linux-kernel - Re: [PATCH] fs/buffer.c: Add checking buffer head stat before clear

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Message-Id: <20210205154548.49dd62b161b794b9f29026f1@linux-foundation.org>
Date:   Fri, 5 Feb 2021 15:45:48 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Shaokun Zhang <zhangshaokun@...ilicon.com>
Cc:     <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Yang Guo <guoyang2@...wei.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH] fs/buffer.c: Add checking buffer head stat before clear

On Wed, 3 Feb 2021 14:14:50 +0800 Shaokun Zhang <zhangshaokun@...ilicon.com> wrote:

> From: Yang Guo <guoyang2@...wei.com>
> 
> clear_buffer_new() is used to clear buffer new stat. When PAGE_SIZE
> is 64K, most buffer heads in the list are not needed to clear.
> clear_buffer_new() has an enpensive atomic modification operation,
> Let's add checking buffer head before clear it as __block_write_begin_int
> does which is good for performance.

Did this produce any measurable improvement?

Perhaps we should give clear_buffer_x() the same optimization as
set_buffer_x()?


static __always_inline void set_buffer_##name(struct buffer_head *bh)	\
{									\
	if (!test_bit(BH_##bit, &(bh)->b_state))			\
		set_bit(BH_##bit, &(bh)->b_state);			\
}									\
static __always_inline void clear_buffer_##name(struct buffer_head *bh)	\
{									\
	clear_bit(BH_##bit, &(bh)->b_state);				\
}									\