From 4c21e2f2441dc5fbb957b030333f5a3f2d02dea7 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Sat, 29 Oct 2005 18:16:40 -0700 Subject: [PATCH] mm: split page table lock Christoph Lameter demonstrated very poor scalability on the SGI 512-way, with a many-threaded application which concurrently initializes different parts of a large anonymous area. This patch corrects that, by using a separate spinlock per page table page, to guard the page table entries in that page, instead of using the mm's single page_table_lock. (But even then, page_table_lock is still used to guard page table allocation, and anon_vma allocation.) In this implementation, the spinlock is tucked inside the struct page of the page table page: with a BUILD_BUG_ON in case it overflows - which it would in the case of 32-bit PA-RISC with spinlock debugging enabled. Splitting the lock is not quite for free: another cacheline access. Ideally, I suppose we would use split ptlock only for multi-threaded processes on multi-cpu machines; but deciding that dynamically would have its own costs. So for now enable it by config, at some number of cpus - since the Kconfig language doesn't support inequalities, let preprocessor compare that with NR_CPUS. But I don't think it's worth being user-configurable: for good testing of both split and unsplit configs, split now at 4 cpus, and perhaps change that to 8 later. There is a benefit even for singly threaded processes: kswapd can be attacking one part of the mm while another part is busy faulting. Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/frv/mm/pgalloc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'arch/frv/mm/pgalloc.c') diff --git a/arch/frv/mm/pgalloc.c b/arch/frv/mm/pgalloc.c index 4eaec0f3525..2c67dfe5a6b 100644 --- a/arch/frv/mm/pgalloc.c +++ b/arch/frv/mm/pgalloc.c @@ -87,14 +87,14 @@ static inline void pgd_list_add(pgd_t *pgd) if (pgd_list) pgd_list->private = (unsigned long) &page->index; pgd_list = page; - page->private = (unsigned long) &pgd_list; + set_page_private(page, (unsigned long)&pgd_list); } static inline void pgd_list_del(pgd_t *pgd) { struct page *next, **pprev, *page = virt_to_page(pgd); next = (struct page *) page->index; - pprev = (struct page **) page->private; + pprev = (struct page **)page_private(page); *pprev = next; if (next) next->private = (unsigned long) pprev; -- cgit v1.2.3