Messages in this thread | | | Date | Tue, 21 Jun 2011 01:23:19 +0800 | From | Cong Wang <> | Subject | Re: [PATCH 2/3] mm: make the threshold of enabling THP configurable |
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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: >> +config TRANSPARENT_HUGEPAGE_THRESHOLD >> + depends on TRANSPARENT_HUGEPAGE >> + 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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