Dave Hansen wrote: > On 03/22/2013 02:47 AM, Kirill A. Shutemov wrote: > > Dave Hansen wrote: > >> On 03/14/2013 10:50 AM, Kirill A. Shutemov wrote: > >>> +#define RADIX_TREE_PRELOAD_NR 512 /* For THP's benefit */ > >> > >> This eventually boils down to making the radix_tree_preload array > >> larger. Do we really want to do this unconditionally if it's only for > >> THP's benefit? > > > > It will be useful not only for THP. Batching can be useful to solve > > scalability issues. > > Still, it seems like something that little machines with no THP support > probably don't want to pay the cost for. Perhaps you could enable it > for THP||NR_CPUS>$FOO.
Okay, I'll disable it for !THP. We always can change it if we'll find good candidate for batching. > >> For those of us too lazy to go compile a kernel and figure this out in > >> practice, how much bigger does this make the nodes[] array? > > > > We have three possible RADIX_TREE_MAP_SHIFT: > > > > #ifdef __KERNEL__ > > #define RADIX_TREE_MAP_SHIFT (CONFIG_BASE_SMALL ? 4 : 6) > > #else > > #define RADIX_TREE_MAP_SHIFT 3 /* For more stressful testing */ > > #endif > > > > 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. > > Could you stick that in your patch description? Will do. > The total cost is "array size" * sizeof(void*) * NR_CPUS, right? Correct. -- Kirill A. Shutemov -- 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/
