Re: [PATCH] binder: Use kmem_cache for binder_thread

[Peikan Tsai <peikantsai@gmail.com>]

On Fri, Aug 30, 2019 at 08:39:43AM +0200, Greg KH wrote:
> On Fri, Aug 30, 2019 at 02:59:01AM +0800, Peikan Tsai wrote:
> > 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
> 
> You have more objects???
> 

Sorry, it's total objects which include some inactive objects ...
And because I tested it on an Android platform so there may be some noise.

So I try 'adb stop' and 'echo 3 > /proc/sys/vm/drop_caches' before starting
test to reduce the noise, and the result are as following.

                    objs
kzalloc              220  (kmalloc-512 alloc by binder_get_thread)

             active_objs  total objs   objperslab  slabdata
kmem_cache           194         403           13        31

Seems there are more objects when use kmemcache for binder_thread...
But as I understand it, those inactive objects can be free by kmemcahe shrink?

Also, I tested the throughput by using performace test of Android VTS.

size(bytes)	kzalloc(byte/ns)	kmemcache(byte/ns)
4		0.17			0.17
8		0.33			0.32
16		0.66			0.66
32		1.36			1.42
64		2.66			2.61
128		5.4			5.26
256		10.29			10.77
512		21.51			21.36
1k		41			40.26
2k		82.12			80.28
4k		149.24			146.95
8k		262.34			256
16k		417.96			422.2
32k		596.66			590.23
64k		600.84			601.25