[Webkit-unassigned] [Bug 159346] [GLib] Use a GSource instead of a thread to poll memory pressure eventFD in linux implementation

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=159346

Antonio Gomes <tonikitoo at webkit.org> changed:

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--- Comment #9 from Antonio Gomes <tonikitoo at webkit.org> ---
Comment on attachment 283522
  --> https://bugs.webkit.org/attachment.cgi?id=283522
Updated patch

View in context: https://bugs.webkit.org/attachment.cgi?id=283522&action=review

r=me.

I think I can't make use of it yet out of the box on my Linux box, because applications (including webkit based browsers) can not read '/sys/fs/cgroup/memory/memory.pressure_level'.

$ ls -ls /sys/fs/cgroup/memory/
(..)
0 --w--w--w-. 1 root root 0 Jul  5 11:37 cgroup.event_control
(..)
0 ----------. 1 root root 0 Jul  5 11:37 memory.pressure_level
(..)

I have to manually change the permissions.

>>> Source/WebCore/platform/linux/MemoryPressureHandlerLinux.cpp:230
>>> +    m_eventFDPoller = std::make_unique<EventFDPoller>(m_eventFD.value(), [this] {
>> 
>> So my understand is that m_eventFDPoller is an alternative memory pressure source that works independent from the existing 'cgroup' solution, right?
>> 
>> However, it gets initialized after the cgroup initialization stuff (lines 209 and 215). So, if cgroup fails to initialize - which happens in most cases - then ::install bails out earlier (lines 218 and 225) and line 230 is not executed.
>> 
>> Should line 230 be our first option, and cgroup the second?
> 
> No, cgroups work with an evenfd. You create an eventfd and pass the file descriptor to the cgroup event control, by writing a line to /sys/fs/cgroup/memory/cgroup.event_control. The kernel uses the passed fd to notify about critical memory situations. In bug #155255 I also use an eventfd because it's light an efficient and we can reuse most of the cgroups code.

Ok.

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