On 04/11/2010 03:08 PM, Ingo Molnar wrote:
No one is insisting the patches aren't intrusive. We're insisting they
bring a real benefit. I think Linus' main objection was that hugetlb
wouldn't work due to fragmentation, and I think we've demonstrated that
antifrag/compaction do allow hugetlb to work even during a fragmenting
workload running in parallel.
As i understood it i think Linus had three main objections:
1- the improvements were only shown in specialistic environments
(virtualization, servers)
Servers are not specialized workloads, and neither is virtualization.
If we have to justify everything based on the desktop experience we'd
have no 4096 core support, fibre channel and 10GbE drivers, a zillion
architectures etc.
2- complexity
No arguing with that.
The important thing to realize is that the working set of the 'desktop' is
_not_ independent of RAM size: it just fills up RAM to the 'typical average
RAM size'. That is around 2 GB today. In 5-10 years it will be at 16 GB.
Applications will just bloat up to that natural size. They'll use finer
default resolutions, larger internal caches, etc. etc.
Well, if this happens we'll be ready.
'git grep' is a pagecache workload, not anonymous memory, so it shouldn't
see any improvement. [...]
Indeed, git grep is read() based.
Right.
[...] I imagine git will see a nice speedup if we get hugetlb for
pagecache, at least for read-only workloads that don't hash all the time.
Shouldnt that already be the case today? The pagecache is in the kernel where
we have things 2MB mapped. Git read()s it into the same [small] buffer again
and again, so the only 'wide' address space access it does is within the
kernel, to the 2MB mapped pagecache pages.
If you 'git grep pattern $commit' instead, you'll be reading out of
mmap()ed git packs. Much of git memory access goes through that. To
get the benefit of hugetlb there, we'd need to run khugepaged on
pagecache, and align file vmas on 2MB boundaries.
We'll also get executables and shared objects mapped via large pages
this way, the ELF ABI is already set up to align sections on 2MB boundaries.
--
error compiling committee.c: too many arguments to function
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