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Wed, 13 Aug 2025 13:06:25 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHTvuKixXYylw6jZAk9WOPy5ESjWCqWkg0b02ZWazA25ZrJ13LuOVgPLfrU/sj8o6PUC9anPA== X-Received: by 2002:a05:6214:c41:b0:707:69ad:d84a with SMTP id 6a1803df08f44-70af5c31faemr8221766d6.42.1755115585490; Wed, 13 Aug 2025 13:06:25 -0700 (PDT) Received: from x1.local ([174.89.135.171]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-70af5b0ed60sm2678236d6.45.2025.08.13.13.06.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Aug 2025 13:06:24 -0700 (PDT) Date: Wed, 13 Aug 2025 16:06:12 -0400 From: Peter Xu To: Lokesh Gidra Cc: akpm@linux-foundation.org, aarcange@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, 21cnbao@gmail.com, ngeoffray@google.com, Suren Baghdasaryan , Kalesh Singh , Barry Song , David Hildenbrand Subject: Re: [PATCH v5] userfaultfd: opportunistic TLB-flush batching for present pages in MOVE Message-ID: References: <20250813193024.2279805-1-lokeshgidra@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250813193024.2279805-1-lokeshgidra@google.com> On Wed, Aug 13, 2025 at 12:30:24PM -0700, Lokesh Gidra wrote: > MOVE ioctl's runtime is dominated by TLB-flush cost, which is required > for moving present pages. Mitigate this cost by opportunistically > batching present contiguous pages for TLB flushing. > > Without batching, in our testing on an arm64 Android device with UFFD GC, > which uses MOVE ioctl for compaction, we observed that out of the total > time spent in move_pages_pte(), over 40% is in ptep_clear_flush(), and > ~20% in vm_normal_folio(). > > With batching, the proportion of vm_normal_folio() increases to over > 70% of move_pages_pte() without any changes to vm_normal_folio(). > Furthermore, time spent within move_pages_pte() is only ~20%, which > includes TLB-flush overhead. > > When the GC intensive benchmark, which was used to gather the above > numbers, is run on cuttlefish (qemu android instance on x86_64), the > completion time of the benchmark went down from ~45mins to ~20mins. > > Furthermore, system_server, one of the most performance critical system > processes on android, saw over 50% reduction in GC compaction time on an > arm64 android device. > > Cc: Suren Baghdasaryan > Cc: Kalesh Singh > Cc: Barry Song > Cc: David Hildenbrand > Cc: Peter Xu > Signed-off-by: Lokesh Gidra Acked-by: Peter Xu -- Peter Xu