John McCorquodale <[email protected]> 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 -- [email protected] -- Speaking for myself only -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
