Re: 2.5.67-mm3

Andrew Morton
2003-04-15T05:35:37Z

William Lee Irwin III <wli@holomorphy.com> wrote:
>
> On Mon, Apr 14, 2003 at 09:55:41PM -0700, Andrew Morton wrote:
> > Sort-of. The code is doing two things.
> > a) Make sure that all the relevant pte's are established in the correct
> > state so we don't take a fault while holding the subsequent atomic kmap.
> > This is just an optimisation. If we _do_ take the fault while holding
> > an atomic kmap, we fall back to sleeping kmap, and do the whole copy
> > again. It almost never happens.
>
> This is the easy part; we're basically just prefaulting.

btw, this may sound like a lot of futzing about, but the other day I
timed four concurrent instances of

dd if=/dev/zero of=$i bs=1 count=1M

on the four-way. 2.5 ran eight times faster than 2.4. 2.4's kmap_lock
contention was astonishing.