On Sat, 30 Jun 2012 17:07:54 +0800 Jiang Liu <jiang.liu@xxxxxxxxxx> wrote: > From: Xishi Qiu <qiuxishi@xxxxxxxxxx> > > On architectures with CONFIG_HUGETLB_PAGE_SIZE_VARIABLE set, such as Itanium, > pageblock_order is a variable with default value of 0. It's set to the right > value by set_pageblock_order() in function free_area_init_core(). > > But pageblock_order may be used by sparse_init() before free_area_init_core() > is called along path: > sparse_init() > ->sparse_early_usemaps_alloc_node() > ->usemap_size() > ->SECTION_BLOCKFLAGS_BITS > ->((1UL << (PFN_SECTION_SHIFT - pageblock_order)) * > NR_PAGEBLOCK_BITS) > > The uninitialized pageblock_size will cause memory wasting because usemap_size() > returns a much bigger value then it's really needed. > > For example, on an Itanium platform, > sparse_init() pageblock_order=0 usemap_size=24576 > free_area_init_core() before pageblock_order=0, usemap_size=24576 > free_area_init_core() after pageblock_order=12, usemap_size=8 > > That means 24K memory has been wasted for each section, so fix it by calling > set_pageblock_order() from sparse_init(). > > ... > > --- a/mm/sparse.c > +++ b/mm/sparse.c > @@ -485,6 +485,9 @@ void __init sparse_init(void) > struct page **map_map; > #endif > > + /* Setup pageblock_order for HUGETLB_PAGE_SIZE_VARIABLE */ > + set_pageblock_order(); > + > /* > * map is using big page (aka 2M in x86 64 bit) > * usemap is less one page (aka 24 bytes) It's a bit ugly calling set_pageblock_order() from both sparse_init() and from free_area_init_core(). Can we find a single place from which to call it? It looks like here: --- a/init/main.c~a +++ a/init/main.c @@ -514,6 +514,7 @@ asmlinkage void __init start_kernel(void __stop___param - __start___param, -1, -1, &unknown_bootoption); + set_pageblock_order(); jump_label_init(); /* would do the trick? (free_area_init_core is __paging_init and set_pageblock_order() is __init. I'm too lazy to work out if that's wrong) -- 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>