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/swapfile.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) (limited to 'mm/swapfile.c') diff --git a/mm/swapfile.c b/mm/swapfile.c index 510f003..8970c0b 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -61,7 +61,7 @@ void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page) swp_entry_t entry; down_read(&swap_unplug_sem); - entry.val = page->private; + entry.val = page_private(page); if (PageSwapCache(page)) { struct block_device *bdev = swap_info[swp_type(entry)].bdev; struct backing_dev_info *bdi; @@ -69,8 +69,8 @@ void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page) /* * If the page is removed from swapcache from under us (with a * racy try_to_unuse/swapoff) we need an additional reference - * count to avoid reading garbage from page->private above. If - * the WARN_ON triggers during a swapoff it maybe the race + * count to avoid reading garbage from page_private(page) above. + * If the WARN_ON triggers during a swapoff it maybe the race * condition and it's harmless. However if it triggers without * swapoff it signals a problem. */ @@ -294,7 +294,7 @@ static inline int page_swapcount(struct page *page) struct swap_info_struct *p; swp_entry_t entry; - entry.val = page->private; + entry.val = page_private(page); p = swap_info_get(entry); if (p) { /* Subtract the 1 for the swap cache itself */ @@ -339,7 +339,7 @@ int remove_exclusive_swap_page(struct page *page) if (page_count(page) != 2) /* 2: us + cache */ return 0; - entry.val = page->private; + entry.val = page_private(page); p = swap_info_get(entry); if (!p) return 0; @@ -1042,7 +1042,7 @@ int page_queue_congested(struct page *page) BUG_ON(!PageLocked(page)); /* It pins the swap_info_struct */ if (PageSwapCache(page)) { - swp_entry_t entry = { .val = page->private }; + swp_entry_t entry = { .val = page_private(page) }; struct swap_info_struct *sis; sis = get_swap_info_struct(swp_type(entry)); -- cgit v1.1