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b=FklgZfZvf9emq2gmny2eGq6EMuPFgTPg3jmwAxmLaYfdeYYOx9o/LUsxGSyhC90Aj wyT19RvXdWlMCbyU9x5qRfWKwzHtDUwLyiTaRdHPzlhCnqASxByUiH+reBxZa6dm6/ 2eUrKJ7Sl3Ard2QCWFs5RMYz0cEIAQCf+F3cTsedtE8mzwpzHancQo4aEImHF0L8cr Fy0cEII7dznV9is/6QM/nYIXsQ76KUnc8J3lz0n9fEPXD9BgbtOHKKHco2unHFN5KT hMyDhDgPqCuk0aLgK7toBqI2XUvKRYcOcAAOK274SYOnvXU30gUDeEG5XgOjyI10Dd 19K+31feZDQsg== Message-ID: Date: Tue, 23 Jun 2026 10:02:40 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/5] mm: reduce mmap_lock contention and improve page fault performance To: Hongru Zhang Cc: akpm@linux-foundation.org, baohua@kernel.org, bhe@redhat.com, chentao@kylinos.cn, chrisl@kernel.org, jack@suse.cz, kasong@tencent.com, kunwu.chan@gmail.com, liam@infradead.org, lianux.mm@gmail.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, liyangouwen1@oppo.com, ljs@kernel.org, loongarch@lists.linux.dev, mhocko@suse.com, nphamcs@gmail.com, nzzhao@126.com, pfalcato@suse.de, rppt@kernel.org, shikemeng@huaweicloud.com, surenb@google.com, vbabka@kernel.org, wanglian@kylinos.cn, willy@infradead.org, youngjun.park@lge.com References: <3be9475b-0e8a-4df8-a130-4262f993973d@kernel.org> <20260623075805.466317-1-zhanghongru@xiaomi.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D6A6840006 X-Stat-Signature: b8uim78zuwusixwmnubxfywfozigmcpn X-HE-Tag: 1782201772-740556 X-HE-Meta: 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 z1nx8y7V RntAudqfg6+awSE0oa2p9JqQkYljcrHqdnnXqvgHX0+nuJJ4i0Vn/9mX+OCzoeKZJ6M2ITaEt9muAMBy8btZnVjW7ibgy3HXlegmd/u8xv8h6wcK0hbedk/qrEot2MBuQRrmOduoltNo9agBchq5mraedCoZ+TEB8tTjJqHiEx0pd18oWCxrKUWe/ZXLCojevUI0T6HtyKNjuWI0LcTPUe24tpo/JZ6BrXcSfjnvxnXDefjwJk64zCcA4EISB1KXcb9Xq4a2a6oAojQSp4Ehy7XCEvitgwyPQUVT/mycvGUWg2XZhSZczt57baUYP/mh+7Lvb/4MATOxJteRsLzJGmnzZq6jDp7OrnBoz59cR765MbC5h4QklYKAqTVIv32qZVjAEVoEOIGiO6rsJDI5eRX0I6A== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/23/26 09:58, Hongru Zhang wrote: >> On 5/20/26 23:15, Matthew Wilcox wrote: >>> >>> all of the applications i run are either single threaded or don't fork. >>> what multithreaded applications call fork? >> >> Traditionally the problem was random libraries using fork+execve to launch other >> programs ... instead of using alternatives like posix_spwan (some use cases >> require more work done before execve and cannot yet switch to that). I'd hope >> that that is less of a problem on Android. >> >> I assume Android zygote might be multi threaded? Maybe sshd as well? Systemd? >> But I'd be surprised if there are really performance implications. >> >> Not sure about webbroswers .... I think most of them switched to fork servers, >> where I would assume fork servers would be single-threaded. >> >> So, yeah, getting a clear understanding how this ends up being a problem on >> Android would be great. > > Barry asked me to share observations on fork() usage across Android > applications. > > I wrote a BPF-based tracing tool (kprobe on copy_process, checking > CLONE_VM to distinguish process creation from thread creation) and ran > it against the top 200 Android applications in the China market during > normal usage scenarios. > > Results: > - 82 out of 200 apps (41%) call fork() during normal operation Crazy. Thanks for these numbers. > - Among these, some call fork() from multiple threads > > These are not zygote forks — they are fork() calls initiated by app > threads at runtime. Examples by category: > > Browsers: com.quark.browser, com.UCMobile, com.xunlei.browser > Shopping: com.taobao.taobao, com.tmall.wireless, com.achievo.vipshop > Video: com.youku.phone, com.qiyi.video, com.hunantv.imgo.activity > Social/IM: com.alibaba.android.rimet, com.ss.android.lark > News: com.ss.android.article.news, com.ss.android.article.lite > Navigation: com.autonavi.minimap, com.sdu.didi.psnger > Finance: com.eg.android.AlipayGphone, com.chinamworld.main I know that especially browser usually use fork servers: a tiny (single-threaded) process just to create new child processes. Any information regarding the apps above that use fork() on small vs. large processes? > > This confirms that fork() is widely used in real-world multi-threaded > Android applications. Above you write "some call fork() from multiple threads". Any further information on that? -- Cheers, David