Messages in this thread | | | Date | Fri, 23 Mar 2007 23:39:17 -0800 | From | Andrew Morton <> | Subject | Re: [patch] rfc: introduce /dev/hugetlb |
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On Sat, 24 Mar 2007 00:11:32 -0700 "Ken Chen" <kenchen@google.com> wrote:
> On 3/23/07, Andrew Morton <akpm@linux-foundation.org> wrote: > > a) Ken observes that obtaining private hugetlb memory via hugetlbfs > > involves "fuss". > > > > b) the libhugetlbfs maintainers then go off and implement a no-fuss way of > > doing this. > > Hmm, what started this thread was libhugetlbfs maintainer complained > how "fuss" it was to create private hugetlb mapping and suggested an > even bigger kernel change with pagetable_operations API.
OK. I wasn't paying particularly close attention. But my rant still stands ;)
> The new API > was designed with an end goal of introduce /dev/hugetlb (as one of the > feature, they might be thinking more). What motivated me here is to > point out that we can achieve the same goal of having a /dev/hugetlb > with existing hugetlbfs infrastructure and the implementation is > relatively straightforward. What it also buys us is a bit more > flexibility to the end user who wants to use the interface directly.
OK.
Why is it a "fuss" to do this with hugetlbfs files, btw?
Having read back through the thread, the only substantiation I can really see is
The pagetable_operations API opens up possibilities to do some additional (and completely sane) things. For example, I have a patch that alters the character device code below to make use of a hugetlb ZERO_PAGE. This eliminates almost all the up-front fault time, allowing pages to be COW'ed only when first written to. We cannot do things like this with hugetlbfs anymore because we have a set of complex semantics to preserve.
Why is this actually a useful feature?
What does "complex semantics to preserve" mean?
I dunno. I see a lot of code flying around, but comparatively little effort to describe the actual problems which we're trying to solve.
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