linux-kernel - Re: [PATCH v2 2/2] Enhance read_block of page

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Date:	Fri, 11 Jan 2013 17:01:29 +0100
From:	Michal Nazarewicz <mina86@...a86.com>
To:	Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Minchan Kim <minchan@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Andy Whitcroft <apw@...dowen.org>,
	Alexander Nyberg <alexn@....su.se>,
	Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v2 2/2] Enhance read_block of page_owner.c

It occurred to me -- and I know it will sound like a heresy -- that
maybe providing an overly long example in C is not the best option here.
Why not page_owner.py with the following content instead (not tested):


#!/usr/bin/python
import collections
import sys

counts = collections.defaultdict(int)

txt = ''
for line in sys.stdin:
    if line == '\n':
        counts[txt] += 1
        txt = ''
    else:
        txt += line
counts[txt] += 1

for txt, num in sorted(counts.items(), txt=lambda x: x[1]):
    if len(txt) > 1:
        print '%d times:\n%s' % num, txt


And it's so “long” only because I chose not to read the whole file at
once as in:

    
counts = collections.defaultdict(int)
for txt in sys.stdin.read().split('\n\n'):
    counts[txt] += 1


On Fri, Jan 11 2013, Minchan Kim wrote:
> The read_block reads char one by one until meeting two newline.
> It's not good for the performance and current code isn't good shape
> for readability.
>
> This patch enhances speed and clean up.
>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Andy Whitcroft <apw@...dowen.org>
> Cc: Alexander Nyberg <alexn@....su.se>
> Cc: Randy Dunlap <rdunlap@...radead.org>
> Signed-off-by: Michal Nazarewicz <mina86@...a86.com>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
>  Documentation/page_owner.c |   34 +++++++++++++---------------------
>  1 file changed, 13 insertions(+), 21 deletions(-)
>
> diff --git a/Documentation/page_owner.c b/Documentation/page_owner.c
> index 43dde96..96bf481 100644
> --- a/Documentation/page_owner.c
> +++ b/Documentation/page_owner.c
> @@ -28,26 +28,17 @@ static int max_size;
>  
>  struct block_list *block_head;
>  
> -int read_block(char *buf, FILE *fin)
> +int read_block(char *buf, int buf_size, FILE *fin)
>  {
> -	int ret = 0;
> -	int hit = 0;
> -	int val;
> -	char *curr = buf;
> -
> -	for (;;) {
> -		val = getc(fin);
> -		if (val == EOF) return -1;
> -		*curr = val;
> -		ret++;
> -		if (*curr == '\n' && hit == 1)
> -			return ret - 1;
> -		else if (*curr == '\n')
> -			hit = 1;
> -		else
> -			hit = 0;
> -		curr++;
> +	char *curr = buf, *const buf_end = buf + buf_size;
> +
> +	while (buf_end - curr > 1 && fgets(curr, buf_end - curr, fin)) {
> +		if (*curr == '\n') /* empty line */
> +			return curr - buf;
> +		curr += strlen(curr);
>  	}
> +
> +	return -1; /* EOF or no space left in buf. */
>  }
>  
>  static int compare_txt(struct block_list *l1, struct block_list *l2)
> @@ -84,10 +75,12 @@ static void add_list(char *buf, int len)
>  	}
>  }
>  
> +#define BUF_SIZE	1024
> +
>  int main(int argc, char **argv)
>  {
>  	FILE *fin, *fout;
> -	char buf[1024];
> +	char buf[BUF_SIZE];
>  	int ret, i, count;
>  	struct block_list *list2;
>  	struct stat st;
> @@ -106,11 +99,10 @@ int main(int argc, char **argv)
>  	list = malloc(max_size * sizeof(*list));
>  
>  	for(;;) {
> -		ret = read_block(buf, fin);
> +		ret = read_block(buf, BUF_SIZE, fin);
>  		if (ret < 0)
>  			break;
>  
> -		buf[ret] = '\0';
>  		add_list(buf, ret);
>  	}
>  
> -- 
> 1.7.9.5
>

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +----<email/xmpp: mpn@...gle.com>--------------ooO--(_)--Ooo--

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