Messages in this thread | | | Date | Wed, 25 Oct 2006 00:19:50 +0200 | From | Pavel Machek <> | Subject | Re: [PATCH] Use extents for recording what swap is allocated. |
| |
Hi!
> > > > Switch from bitmaps to using extents to record what swap is allocated; > > > > they make more efficient use of memory, particularly where the allocated > > > > storage is small and the swap space is large. > > > > > > As I said before, I like the overall idea, but I have a bunch of > > > comments. > > > > Okay, if Rafael likes it... lets take a look. > > > > First... what is the _worst case_ overhead? AFAICT extents are very > > good at the best case, but tend to suck for the worst case...? > > 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). 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/
| |