linux-kernel - Re: [PATCH 1/1] task IO accounting: improve code readability

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Date:	Sun, 27 Jul 2008 23:53:44 +0200
From:	Andrea Righi <righiandr@...rs.sourceforge.net>
To:	Oleg Nesterov <oleg@...sign.ru>
CC:	Andrea Righi <righi.andrea@...il.com>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	balbir@...ux.vnet.ibm.com, matt@...ehost.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] task IO accounting: improve code readability

Oleg Nesterov wrote:
> On 07/27, Andrea Righi wrote:
>> Put all i/o statistics in struct proc_io_accounting and use inline functions to
>> initialize and increment statistics, removing a lot of single variable
>> assignments.
> 
> Imho, the change like this is obviously good, but can't we simplify
> this a little bit? Just make
> 
> 	struct task_io_accounting
> 	{
> 	#ifdef CONFIG_TASK_XACCT
> 		/* bytes read */
> 		u64 rchar;
> 		/*  bytes written */
> 		u64 wchar;
> 		/* # of read syscalls */
> 		u64 syscr;
> 		/* # of write syscalls */
> 		u64 syscw;
> 	#endif /* CONFIG_TASK_XACCT */
> 
> 	#ifdef CONFIG_TASK_IO_ACCOUNTING
> 		/*
> 		 * The number of bytes which this task has caused to be read from
> 		 * storage.
> 		 */
> 		u64 read_bytes;
> 
> 		/*
> 		 * The number of bytes which this task has caused, or shall cause to be
> 		 * written to disk.
> 		 */
> 		u64 write_bytes;
> 
> 		/*
> 		 * A task can cause "negative" IO too.  If this task truncates some
> 		 * dirty pagecache, some IO which another task has been accounted for
> 		 * (in its write_bytes) will not be happening.  We _could_ just
> 		 * subtract that from the truncating task's write_bytes, but there is
> 		 * information loss in doing that.
> 		 */
> 		u64 cancelled_write_bytes;
> 	#endif
> 	};
> 
> This should make the patch much smaller with the same effect, no?
> 
> Oleg.
> 

Sounds good to me. This also makes sense because it merges *all* the i/o
statistics in "struct task_io_accounting", that is a reasonable thing
IMHO. A patch on-top-of the previous one will follow.

-Andrea
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