Messages in this thread |  | | Date | Thu, 12 Dec 2013 16:37:11 -0500 | From | Rik van Riel <> | Subject | Re: [RFC PATCH 2/3] Add tunable to control THP behavior |
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On 12/12/2013 01:00 PM, Alex Thorlton wrote: > This part of the patch adds a tunable to > /sys/kernel/mm/transparent_hugepage called threshold. This threshold > determines how many pages a user must fault in from a single node before > a temporary compound page is turned into a THP.
> +++ b/mm/huge_memory.c > @@ -44,6 +44,9 @@ unsigned long transparent_hugepage_flags __read_mostly = > (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)| > (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG); > > +/* default to 1 page threshold for handing out thps; maintains old behavior */ > +static int transparent_hugepage_threshold = 1;
I assume the motivation for writing all this code is that "1" was not a good value in your tests.
That makes me wonder, why should 1 be the default value with your patches?
If there is a better value, why should we not use that?
What is the upside of using a better value?
What is the downside?
Is there a value that would to bound the downside, so it is almost always smaller than the upside?
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