Re: [PATCH v2 0/5] mm: reduce mmap_lock contention and improve page fault performance

[David Hildenbrand (Arm)]

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