Hi!
A small update.
Patching mm/filemap.c is not necessary in order to get the improved performance! It's sufficient to remove roundup_pow_of_two from |get_init_ra_size ...
So a simple one-liner changes to picture dramatically. But why ?!?!?
roundup_pow_of_two() uses fls() and ia64 has buggy fls() implementation [ seems that David fixed it but patch is not in the mainline yet]:
http://www.mail-archive.com/linux-ia64@vger.kernel.org/msg01196.html
That would also explain why you couldn't reproduce the problem on ia32 Xeon machines.
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