Re: [PATCH v2 6/6] mm, hugetlb: improve page-fault scalability

[Joonsoo Kim <iamjoonsoo.kim@lge.com>]

On Fri, Jan 31, 2014 at 09:36:46AM -0800, Davidlohr Bueso wrote:
> From: Davidlohr Bueso <davidlohr@hp.com>
> 
> The kernel can currently only handle a single hugetlb page fault at a time.
> This is due to a single mutex that serializes the entire path. This lock
> protects from spurious OOM errors under conditions of low of low availability
> of free hugepages. This problem is specific to hugepages, because it is
> normal to want to use every single hugepage in the system - with normal pages
> we simply assume there will always be a few spare pages which can be used
> temporarily until the race is resolved.
> 
> Address this problem by using a table of mutexes, allowing a better chance of
> parallelization, where each hugepage is individually serialized. The hash key
> is selected depending on the mapping type. For shared ones it consists of the
> address space and file offset being faulted; while for private ones the mm and
> virtual address are used. The size of the table is selected based on a compromise
> of collisions and memory footprint of a series of database workloads.

Hello,

Thanks for doing this patchset. :)
Just one question!
Why do we need a separate hash key depending on the mapping type?

Thanks.

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