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

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Date:   Thu, 29 Aug 2019 09:43:29 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Peikan Tsai <peikantsai@...il.com>
Cc:     gregkh@...uxfoundation.org, arve@...roid.com, tkjos@...roid.com,
        maco@...roid.com, christian@...uner.io, 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 01:49:53PM +0800, Peikan Tsai wrote:
> Hi,
> 
> 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.

Awesome change and observation!!!

Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>

(Another thought: how did you discover this? Are you using some tools to look
into slab fragmentation?).

thanks,

 - Joel

> Signed-off-by: Peikan Tsai <peikantsai@...il.com>
> ---
>  drivers/android/binder.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index dc1c83eafc22..043e0ebd0fe7 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -87,6 +87,8 @@ static struct dentry *binder_debugfs_dir_entry_root;
>  static struct dentry *binder_debugfs_dir_entry_proc;
>  static atomic_t binder_last_id;
> 
> +static struct kmem_cache *binder_thread_cachep;
> +
>  static int proc_show(struct seq_file *m, void *unused);
>  DEFINE_SHOW_ATTRIBUTE(proc);
> 
> @@ -4696,14 +4698,15 @@ static struct binder_thread *binder_get_thread(struct binder_proc *proc)
>  	thread = binder_get_thread_ilocked(proc, NULL);
>  	binder_inner_proc_unlock(proc);
>  	if (!thread) {
> -		new_thread = kzalloc(sizeof(*thread), GFP_KERNEL);
> +		new_thread = kmem_cache_zalloc(binder_thread_cachep,
> +					       GFP_KERNEL);
>  		if (new_thread == NULL)
>  			return NULL;
>  		binder_inner_proc_lock(proc);
>  		thread = binder_get_thread_ilocked(proc, new_thread);
>  		binder_inner_proc_unlock(proc);
>  		if (thread != new_thread)
> -			kfree(new_thread);
> +			kmem_cache_free(binder_thread_cachep, new_thread);
>  	}
>  	return thread;
>  }
> @@ -4723,7 +4726,7 @@ static void binder_free_thread(struct binder_thread *thread)
>  	BUG_ON(!list_empty(&thread->todo));
>  	binder_stats_deleted(BINDER_STAT_THREAD);
>  	binder_proc_dec_tmpref(thread->proc);
> -	kfree(thread);
> +	kmem_cache_free(binder_thread_cachep, thread);
>  }
> 
>  static int binder_thread_release(struct binder_proc *proc,
> @@ -6095,6 +6098,12 @@ static int __init binder_init(void)
>  	if (ret)
>  		return ret;
> 
> +	binder_thread_cachep = kmem_cache_create("binder_thread",
> +						 sizeof(struct binder_thread),
> +						 0, 0, NULL);
> +	if (!binder_thread_cachep)
> +		return -ENOMEM;
> +
>  	atomic_set(&binder_transaction_log.cur, ~0U);
>  	atomic_set(&binder_transaction_log_failed.cur, ~0U);
> 
> @@ -6167,6 +6176,7 @@ static int __init binder_init(void)
> 
>  err_alloc_device_names_failed:
>  	debugfs_remove_recursive(binder_debugfs_dir_entry_root);
> +	kmem_cache_destroy(binder_thread_cachep);
> 
>  	return ret;
>  }
> --
> 2.17.1
>