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SubjectRe: [PATCH 2/3] mm: make the threshold of enabling THP configurable
于 2011年06月21日 00:59, Dave Hansen 写道:
> On Tue, 2011-06-21 at 00:34 +0800, Amerigo Wang wrote:
>> + int "The minimal threshold of enabling Transparent Hugepage"
>> + range 512 8192
>> + default "512"
>> + help
>> + The threshold of enabling Transparent Huagepage automatically,
>> + in Mbytes, below this value, Transparent Hugepage will be disabled
>> + by default during boot.
> It makes some sense to me that there would _be_ a threshold, simply
> because you need some space to defragment things. But, I can't imagine
> any kind of user having *ANY* kind of idea what to set this to. Could
> we add some text to this? Maybe:
> Transparent hugepages are created by moving other pages out of
> the way to create large, contiguous swaths of free memory.
> However, some memory on a system can not be easily moved. It is
> likely on small systems that this unmovable memory will occupy a
> large portion of total memory, which makes even attempting to
> create transparent hugepages very expensive.
> If you are unsure, set this to the smallest possible value.
> To override this at boot, use the $FOO boot command-line option.

Yeah, I totally agree to improve the help message as you said,
please forgive a non-English speaker. ;)

> I'm also not sure putting a ceiling on this makes a lot of sense.
> What's the logic behind that? I know it would be a mess to expose it to
> users, but shouldn't this be a per-zone limit, logically? Seems like a
> 8GB system would have similar issues to a two-numa-node 16GB system.

I am not sure about this, since I am new to THP, I just replaced
the hard-code 512 with a Kconfig var. But I am certainly open
to improve this as you said if Andrea agrees.

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