[whatwg] Low Memory Event

Charles Pritchard chuck at jumis.com
Sat Jan 1 14:04:12 PST 2011

On 1/1/2011 1:43 PM, Glenn Maynard wrote:
> You need to know a lot about the host system to know what "low memory"
> even means.  Does it mean allocations may start failing soon?  Does it
> This definitely seems useful on mobile platforms, where memory is much
> more limited, memory management is much less complex, and being able
> to deal reliably with memory limitations is a much more pressing
> issue.  But on desktop platforms, even native applications written for
> a specific platform run into trouble when they try to respond
> "intelligently" to memory pressure, and the vast majority don't try.
I realize it's an exotic feature.

The separation of Mobile and Desktop seems arbitrary, in terms of specs:
if it's useful on the mobile, why would it not be useful on the desktop?

It's the same concept, a memory warning.
> On Sat, Jan 1, 2011 at 3:39 PM, Charles Pritchard<chuck at jumis.com>  wrote:
>> Here are some example implementations; it's up to the vendor, not the spec.
>> Tabbed browsing implementation:
>> Send a lowmemory event to hidden tabs listening (for lowmemory), that have
>> not been visible for more than 60 seconds.
>> (This is a partial example, as it doesn't detail when the tabs would be
>> checked for visibility. )
> An event like this needs to have a consistent meaning to allow
> applications to respond meaningfully.  If it has varied meanings--or
> if it has attributes to indicate each meaning, but they don't get
> implemented in practice, or are too generic and don't accurately
> describe the situation on each platform and configuration--then
> applications can't respond correctly.
It has a consistent meaning, again, though, we're talking about whether 
it's a semantic meaning or a technical one.

The technical meaning, "we can't allocate memory" isn't something that 
can be used on every platform, per Boris' comments.
The semantic meaning is pretty straightforward: low memory warning.

It's really up to the author to decide what they want to do with a low 
memory warning,
and up to the vendor to decide if they want to send one out.

Anything else seems to be impractical.

> For example, responding to being an idle tab by releasing resources is
> the wrong thing to do if there's plenty of memory available.  I have 8
> GB of memory and Firefox rarely uses more than 512 MB.  Don't make me
I stated, in the example, that it would need more logic to function 

It was just a simple example to demonstrate that memory can be released
without OS support, and that applications could use that information.

> I'm not saying this is impossible, but memory management is
> exceptionally complex, varies wildly across platforms, varies wildly
> depending on how much memory and swap a system has, and on the
> behavior of other applications on the system.  I'd be concerned about
> a generic, loosely-defined "lowmemory" event with entirely unrelated
> meanings encouraging developers to respond to it in ways that only
> happen to make sense on the platform they're testing on.

They all have the same related meaning: get rid of unnecessary buffers, 
serialize and save to disk, if appropriate.

If I had a lowmemory event on the desktop, I'd run it through the exact 
same logic I would on mobile.

Without the generic lowmemory, we're just going to go on without the 
event (except in extensions),
with visibility/focus the only tool to test with.


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