4.2-rc2: hitting "file-max limit 8192 reached"

[Dave Hansen <dave.hansen@intel.com>]

My laptop has been behaving strangely with 4.2-rc2.  Once I log in to my
X session, I start getting all kinds of strange errors from applications
and see this in my dmesg:

	VFS: file-max limit 8192 reached

Could this be from CONFIG_DEFERRED_STRUCT_PAGE_INIT=y?  files_init()
seems top be sizing files_stat.max_files from memory sizes.

vfs_caches_init() uses nr_free_pages() to figure out what the "current
kernel size" is in early boot.  *But* since we have not freed most of
our memory, nr_free_pages() is low and makes us calculate the reserve as
if the kernel we huge.

Adding some printk's confirms this.  Broken kernel:

	vfs_caches_init() mempages: 4026972
	vfs_caches_init() reserve: 4021629
	vfs_caches_init() mempages (after reserve minus): 5343
	files_init() n: 2137
	files_init() files_stat.max_files: 8192

Working kernel:

	vfs_caches_init() mempages: 4026972
	vfs_caches_init() reserve: 375
	vfs_caches_init() mempages2: 4026597
	files_init() n: 1610638
	files_init() files_stat.max_files: 1610638

Do we have an alternative to call instead of nr_free_pages() in
vfs_caches_init()?

I guess we could save off 'nr_initialized' in memmap_init_zone() and
then use "nr_initialized - nr_free_pages()", but that seems a bit hackish.

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