Ingo Molnar wrote:

For every 64-bit Fedora box there's more than seven 32-bit boxes. I 
think 32-bit is going to live with us far longer than many thought, so 
we might as well make it work better. Both HIGHMEM and HIGHPTE is the 
default on many distro kernels, which pushes the kmap infrastructure 
quite a bit.

I don't think anybody would argue against numbers, but just that there
are not many big 32-bit SMPs anymore. And if Bill Irwin didn't fix the
kmap problem back then, it would be interesting to see a system and
workload where it actually is a bottleneck.

Not that I'm against any patch to improve scalability, if it doesn't
hurt single-threaded performance ;)

the problem is that everything that was easy to migrate was migrated off 
kmap() already - and it's exactly those hard cases that cannot be 
converted (like the pagecache use) which is the most frequent kmap() 
users.

Which pagecache use? file_read_actor()?

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