Re: [PATCH] Use extents for recording what swap is allocated.

[Pavel Machek <pavel@ucw.cz>]

Hi!

> > > With the code I have in Suspend2 (which is what I'm working towards),
> > > the value includes the swap_type, so there's no overlap. Assuming the
> > > swap allocator does it's normal thing and swap allocated is contiguous,
> > > you'll probably end up with two extents: one containing the swap
> > > allocated on the first device, and the other containing the swap
> > > allocated on the second device. So (with the current version), striping
> > > would use 6 * sizeof(unsigned long) instead of 3 * sizeof(unsigned
> > > long).
> > 
> > And now, can you do same computation assuming the swap allocator goes
> > completely crazy, and free space is in 1-page chunks?
> 
> The worst case is 3 * sizeof(unsigned long) *
> number_of_swap_extents_allocated bytes.

Okay, so if we got 4GB of swap space, thats 1MB swap pages, worst case
is you have one extent per page, on x86-64 that's 24MB. +kmalloc
overhead, I assume?

And you do linear walks over those extents, leading to O(n^2)
algorithm, no? That has bitten us before...
									Pavel
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