Re: [PATCH] binder: Use kmem_cache for binder_thread

Peikan Tsai
2019-08-29T18:59:08Z

On Thu, Aug 29, 2019 at 05:27:22PM +0200, Christian Brauner wrote:
> On Thu, Aug 29, 2019 at 09:53:59AM -0400, Joel Fernandes wrote:
> > On Thu, Aug 29, 2019 at 08:42:29AM +0200, Greg KH wrote:
> > > On Thu, Aug 29, 2019 at 01:49:53PM +0800, Peikan Tsai wrote:
> > [snip]
> > > > The allocated size for each binder_thread is 512 bytes by kzalloc.
> > > > Because the size of binder_thread is fixed and it's only 304 bytes.
> > > > It will save 208 bytes per binder_thread when use create a kmem_cache
> > > > for the binder_thread.
> > >
> > > Are you _sure_ it really will save that much memory? You want to do
> > > allocations based on a nice alignment for lots of good reasons,
> > > especially for something that needs quick accesses.
> >
> > Alignment can be done for slab allocations, kmem_cache_create() takes an
> > align argument. I am not sure what the default alignment of objects is
> > though (probably no default alignment). What is an optimal alignment in your
> > view?
>
> Probably SLAB_HWCACHE_ALIGN would make most sense.
>

Agree. Thanks for yours comments and suggestions.
I'll put SLAB_HWCACHE_ALIGN it in patch v2.

> >
> > > Did you test your change on a system that relies on binder and find any
> > > speed improvement or decrease, and any actual memory savings?
> > >
> > > If so, can you post your results?
> >
> > That's certainly worth it and I thought of asking for the same, but spoke too
> > soon!
>
> Yeah, it'd be interesting to see what difference this actually makes.
>
> Christian

I tested this change on an Android device(arm) with AOSP kernel 4.19 and
observed
memory usage of binder_thread. But I didn't do binder benchmark yet.

On my platform the memory usage of binder_thread reduce about 90 KB as
the
following result.
nr obj obj size total
before: 624 512 319488 bytes
after: 728 312 227136 bytes