[Webkit-unassigned] [Bug 155255] MemoryPressureHandler doesn't work if cgroups aren't present in Linux

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=155255

--- Comment #26 from Antonio Gomes <tonikitoo at webkit.org> ---
(In reply to comment #25)
> Comment on attachment 273833 [details]
> Patch
> 
> I think this patch needs to address clopez's feedback:
> 
> """Regarding the concerns about that the wakeups could affect the battery
> life I propose that we only enable this fallback memory pressure handler
> when the system is not running on battery.
> 
> We can reliably detect this by inspecting some values on /sys. For example,
> we can borrow either the systemd implementation to detect this
> <https://github.com/systemd/systemd/blob/master/src/basic/util.c#L498> or
> the e2fsprogs one
> <http://git.kernel.org/cgit/fs/ext2/e2fsprogs.git/tree/e2fsck/unix.c#n284>
> (yes, fsck avoids running automatically if it detects you are on battery)
> 
> 
> And I don't think we should hide this feature behind an obscure environment
> variable than other than we developers and power users will know about, but
> make it run by default when the cgroup based memory pressure handler fails
> and when the system is not running on battery."""

For the record, on ChromeOS, the kernel provides a file (available for reading if system is under low mem conditions):

// This is the file that will exist if low memory notification is available
// on the device.  Whenever it becomes readable, it signals a low memory
// condition.
const char kLowMemFile[] = "/dev/chromeos-low-mem";

No parsing needed of its content, just verifying its presence is enough.
The check happens every 1s, and I believe it would not be as expensive as actually reading and parsing /proc/meminfo every 1s.
If Linux would have something like this by default, it would do it, as far as I can tell.

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