On Fri, 12 Dec 2008 11:48:29 +1100 Paul Mackerras [off-list ref] wrote:

Andrew Morton writes:

quoted

quoted

+#if (8 * THREAD_SIZE) > PAGE_SIZE
 	max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
+#else
+	max_threads = mempages * (PAGE_SIZE / (8 * THREAD_SIZE));
+#endif

The expression you've chosen here can be quite inacccurate, because
((PAGE_SIZE / (8 * THREAD_SIZE)) is a small number.  The way to
preserve accuracy is

The assumption is that THREAD_SIZE is a power of 2, as is PAGE_SIZE.

I think Yuri should be increasing THREAD_SIZE for the larger page
sizes he's implementing, because we have on-stack arrays whose size
depends on the page size.  I suspect that having THREAD_SIZE less than
1/8 of PAGE_SIZE risks stack overflows, and the better fix is for Yuri
to make sure THREAD_SIZE is at least 1/8 of PAGE_SIZE.  (In fact, more
may be needed - someone should work out what fraction is actually
needed.)

OK, yes.

It's the MAX_BUF_PER_PAGE arrays which will hurt.  iirc they nest
three-deep on some codepaths.