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Date:   Fri, 30 Aug 2019 08:39:43 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Peikan Tsai <peikantsai@gmail.com>
Cc:     Christian Brauner <christian.brauner@ubuntu.com>,
        devel@driverdev.osuosl.org, tkjos@android.com,
        linux-kernel@vger.kernel.org, arve@android.com,
        Joel Fernandes <joel@joelfernandes.org>, maco@android.com
Subject: Re: [PATCH] binder: Use kmem_cache for binder_thread
Message-ID: <20190830063943.GH15257@kroah.com>
References: <20190829054953.GA18328@mark-All-Series>
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 <20190829152721.ttsyfwaeygmwmcu7@wittgenstein>
 <20190829185901.GA4680@mark-All-Series>
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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???