Re: Linux 2.6.29

Nick Piggin
2009-04-04T05:56:08Z

On Friday 03 April 2009 13:16:08 Linus Torvalds wrote:
>
> On Thu, 2 Apr 2009, Jeff Garzik wrote:
> >
> > The most interesting thing I found: the SSD does 80 MB/s for the first ~1 GB
> > or so, then slows down dramatically. After ~2GB, it is down to 32 MB/s.
> > After ~4GB, it reaches a steady speed around 23 MB/s.
>
> Are you sure that isn't an effect of double and triple indirect blocks
> etc? The metadata updates get more complex for the deeper indirect blocks.
>
> Or just our page cache lookup? Maybe our radix tree thing hits something
> stupid. Although it sure shouldn't be _that_ noticeable.

Hmm, I don't know what you have in mind. page cache lookup should be
several orders of magnitude faster than a disk can write the pages out?

Dirty/writeout/clean cycle still has to lock the radix tree to change
tags, but that's really not going to be significantly contended (nor
does it synchronise with simple lookups).