Re: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Andrew Morton wrote:
Nick Piggin <[email protected]> wrote:

Despite what people were trying to tell me at Ottawa, this patch
set really does add quite a lot of complexity to the page
allocator, and it seems to be increasingly only of benefit to
dynamically allocating hugepages and memory hot unplug.


Remember that Rohit is seeing ~10% variation between runs of scientific
software, and that his patch to use higher-order pages to preload the
percpu-pages magazines fixed that up.  I assume this means that it provided
up to 10% speedup, which is a lot.


OK, I wasn't aware of this. I wonder what other approaches we could
try to add a bit of colour to our pages? I bet something simple like
trying to hand out alternate odd/even pages per task might help.

But the patch caused page allocator fragmentation and several reports of
gigE Tx buffer allocation failures, so I dropped it.

We think that Mel's patches will allow us to reintroduce Rohit's
optimisation.


If that is the case, do we really want to make such sacrifices
for the huge machines that want these things? What about just
making an extra zone for easy-to-reclaim things to live in?

This could possibly even be resized at runtime according to
demand with the memory hotplug stuff (though I haven't been
following that).

Don't take this as criticism of the actual implementation or its
effectiveness.



But yes, adding additional complexity is a black mark, and these patches
add quite a bit.  (Ditto the fine-looking adaptive readahead patches, btw).


They do look quite fine. They seem to get their claws pretty deep
into page reclaim, but I guess that is to be expected if we want
to increase readahead smarts much more.

However, I'm hoping bits of that can be merged at a time, and
interfaces and page reclaim stuff can be discussed and the best
option taken. No such luck with these patches AFAIKS - simply
adding another level of page groups, and another level of
heuristics to the page allocator is going to hurt. By definition.
I do wonder why zones can't be used... though I'm sure there are
good reasons.

--
SUSE Labs, Novell Inc.

Send instant messages to your online friends http://au.messenger.yahoo.com -
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux