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From: Yury Norov <yury.norov@gmail.com>
To: Barry Song <song.bao.hua@hisilicon.com>
Cc: gregkh@linuxfoundation.org, akpm@linux-foundation.org,
	andriy.shevchenko@linux.intel.com, linux-kernel@vger.kernel.org,
	dave.hansen@intel.com, linux@rasmusvillemoes.dk,
	rafael@kernel.org, rdunlap@infradead.org, agordeev@linux.ibm.com,
	sbrivio@redhat.com, jianpeng.ma@intel.com,
	valentin.schneider@arm.com, peterz@infradead.org,
	bristot@redhat.com, guodong.xu@linaro.org,
	tangchengchang@huawei.com, prime.zeng@hisilicon.com,
	yangyicong@huawei.com, tim.c.chen@linux.intel.com,
	linuxarm@huawei.com, Tian Tao <tiantao6@hisilicon.com>
Subject: Re: [PATCH v7 1/4] cpumask: introduce cpumap_print_to_buf to support large bitmask and list
Date: Thu, 15 Jul 2021 08:28:38 -0700	[thread overview]
Message-ID: <YPBUJmqk4akuX8cv@yury-ThinkPad> (raw)
In-Reply-To: <20210715115856.11304-2-song.bao.hua@hisilicon.com>

On Thu, Jul 15, 2021 at 11:58:53PM +1200, Barry Song wrote:
> (10.1.198.147)
> X-CFilter-Loop: Reflected
> Status: O
> Content-Length: 10263
> Lines: 252
> 
> From: Tian Tao <tiantao6@hisilicon.com>

[...]

> +int bitmap_print_to_buf(bool list, char *buf, const unsigned long *maskp,
> +		int nmaskbits, loff_t off, size_t count)
> +{
> +	const char *fmt = list ? "%*pbl\n" : "%*pb\n";
> +	ssize_t size;
> +	void *data;
> +
> +	data = kasprintf(GFP_KERNEL, fmt, nmaskbits, maskp);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	size = memory_read_from_buffer(buf, count, &off, data, strlen(data) + 1);
> +	kfree(data);
> +
> +	return size;
> +}
> +EXPORT_SYMBOL(bitmap_print_to_buf);

In discussion to v4 of this series I've pointed out inefficiency of
this approach. Now it's v7, but the problem is still there.

1. You make user of your API guess aboout proper @count without any
   hint. This is worse than how it works now with pure vsnprintf().
2. For big bitmaps and small @count, your code will make enormous
   amount of unneeded work. For example, if the full length of string
   representation of bitmap is 1M, and length of the output buffer is
   1k, one will have to call bitmap_print_to_buf() 1000 times.  With
   current design it assumes that you allocate the full amount of memory
   1000 times, free it 1000 times and print huge bitmap 1000 times to
   just return small part of it.

NAK for this, and please stop submitting wrong approach again and
again.

  reply	other threads:[~2021-07-15 15:28 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-15 11:58 [PATCH v7 0/4] use bin_attribute to break the size limitation of cpumap ABI Barry Song
2021-07-15 11:58 ` [PATCH v7 1/4] cpumask: introduce cpumap_print_to_buf to support large bitmask and list Barry Song
2021-07-15 15:28   ` Yury Norov [this message]
2021-07-15 21:08     ` Song Bao Hua (Barry Song)
2021-07-16  0:57     ` Song Bao Hua (Barry Song)
2021-07-15 11:58 ` [PATCH v7 2/4] topology: use bin_attribute to break the size limitation of cpumap ABI Barry Song
2021-07-16  8:49   ` Song Bao Hua (Barry Song)
2021-07-16 20:04     ` Yury Norov
2021-07-17  0:16       ` Song Bao Hua (Barry Song)
2021-07-17  1:12         ` Yury Norov
2021-07-19  9:07           ` andriy.shevchenko
2021-07-19 11:10             ` Song Bao Hua (Barry Song)
2021-07-19 17:10               ` Yury Norov
2021-07-21  9:30                 ` Song Bao Hua (Barry Song)
2021-07-15 11:58 ` [PATCH v7 3/4] drivers/base/node.c: " Barry Song
2021-07-15 11:58 ` [PATCH v7 4/4] lib: test_bitmap: add bitmap_print_to_buf test cases Barry Song
2021-07-15 12:09   ` Andy Shevchenko
2021-07-15 20:47     ` Yury Norov
2021-07-15 21:32       ` Andy Shevchenko
2021-07-15 23:23         ` Yury Norov
2021-07-16  0:41           ` Song Bao Hua (Barry Song)
2021-07-21 11:40           ` Greg Kroah-Hartman
2021-07-22 17:09             ` Yury Norov
2021-07-22 17:47               ` Greg Kroah-Hartman
2021-07-22 18:27                 ` Yury Norov
2021-07-22 18:36                   ` Andy Shevchenko
2021-07-22 18:45                   ` Greg Kroah-Hartman
2021-07-28  9:08                     ` Song Bao Hua (Barry Song)
2021-07-28  9:24                       ` Andy Shevchenko
2021-07-15 15:36   ` Yury Norov
2021-07-28 13:41 ` [PATCH v7 0/4] use bin_attribute to break the size limitation of cpumap ABI Greg KH
2021-07-28 14:53   ` Yury Norov
2021-07-28 15:25     ` Greg KH
2021-07-28 18:58 ` [PATCH] bitmap: extend comment to bitmap_print_to_buf Yury Norov
2021-07-29  6:04   ` Song Bao Hua (Barry Song)

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