linux-kernel - Re: [PATCH] binder: Use kmem_cache for binder

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Date:   Thu, 29 Aug 2019 17:27:22 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Peikan Tsai <peikantsai@...il.com>, arve@...roid.com,
        tkjos@...roid.com, maco@...roid.com, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] binder: Use kmem_cache for binder_thread

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.

> 
> > 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