http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50636
--- Comment #8 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-10-07 08:25:37 UTC --- (In reply to comment #4) > Right now alloc_page will (usually) allocate in GGC_QUIRE_SIZE * G.pagesize > chunks, but release_pages will munmap individual pages immediately during > collection (well, using one munmap if there are consecutive free pages, but > that is not very likely everything is going to be freed from the whole 1MB > page). > Guess we could do MADV_DONTNEED on the individual pages immediately and if we > have consecutive 1MB region all free, munmap it (or, decide about that based > on > how many free pages we have etc.). I guess doubling GGC_QUIRE_SIZE is > reasonable too. I guess that's a good idea, separate from the 2mb page issue. Do other systems beside Linux have MADV_DONTNEED? I suppose popular host platforms include Windows and Mac OS today. It also seems that we release pages we put on the free list when allocating a GGC_QUIRE_SIZE * G.pagesize chunk (which we only do if we allocate exactly one page, otherwise we map a random amount of memory). Would probably be interesting to add some instrumentation code to see how the map/munmap patterns look like ... But yes, it seems we should unmap only in groups but advise in smaller chunks.
