Re: [PATCH 0/3]HTLB mapping for drivers (take 2)

[Eric Munson <linux-mm@mgebm.net>]

On Mon, Aug 17, 2009 at 11:24 PM, Alexey Korolev<akorolev@infradead.org> wrote:
> Hi,
>
> The patch set listed below provides device drivers with the ability to
> map memory regions to user space via HTLB interfaces.
>
> Why we need it?
> Device drivers often need to map memory regions to user-space to allow
> efficient data handling in user mode. Involving hugetlb mapping may
> bring performance gain if mapped regions are relatively large. Our tests
> showed that it is possible to gain up to 7% performance if hugetlb
> mapping is enabled. In my case involving hugetlb starts to make sense if
> buffer is more or equal to 4MB. Since typically, device throughput
> increase over time there are more and more reasons to involve huge pages
> to remap large regions.
> For example hugetlb remapping could be important for performance of Data
> acquisition systems (logic analyzers, DSO), Network monitoring systems
> (packet capture), HD video capture/frame buffer  and probably other.
>
> How it is implemented?
> Implementation and idea is very close to what is already done in
> ipc/shm.c.
> We create file on hugetlbfs vfsmount point and populate file with pages
> we want to mmap. Then we associate hugetlbfs file mapping with file
> mapping we want to access.
>
> So typical procedure for mapping of huge pages to userspace by drivers
> should be:
> 1 Allocate some huge pages
> 2 Create file on vfs mount of hugetlbfs
> 3 Add pages to page cache of mapping associated with hugetlbfs file
> 4 Replace file's mapping with the hugetlbfs file mapping
> ..............
> 5 Remove pages from page cache
> 6 Remove hugetlbfs file
> 7 Free pages
> (Please find example in following messages)
>
> Detailed description is given in the following messages.
> Thanks a lot to Mel Gorman who gave good advice and code prototype and
> Stephen Donnelly for assistance in description composing.
>
> Alexey

It sounds like this patch set working towards the same goal as my
MAP_HUGETLB set.  The only difference I see is you allocate huge page
at a time and (if I am understanding the patch) fault the page in
immediately, where MAP_HUGETLB only faults pages as needed.  Does the
MAP_HUGETLB patch set provide the functionality that you need, and if
not, what can be done to provide what you need?

Eric

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