Dave Hansen wrote: > On 05/11/2013 06:23 PM, Kirill A. Shutemov wrote: > > This patch introduces radix_tree_preload_count(). It allows to > > preallocate nodes enough to insert a number of *contiguous* elements. > > Would radix_tree_preload_contig() be a better name, then? Yes. Will rename. > ... > > On 64-bit system: > > For RADIX_TREE_MAP_SHIFT=3, old array size is 43, new is 107. > > For RADIX_TREE_MAP_SHIFT=4, old array size is 31, new is 63. > > For RADIX_TREE_MAP_SHIFT=6, old array size is 21, new is 30. > > > > On 32-bit system: > > For RADIX_TREE_MAP_SHIFT=3, old array size is 21, new is 84. > > For RADIX_TREE_MAP_SHIFT=4, old array size is 15, new is 46. > > For RADIX_TREE_MAP_SHIFT=6, old array size is 11, new is 19. > > > > On most machines we will have RADIX_TREE_MAP_SHIFT=6. > > Thanks for adding that to the description. The array you're talking > about is just pointers, right? > > 107-43 = 64. So, we have 64 extra pointers * NR_CPUS, plus 64 extra > radix tree nodes that we will keep around most of the time. On x86_64, > that's 512 bytes plus 64*560 bytes of nodes which is ~35k of memory per CPU. > > That's not bad I guess, but I do bet it's something that some folks want > to configure out. Please make sure to call out the actual size cost in > bytes per CPU in future patch postings, at least for the common case > (64-bit non-CONFIG_BASE_SMALL). I will add this to the commit message: On most machines we will have RADIX_TREE_MAP_SHIFT=6. In this case, on 64-bit system the per-CPU feature overhead is for preload array: (30 - 21) * sizeof(void*) = 72 bytes plus, if the preload array is full (30 - 21) * sizeof(struct radix_tree_node) = 9 * 560 = 5040 bytes total: 5112 bytes on 32-bit system the per-CPU feature overhead is for preload array: (19 - 11) * sizeof(void*) = 32 bytes plus, if the preload array is full (19 - 11) * sizeof(struct radix_tree_node) = 8 * 296 = 2368 bytes total: 2400 bytes --- Is it good enough? I probably, will add !BASE_SMALL dependency to TRANSPARENT_HUGEPAGE_PAGECACHE config option. > > > Since only THP uses batched preload at the , we disable (set max preload > > to 1) it if !CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE. This can be changed > > in the future. > > "at the..." Is there something missing in that sentence? at the moment :) > No major nits, so: > > Acked-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Thanks! -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>