2.6.17-...: looong writeouts

[Alexey Dobriyan <adobriyan@gmail.com>]

Immediate problem: from time to time post 2.6.17 kernel [1] decides that it
really really needs disk.

	[kernel compilation goes as usual]
	  CC [M]  fs/xfs/xfs_inode.o
	[compilation blocks for ~10 seconds, disk LED is red]
	[then it continues]

Again, from time to time saving 2k file makes vi inoperational for same
period.

Scheduler is CFQ, fs is reiserfs mounted with noatime, notail. 2.6.17-rc
and 2.6.17 kernels were OK.

It occured only several times in 4 hours.

[1] 2.6.17-95eaa5fa8eb2c345244acd5f65b200b115ae8c65 to be precise


Probably related problem below:

During 2.6.17-rc cycle CFQ subjectively became less F.

	[   unpacking  ]
	[kernel tarball]
		.
		.
		.
		.
		.
		.
		.		[:wq on little file]
		.
		.
		.
		.
		.
		.
	[              ]

IIRC, on 2.6.16 that :wq took say 0.5 sec, on late 2.6.17-rc it was
several times slower. I don't have numbers but it was psychologically
noticeable, but not BFD.

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