Re: More convenient way to grab hugepage memory

From: Christoph Hellwig
Date: Thu May 13 2004 - 02:50:46 EST

On Thu, May 13, 2004 at 03:55:20PM +1000, David Gibson wrote:
> Andrew, please apply:
> At present, getting a block of (quasi-) anonymous memory mapping with
> hugepages is a slightly convoluted process, involving creating a dummy
> file in a hugetlbfs filesystem. In particular that means finding
> where such a filesystem is mounted, for which there is no standard
> mechanism. Getting hugepage SysV shm segments is easier, just requing
> the SHM_HUGETLB flag. This patch adds an analagous MAP_HUGETLB mmap()
> flag to easily request that a block of anonymous memory come from
> hugepages.
> [The MAP_HUGETLB flag has the side effect that MAP_SHARED semantics
> will apply, even if MAP_PRIVATE is specific - but that's no different
> to explicitly mapping hugetlbfs].

Please don't do this. It's messing all over sensitive codepathes in the
kernel, creating special cases and bloat of what you could with simple a
simpe hugetlb_mmap() wrapper ala (pseudocode)

fd = open(file in hugetlbfs)

mmap(.., fd, ...)

in some library. The hugetlbfs implementation was chosen exactly because
if kept the impact of hugetlb pages down to normal kernel codepathes.

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