Re: [PATCH] mm: cache largest vma

[KOSAKI Motohiro]

(11/1/13 4:17 PM), Davidlohr Bueso wrote:
> While caching the last used vma already does a nice job avoiding
> having to iterate the rbtree in find_vma, we can improve. After
> studying the hit rate on a load of workloads and environments,
> it was seen that it was around 45-50% - constant for a standard
> desktop system (gnome3 + evolution + firefox + a few xterms),
> and multiple java related workloads (including Hadoop/terasort),
> and aim7, which indicates it's better than the 35% value documented
> in the code.
>
> By also caching the largest vma, that is, the one that contains
> most addresses, there is a steady 10-15% hit rate gain, putting
> it above the 60% region. This improvement comes at a very low
> overhead for a miss. Furthermore, systems with !CONFIG_MMU keep
> the current logic.

I'm slightly surprised this cache makes 15% hit. Which application
get a benefit? You listed a lot of applications, but I'm not sure
which is highly depending on largest vma.


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