Re: [PATCH] binder: Use kmem_cache for binder_thread

From: joel@joelfernandes.org
To: Peikan Tsai <peikantsai@gmail.com>,
	Christian Brauner <christian.brauner@ubuntu.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
	arve@android.com, tkjos@android.com, maco@android.com,
	devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] binder: Use kmem_cache for binder_thread
Date: Thu, 29 Aug 2019 15:30:38 -0400	[thread overview]
Message-ID: <009FE4FC-E1C2-43A4-AE75-A1FFE9A57356@joelfernandes.org> (raw)
In-Reply-To: <20190829185901.GA4680@mark-All-Series>

On August 29, 2019 2:59:01 PM EDT, Peikan Tsai <peikantsai@gmail.com> 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

And add this to the changelog as well. Curious- why is nrobj higher with the patch?

Please don't use my reviewed-by tag yet and I will review the new patch and provide tag separately.

Thank you.

-- 
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