Messages in this thread |  | | | Date | Wed, 25 Oct 2006 10:11:35 +0200 | | From | Pavel Machek <> | | Subject | Re: [PATCH] Use extents for recording what swap is allocated. |
Hi!
> > > That's right. In using this, we're relying on the fact that the swap > > > allocator tries to act sensibly. I've only seen worse case performance > > > when a user had two swap devices with the same priority (striped), but > > > that was a bug. :) > > > > Ok, but if the allocator somehow manages to stripe between two swap > > devices, what happens? > > > > IIRC original code was something like .1% overhead (8bytes per 4K, or > > something?), bitmaps should be even better. If it is 1% in worst case, > > that's probably okay, but it would be bad if it had overhead bigger > > than 10times original code (worst case). > > 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?
In particular, how much swap space can we have before we run out of low memory? What is the overhead compared to bitmaps? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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