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Cc: linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org
From: Kyle Moffett <mrmacman_g4@mac.com>
Subject: Re: [ patch 1/7] drivers/serial/jsm: new serial device driver
Date: Sun, 27 Feb 2005 19:05:24 -0500
To: Wen Xiong <wendyx@us.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
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On Feb 27, 2005, at 18:38, Wen Xiong wrote:
> +/*
> + * jsm_init_globals()
> + *
> + * This is where we initialize the globals from the static insmod
> + * configuration variables.  These are declared near the head of
> + * this file.
> + */
> +static void jsm_init_globals(void)
> +{
> +	int i = 0;
> +
> +	jsm_rawreadok		= rawreadok;
> +	jsm_trcbuf_size		= trcbuf_size;
> +	jsm_debug		= debug;
> +
> +	for (i = 0; i < MAXBOARDS; i++) {
> +		jsm_Board[i] = NULL;
> +		jsm_board_slot[i] = (char *)kmalloc(20, GFP_KERNEL);
> +		memset(jsm_board_slot[i], 0, 20);
> +	}

Instead of several 20-byte kmallocs, you could help reduce memory
usage and fragmentation with something like this:

static void *jsm_board_slot_mem;

jsm_board_slot_mem = kmalloc(20*MAXBOARDS, GFP_KERNEL);
memset(jsm_board_slot_mem, 0, 20*MAXBOARDS)
for (i = 0; i < MAXBOARDS; i++) {
	jsm_Board[i] = NULL;
	jsm_board_slot[i] = &jsm_board_slot_mem[20*i];
}

Then free like this:
kfree(jsm_board_slot_mem);

On the other hand, it might be nice to have all these structures
dynamically allocated, so that the no-boards case only uses the 8 or
16 bytes of RAM required for a struct list_head.  In that case you
could clump the other board info into a single struct instead of
multiple independent static arrays.  Something like this might work:

struct jsm_board_instance {
	struct list_head board_list;
	struct board_t board;
	char slot[20];
	[...etc...]
};
static struct list_head jsm_board_list = LIST_HEAD_INIT(jsm_board_list);
static spinlock_t jsm_board_list_lock = SPIN_LOCK_UNLOCKED;

Then when doing hardware add/remove, take the lock and do the list
manipulation, then unlock.

Cheers,
Kyle Moffett

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