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 --- mm/swap_state.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'mm/swap_state.c') diff --git a/mm/swap_state.c b/mm/swap_state.c index 132164f7d0a..cafc1edcbeb 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -83,7 +83,7 @@ static int __add_to_swap_cache(struct page *page, swp_entry_t entry, page_cache_get(page); SetPageLocked(page); SetPageSwapCache(page); - page->private = entry.val; + set_page_private(page, entry.val); total_swapcache_pages++; pagecache_acct(1); } @@ -126,8 +126,8 @@ void __delete_from_swap_cache(struct page *page) BUG_ON(PageWriteback(page)); BUG_ON(PagePrivate(page)); - radix_tree_delete(&swapper_space.page_tree, page->private); - page->private = 0; + radix_tree_delete(&swapper_space.page_tree, page_private(page)); + set_page_private(page, 0); ClearPageSwapCache(page); total_swapcache_pages--; pagecache_acct(-1); @@ -197,7 +197,7 @@ void delete_from_swap_cache(struct page *page) { swp_entry_t entry; - entry.val = page->private; + entry.val = page_private(page); write_lock_irq(&swapper_space.tree_lock); __delete_from_swap_cache(page); -- cgit v1.2.3