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[209.85.167.51]) by smtp.gmail.com with ESMTPSA id z26sm2529043lja.125.2020.12.15.11.58.13 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Dec 2020 11:58:13 -0800 (PST) Received: by mail-lf1-f51.google.com with SMTP id y19so42512125lfa.13 for ; Tue, 15 Dec 2020 11:58:13 -0800 (PST) X-Received: by 2002:ac2:41d9:: with SMTP id d25mr11197984lfi.377.1608061956340; Tue, 15 Dec 2020 11:52:36 -0800 (PST) MIME-Version: 1.0 References: <20201214190237.a17b70ae14f129e2dca3d204@linux-foundation.org> <20201215030730.NC3CU98e4%akpm@linux-foundation.org> In-Reply-To: <20201215030730.NC3CU98e4%akpm@linux-foundation.org> From: Linus Torvalds Date: Tue, 15 Dec 2020 11:52:19 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [patch 075/200] mm: speedup mremap on 1GB or larger regions To: Andrew Morton Cc: almasrymina@google.com, "Aneesh Kumar K.V" , Anshuman Khandual , Arnd Bergmann , Brian Geffon , Borislav Petkov , Catalin Marinas , Christian Brauner , Dave Hansen , Frederic Weisbecker , gshan@redhat.com, hnaveed@wavecomp.com, Peter Anvin , John Hubbard , justin.he@arm.com, kaleshsingh@google.com, Kees Cook , "Kirill A . Shutemov" , Krzysztof Kozlowski , Linux-MM , linuxram@us.ibm.com, kernel test robot , Lokesh Gidra , Mark Rutland , Masahiro Yamada , Masami Hiramatsu , minchan@google.com, Ingo Molnar , mm-commits@vger.kernel.org, Peter Zijlstra , Ralph Campbell , Mike Rapoport , Sami Tolvanen , sandipan@linux.ibm.com, Shuah Khan , SeongJae Park , Steven Price , Suren Baghdasaryan , Thomas Gleixner , Will Deacon , ziy@nvidia.com Content-Type: text/plain; charset="UTF-8" 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 Mon, Dec 14, 2020 at 7:07 PM Andrew Morton wrote: > > From: Kalesh Singh > Subject: mm: speedup mremap on 1GB or larger regions > > Android needs to move large memory regions for garbage collection. The GC > requires moving physical pages of multi-gigabyte heap using mremap. > During this move, the application threads have to be paused for > correctness. It is critical to keep this pause as short as possible to > avoid jitters during user interaction. It would have been good to add a pointer to the PMD case we did earlier.. Also, a few comments on the actual performance in practice would be nice. Does this actually *trigger* on Android in practice? I can well imagine the PMD case triggering easily, but are there real-life Android loads that really do gigabyte heaps? That sounds a bit odd to me. So I don't have any complaints about the patch, but I just wonder how _realistic_ this actually is, particularly the alleged 13x improvement in timing... Linus