On Wed, 2007-11-14 at 21:06 +1100, Benjamin Herrenschmidt wrote: > On Wed, 2007-11-14 at 10:26 +0100, Martin Schwidefsky wrote: > > That patch allows processes to have different number of page table > > levels, 31 bit processes have 2 levels (2GB), normal 64 bit processes > > have 3 levels (4TB) and really big 64 bit processes can have 4 levels > > (8PB). The downgrade of a page table to use less levels than the > > parent > > process is done in arch_pick_mmap_layout. The upgrade is done by using > > the arch_rebalance_pgtables call. I've considered using the > > arch_get_unmapped_area but got scared by the indirection in > > get_unmapped_area: > > > > get_area = current->mm->get_unmapped_area; > > if (file && file->f_op && file->f_op->get_unmapped_area) > > get_area = file->f_op->get_unmapped_area; > > addr = get_area(file, addr, len, pgoff, flags); > > Don't be, it's really only hugetlb and other arch specific stuff that > hook in here on platforms with an MMU (It's also used by /dev/mem etc... > for mmu-less platforms but you don't care). I find 8 places where a get_unmapped_area function pointer is used: ipc/shm.c: shm_get_unmapped_area / shm_file_operations drivers/char/mem.c: get_unmapped_area_mem / mem_fops & kmem_fops drivers/video/fbmem.c: get_fb_unmapped_area / fb_fops drivers/pci/proc.c: get_pci_unmapped_area / proc_bus_pci_operations fs/hugetlbfs/inode.c: hugetlb_get_unmapped_area / hugetlbfs_file_operations fs/bad_inode.c: bad_file_get_unmapped_area / bad_file_ops fs/ramfs/file-nommu.c: ramfs_nommu_get_unmapped_area / ramfs_file_operations arch/powerpc/platforms/cell/spufs/file.c: spufs_get_unmapped_area / spufs_mem_fops They all either have an arch override, call get_unmapped_area again or are not relevant. So it should be possible to do the upgrade in arch_get_unmapped_area. I still have my doubts though, all future uses of the get_unmapped_area pointer have to be checked and I feel it is easier to understand to do the upgrade / rebalance of the page table at the end of get_unmapped_area where every caller of mmap is guaranteed to pass through. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. - To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
