google.com, jhubbard@nvidia.com, linux-doc@vger.kernel.org, ira.weiny@intel.com, linux-kselftest@vger.kernel.org, jmorris@namei.org Subject: Re: [PATCH v8 02/14] mm/gup: check every subpage of a compound page during isolation Message-ID: <20210203145313.GQ4718@ziepe.ca> References: <20210125194751.1275316-1-pasha.tatashin@soleen.com> <20210125194751.1275316-3-pasha.tatashin@soleen.com> <05a66361-214c-2afe-22e4-12862ea1e4e2@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <05a66361-214c-2afe-22e4-12862ea1e4e2@oracle.com> 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, Feb 03, 2021 at 01:22:18PM +0000, Joao Martins wrote: > With this, longterm gup will 'regress' for hugetlbfs e.g. from ~6k -> 32k usecs when > pinning a 16G hugetlb file. Yes, but correctness demands it. The solution is to track these pages as we discover them so we know if a PMD/PUD points and can directly skip the duplicated work > Splitting can only occur on THP right? If so, perhaps we could > retain the @step increment for compound pages but when > !is_transparent_hugepage(head) or just PageHuge(head) like: Honestly I'd rather see it fixed properly which will give even bigger performance gains - avoiding the entire rescan of the page list will be a win Jason