Re: [RFC] gfp_mask for address_space

[Alexander Viro <viro@math.psu.edu>]

On Mon, 4 Dec 2000, Stephen C. Tweedie wrote:

> However, it doesn't actually fix all of the problems.  We still have
> balance_dirty() deadlocks even if we avoid memory allocation loops.

I know. However, these are somewhat easier to kill. E.g. we could give
weights to devices (normal => 0, loopback over file on device of level
n => n+1) and split bdflush into per-weight threads. Then we have an
obvious hierarchy (activity of bdflush[n] can't lead to new dirty bh
of weight n and above).
 
> The problem right now is that the balance_dirty() inside the nbd
> server can result in it attempting to flush out dirty nbd buffers, so
> we have the nbd device blocked on the nbd server, the nbd server
> dirtying local disk buffer_heads, and the dirty buffer code blocking
> on other dirty nbd buffers.)

Ditto for loop and the same method can be applied... 

I'm actually more interested in experimenting with bitmaps in page
cache - making it GFP_BUFFER should be deadlock-safe, AFAICS, and
ext2/balloc.c would benefit big way from switching to that...
							Cheers,
								Al

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