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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:
    >> +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.

    Thanks.
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