linux-stable/include/linux/task_io_accounting.h

/*
 * task_io_accounting: a structure which is used for recording a single task's
 * IO statistics.
 *
 * Don't include this header file directly - it is designed to be dragged in via
 * sched.h.
 *
 * Blame akpm@osdl.org for all this.
 */

#ifdef CONFIG_TASK_IO_ACCOUNTING
struct 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;
};
#else
struct task_io_accounting {
};
#endif
[PATCH] io-accounting: core statistics The present per-task IO accounting isn't very useful. It simply counts the number of bytes passed into read() and write(). So if a process reads 1MB from an already-cached file, it is accused of having performed 1MB of I/O, which is wrong. (David Wright had some comments on the applicability of the present logical IO accounting: For billing purposes it is useless but for workload analysis it is very useful read_bytes/read_calls average read request size write_bytes/write_calls average write request size read_bytes/read_blocks ie logical/physical can indicate hit rate or thrashing write_bytes/write_blocks ie logical/physical guess since pdflush writes can be missed I often look for logical larger than physical to see filesystem cache problems. And the bytes/cpusec can help find applications that are dominating the cache and causing slow interactive response from page cache contention. I want to find the IO intensive applications and make sure they are doing efficient IO. Thus the acctcms(sysV) or csacms command would give the high IO commands). This patchset adds new accounting which tries to be more accurate. We account for three things: reads: attempt to count the number of bytes which this process really did cause to be fetched from the storage layer. Done at the submit_bio() level, so it is accurate for block-backed filesystems. I also attempt to wire up NFS and CIFS. writes: attempt to count the number of bytes which this process caused to be sent to the storage layer. This is done at page-dirtying time. The big inaccuracy here is truncate. If a process writes 1MB to a file and then deletes the file, it will in fact perform no writeout. But it will have been accounted as having caused 1MB of write. So... cancelled_writes: account the number of bytes which this process caused to not happen, by truncating pagecache. We _could_ just subtract this from the process's `write' accounting. But that means that some processes would be reported to have done negative amounts of write IO, which is silly. So we just report the raw number and punt this decision up to userspace. Now, we _could_ account for writes at the physical I/O level. But - This would require that we track memory-dirtying tasks at the per-page level (would require a new pointer in struct page). - It would mean that IO statistics for a process are usually only available long after that process has exitted. Which means that we probably cannot communicate this info via taskstats. This patch: Wire up the kernel-private data structures and the accessor functions to manipulate them. Cc: Jay Lan <jlan@sgi.com> Cc: Shailabh Nagar <nagar@watson.ibm.com> Cc: Balbir Singh <balbir@in.ibm.com> Cc: Chris Sturtivant <csturtiv@sgi.com> Cc: Tony Ernst <tee@sgi.com> Cc: Guillaume Thouvenin <guillaume.thouvenin@bull.net> Cc: David Wright <daw@sgi.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org> 2006-12-10 10:19:19 +00:00			`/*`
			`* task_io_accounting: a structure which is used for recording a single task's`
			`* IO statistics.`
			`*`
			`* Don't include this header file directly - it is designed to be dragged in via`
			`* sched.h.`
			`*`
			`* Blame akpm@osdl.org for all this.`
			`*/`

			`#ifdef CONFIG_TASK_IO_ACCOUNTING`
			`struct 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;`
			`};`
			`#else`
			`struct task_io_accounting {`
			`};`
			`#endif`