Re: missing madvise functionality

[Rik van Riel <riel@redhat.com>]

Nick Piggin wrote:

> Oh, also: something like this patch would help out MADV_DONTNEED, as it
> means it can run concurrently with page faults. I think the locking will
> work (but needs forward porting).

Ironically, your patch decreases throughput on my quad core
test system, with Jakub's test case.

MADV_DONTNEED, my patch, 10000 loops  (14k context switches/second)

real    0m34.890s
user    0m17.256s
sys     0m29.797s


MADV_DONTNEED, my patch & your patch, 10000 loops  (50 context 
switches/second)

real    1m8.321s
user    0m20.840s
sys     1m55.677s

I suspect it's moving the contention onto the page table lock,
in zap_pte_range().  I guess that the thread private memory
areas must be living right next to each other, in the same
page table lock regions :)

For more real world workloads, like the MySQL sysbench one,
I still suspect that your patch would improve things.

Time to move back to debugging other stuff, though.

Andrew, it would be nice if our patches could cook in -mm
for a while.  Want me to change anything before submitting?

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