于 2011年06月21日 01:28, Rik van Riel 写道:
On 06/20/2011 01:19 PM, Cong Wang wrote:
于 2011年06月21日 01:10, Rik van Riel 写道:
On 06/20/2011 01:07 PM, Cong Wang wrote:
于 2011年06月21日 00:58, Mel Gorman 写道:
On Tue, Jun 21, 2011 at 12:34:28AM +0800, Amerigo Wang wrote:
transparent_hugepage=never should mean to disable THP completely,
otherwise we don't have a way to disable THP completely.
The design is broken.
I don't get why it's broken. Why would the user be prevented from
enabling it at runtime?
We need to a way to totally disable it, right? Otherwise, when I
configure
THP in .config, I always have THP initialized even when I pass "=never".
For me, if you don't provide such way to disable it, it is not flexible.
I meet this problem when I try to disable THP in kdump kernel, there is
no user of THP in kdump kernel, THP is a waste for kdump kernel. This is
why I need to find a way to totally disable it.
What you have not explained yet is why having THP
halfway initialized (but not used, and without a
khugepaged thread) is a problem at all.
Why is it a problem for you?
It occupies some memory, memory is valuable in kdump kernel (usually
only 128M). :) Since I am sure no one will use it, why do I still need
to initialize it at all?
Lets take a look at how much memory your patches end
up saving.
By bailing out earlier in hugepage_init, you end up
saving 3 sysfs objects, one slab cache and a hash
table with 1024 pointers. That's a total of maybe
10kB of memory on a 64 bit system.
I'm not convinced that a 10kB memory reduction is
worth the price of never being able to enable
transparent hugepages when a system is booted with
THP disabled...
Even if it is really 10K, why not save it since it doesn't
much effort to make this. ;) Not only memory, but also time,
this could also save a little time to initialize the kernel.
For me, the more serious thing is the logic, there is
no way to totally disable it as long as I have THP in .config
currently. This is why I said the design is broken.
Thanks.
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