[webkit-dev] Disk cache

Benjamin Poulain benjamin at webkit.org
Mon Nov 3 15:03:11 PST 2014

On 11/3/14 11:12 AM, Carlos Garcia Campos wrote:
> El lun, 03-11-2014 a las 00:22 -0800, Benjamin Poulain escribió:
>> On 11/2/14, 1:11 AM, Carlos Garcia Campos wrote:
>>> El sáb, 01-11-2014 a las 20:43 +0200, Antti Koivisto escribió:
>>>> On Sat, Nov 1, 2014 at 10:13 AM, Carlos Garcia Campos
>>>> <carlosgc at webkit.org> wrote:
>>>>           El vie, 31-10-2014 a las 19:02 +0200, Antti Koivisto escribió:
>>>>           > Hello,
>>>>           >
>>>>           >
>>>>           > I'm planning to add an experimental HTTP cache
>>>>           implementation to
>>>>           > WebKit (https://bugs.webkit.org/show_bug.cgi?id=30322).
>>>>           Great news!
>>>>           >  The main motivations are:
>>>>           >
>>>>           >
>>>>           > - Improving performance by bringing the cache closer. For
>>>>           example we
>>>>           > can serialize WebKit response objects directly instead of
>>>>           converting
>>>>           > to/from platform types.
>>>>           > - Making future innovation around caching easier. Closer
>>>>           coordination
>>>>           > between cache and WebKit opens new optimization
>>>>           possibilities.
>>>>           >
>>>>           >
>>>>           > The cache lives in the network process. Most of the code is
>>>>           > cross-platform. The storage backend uses libdispatch IO
>>>>           though it
>>>>           > wouldn't be hard to add a generic posix one too.
>>>>           Why is it limited to the network process? wouldn't it be
>>>>           possible to use
>>>>           it also in the web process when shared secondary process model
>>>>           is used?
>>>> The cache ties to NetworkResourceLoader which lives in the network
>>>> process. In principle it would be possible to integrate with the web
>>>> process side resource loader too. However I don't want to support
>>>> multiple configurations during development.
>>>> It would be good if all WK2 ports would eventually switch to using the
>>>> network process. The current multitude of configurations makes
>>>> networking related code more confusing and less hackable than it needs
>>>> to be.
>>> The GTK+ port supports the network process, but it's only used when
>>> multiple secondary process model is used. Some applications prefer the
>>> single shared secondary process model, and even some of the browser
>>> users change the default process model of epiphany to single web process
>>> because it requires fewer resources. So, we could either integrate the
>>> cache with the web process loader, or use the network process
>>> unconditionally for all process models. I think for many simple
>>> applications a single web process is the most efficient model, though.
>> I believe it would be better to enable the network process for all
>> process models. Maintaining multiple configurations for marginal gains
>> is not sustainable, especially in the network stack.
>> You say a single Web Process is the most efficient model for some
>> applications. What is the impact of always enabling the network process on:
>> -CPU load?
>> -Memory load?
>> -Overall performance?
> I haven't measured, I was thinking mainly on the overhead of the IPC
> traffic required for the network resources.

On iOS, we managed to optimize this until IPC was no longer a major 
performance concern. Our IPC should definitely improve but it is not a 
high priority for performance.

You could argue that iOS runs on very unconventional CPUs but we also 
have some old ARMv7 that are close to conventional CPU and we managed 
reasonable overhead on those too.

In my humble opinion, we should just get hard data and solve the actual 
problems (which I suspect may be memory and not IPC).


>> Once we know where the problems are, we should work together at reducing
>> the impact. I suspect we can get the network process below 5% overhead.
>> Benjamin
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