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

[Barry Song]

On Tue, May 19, 2026 at 12:17 AM Matthew Wilcox <willy at infradead.org> wrote:
>
> On Mon, May 18, 2026 at 07:25:54PM +0800, Barry Song wrote:
> > We have clearly observed that the `fork()` operations of many
> > popular Android apps, such as iQiyi, Baidu Tieba, and 10086,
> > end up waiting on page-fault (PF) I/O when the VMA lock is
> > held during I/O operations. This has already become a
> > practical issue. I also believe this can lead to chained
> > waiting, since the global `mmap_lock` blocks all threads that
> > need to acquire it.
>
> It's always been a terrible idea to call fork() from a multithreaded
> application.  For example, this question:
>
> https://stackoverflow.com/questions/53601200/calling-fork-on-a-multithreaded-process
>
> or this lwn thread: https://lwn.net/Articles/674660/
>
> Do we have any insight into why these applications are doing this
> horrible thing?

I swear I read the two links you shared. But the reality
is that as long as people use the Android framework,
even the simplest "Hello World" app already runs with
10+ threads :-)


main
RenderThread
ReferenceQueueDaemon
FinalizerDaemon
FinalizerWatchdogDaemon
HeapTaskDaemon
Binder:1234_1
Binder:1234_2
Signal Catcher
JDWP
...

Best Regards
Barry