On Wed, 2011-03-30 at 06:24 +0800, Andrew Morton wrote: > On Tue, 29 Mar 2011 08:54:14 +0800 > Shaohua Li <shaohua.li@xxxxxxxxx> wrote: > > > -struct percpu_counter vm_committed_as; > > +struct percpu_counter vm_committed_as ____cacheline_internodealigned_in_smp; > > Why ____cacheline_internodealigned_in_smp? That's pretty aggressive. > > afacit the main benefit from this will occur if the read-only > vm_committed_as.counters lands in the same cacheline as some > write-frequently storage. vm_committed_as can be frequently updated in some workloads too. > But that's a complete mad guess and I'd prefer not to have to guess. is below updated patch better to you? Make some variables have correct alignment/section to avoid cache issue. In a workload which heavily does mmap/munmap, the variables will be used frequently. Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx> --- mm/mmap.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) Index: linux/mm/mmap.c =================================================================== --- linux.orig/mm/mmap.c 2011-03-30 08:45:05.000000000 +0800 +++ linux/mm/mmap.c 2011-03-30 08:59:23.000000000 +0800 @@ -84,10 +84,14 @@ pgprot_t vm_get_page_prot(unsigned long } EXPORT_SYMBOL(vm_get_page_prot); -int sysctl_overcommit_memory = OVERCOMMIT_GUESS; /* heuristic overcommit */ -int sysctl_overcommit_ratio = 50; /* default is 50% */ +int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS; /* heuristic overcommit */ +int sysctl_overcommit_ratio __read_mostly = 50; /* default is 50% */ int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT; -struct percpu_counter vm_committed_as; +/* + * Make sure vm_committed_as in one cacheline and not cacheline shared with + * other variables. It can be updated by several CPUs frequently. + */ +struct percpu_counter vm_committed_as ____cacheline_internodealigned_in_smp; /* * Check that a process has enough memory to allocate a new virtual -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>