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AJvYcCU+IN+YUQ3WM4eZR0P0N3oo69GhxxDM5BiI8wk5iLYBxv7OWgcnicN2tZ6Fcjqrij9M5HrW3wFNzA==@kvack.org X-Gm-Message-State: AOJu0YzcubNml6jjUD/KARYrMn1biOlLqUiAIS0xbfqRVNooodGW9yzZ JVr2ZmHv+RyhceRHQ8Iyh9C5wvwkFV9j+SJVM0L1qg1EP2rrvMf7Wke0M8ATI5FDObRNOCuYHrx 1Stky9RHqHBQ7s+EnyCWX6nMo9fpd55fx6TacAXcO X-Gm-Gg: ASbGnct52b4au0eMyHK+m2aXCiEFYdH2Nle6ck547twIbvWt05e4c9yL1hWyxdy3LEX A1yxhzZ7OTl8gSmu5p24pGbWM5e70e7TdSG930hE07fFeeXWPJGkR9DLdjLUx03n3HVXUV3v847 L/hjvJB8ArQrDVyYWrjppVAAcxg/QgNM3kl8VO68Nfy8qB6ntpMZrJ6F9D72XSAouHRuEVJj/gL Tv8z+tpbdt5SWfejy5Wxu22mH7hldp7u/mfkSsy X-Google-Smtp-Source: AGHT+IGeVXfDi+GOeKEOGwGKfuGKlGjEf7ZPtGH8NAet/PE11DWKQCepuum1A6pr1DfJRUVQTFJrixrJo9wirRpXH3Y= X-Received: by 2002:aa7:c68f:0:b0:617:e6b2:1fda with SMTP id 4fb4d7f45d1cf-6184ef93123mr96944a12.0.1755007333014; Tue, 12 Aug 2025 07:02:13 -0700 (PDT) MIME-Version: 1.0 References: <20250807103902.2242717-1-lokeshgidra@google.com> In-Reply-To: From: Lokesh Gidra Date: Tue, 12 Aug 2025 07:01:59 -0700 X-Gm-Features: Ac12FXzRyXJqfak0AaNtuxx8F0LqwDc8XieRTyx4WZgakbpJYqJSaaF7hnoQRlc Message-ID: Subject: Re: [PATCH v3] userfaultfd: opportunistic TLB-flush batching for present pages in MOVE To: Peter Xu 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 2626714000D X-Rspam-User: X-Stat-Signature: jm5hdk85wnpejekntqsawpj9cno4gf9e X-Rspamd-Server: rspam09 X-HE-Tag: 1755007334-826426 X-HE-Meta: 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 imMZwzDo LV3el1GxcvoOzsjJ90KoWrzLdNgSZLe6puR5+SPBFUhM8czm0xvC2o9qbm49PfU1LJzwoLdyd8oFrexdzt1FklpzWaY5O231vrMlcpvW3C6PPup2wo6vC6qkwkGavKXFfYchPotxz5yyBCC0aVHpkowxEjRKfy/88q8DNL4K/4nIN4sfyx5MGW78I+Vz3WPp+fyDIVPv9YxuYQXZLjLYGV9ZdnA== 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: List-Subscribe: List-Unsubscribe: On Mon, Aug 11, 2025 at 7:00=E2=80=AFAM Peter Xu wrote: > > On Fri, Aug 08, 2025 at 09:29:58AM -0700, Lokesh Gidra wrote: > > On Thu, Aug 7, 2025 at 12:17=E2=80=AFPM Peter Xu wr= ote: > > > > > > Hi, Lokesh, > > > > > > On Thu, Aug 07, 2025 at 03:39:02AM -0700, Lokesh Gidra wrote: > > > > MOVE ioctl's runtime is dominated by TLB-flush cost, which is requi= red > > > > 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 UF= FD GC, > > > > which uses MOVE ioctl for compaction, we observed that out of the t= otal > > > > 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 ove= r > > > > 70% of move_pages_pte() without any changes to vm_normal_folio(). > > > > > > Do you know why vm_normal_folio() could be expensive? I still see qui= te > > > some other things this path needs to do. > > > > > Let's discuss this in Andrew's reply thread. > > Sorry to get back to this late. Thanks for the link, Andrew! > > > > > > > Furthermore, time spent within move_pages_pte() is only ~20%, which > > > > includes TLB-flush overhead. > > > > > > Indeed this should already prove the optimization, I'm just curious w= hether > > > you've run some benchmark on the GC app to show the real world benefi= t. > > > > > I did! The same benchmark through which I gathered these numbers, when > > run on cuttlefish (qemu android instance on x86_64), the completion > > time of the benchmark went down from ~45mins to ~20mins. The benchmark > > is very GC intensive and the overhead of IPI on vCPUs seems to be > > enormous leading to this drastic improvement. > > > > In another instance, system_server, one of the most critical system > > processes on android, saw over 50% reduction in GC compaction time on > > an arm64 android device. > > Would you mind add some of these numbers into the commit message when you > repost? I can certainly do that in v5. But I already sent v4 addressing all your other feedback. I'll incorporate these numbers as well as any additional changes suggested in v4 in v5. > > Thanks, > > -- > Peter Xu >