[PATCH] taskstats: use nla_reserve() for reply assembling
[PATCH] taskstats: use nla_reserve() for reply assembling

Currently taskstats_user_cmd()/taskstats_exit() do:

	1) allocate stats
	2) fill stats
	3) make a temporary copy on stack (236 bytes)
	4) copy that copy to skb
	5) free stats

With the help of nla_reserve() we can operate on skb->data directly,
thus avoiding all these steps except 2).

So, before this patch:

	// copy *stats to skb->data
	int mk_reply(skb, ..., struct taskstats *stats);

	fill_pid(stats);
	mk_reply(skb, ..., stats);

After:
	// return a pointer to skb->data
	struct taskstats *mk_reply(skb, ...);

	stat = mk_reply(skb, ...);
	fill_pid(stats);

Shrinks taskatsks.o by 162 bytes.

A stupid benchmark (send one million TASKSTATS_CMD_ATTR_PID) shows the

		real user sys
	before:
		4.02 0.06 3.96
		4.02 0.04 3.98
		4.02 0.04 3.97
	after:
		3.86 0.08 3.78
		3.88 0.10 3.77
		3.89 0.09 3.80

but this looks suspiciously good.

Signed-off-by: Oleg Nesterov <20b70f0af00562e63758b9ee42012ecc96c58590@tv-sign.ru>
Acked-by: Shailabh Nagar <4143e32b9d97ce835bdf36a4bf4c150a5c75e208@watson.ibm.com>
Cc: Balbir Singh <65a1aed538f36fed73d8c45e9ddfc585ce9f4abf@in.ibm.com>
Cc: Jay Lan <d86a88ad23d08353494752844a9fd09490196754@sgi.com>
Cc: Thomas Graf <17c2d8920621522552b392f72d8fdb4d1e866b44@suug.ch>
Signed-off-by: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@osdl.org>
Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@osdl.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs