On 8/13/12 1:49 PM, Theodore Ts'o wrote: > On Mon, Aug 13, 2012 at 11:02:08AM -0500, Eric Sandeen wrote: >> >> Looks ok to me; I think this just further optimizes what was done >> in >> >> 8a57d9d61a6e361c7bb159dda797672c1df1a691 >> ext4: check for a good block group before loading buddy pages >> >> correct? > > Yes, that's right; it's a further optimization. > > I can think of an additional optimization where if we are reading the > block bitmap for block group N, and the block bitmap for block group > N+1 hasn't been read before (so we don't have buddy bitmap stats), and > the block bitmap for bg N+1 is adjacent for bg N, we should read both > at the same time. (And this could be generalized for N+2, N+3, etc.) > > I'm not entirely sure whether it's worth the effort, but I suspect for > very full file systems, it might be very well be. This is a more > general case of the problem where most people only benchmark mostly > empty file systems, and my experience has been that above 70-80% > utilization, our performance starts to fall off. And while disk space > is cheap, it's not _that_ cheap, and there are always customers who > insist on using file systems up to a utilization of 99%, and expect > the same performance as when the file system was freshly formated. :-( I did some tests w/ very large filesystems, fallocating 1T at a time until full. ext4 tended to fall down pretty badly towards the end. Anything that can reduce the time it takes to find free blocks as a very large filesystem fills would probably be useful.... -eric > - Ted > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
