Messages in this thread | | | From | Andi Kleen <> | Subject | Re: Transparent Hugepage Nit | Date | Tue, 15 Jan 2013 13:26:58 -0800 |
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John McCorquodale <mcq@rockgeek.org> writes:
> Suppose a hugepage-aligned mmap(MAP_ANONYMOUS) mapping has been madvise()d > HUGEPAGE. If a subeqeuent call to mremap() grows the mapping and has to > move the mapping, the hugepage-alignment is not preserved in the choice of > new address (in 3.7.2). > > I can workaround this by doing a 1-hugepage-oversized remap to find a new > aligned address and then size it back down MREMAP_FIXED, but that's probably > a lot of frags to 4k pages and back that aren't necessary. > > Should it not be the case that mremap(MAYMOVE) on something advised hugepage > ALWAYS chooses a hugepage-aligned address? This would be handy when doing the > initial allocation too: mmap, madvise, mremap (to the same size) to get > alignment.
The hole searching currently doesn't know anything about transparent huge pages. There were some discussions on fixing it. But it's essentially a trade off between memory fragmentation and huge page optimization: aggressively aligning to 2MB can lose address space in holes.
Usually if the program uses large enough mappings and enough memory it shouldn't be a problem.
-Andi -- ak@linux.intel.com -- Speaking for myself only
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