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 --- include/linux/buffer_head.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'include/linux/buffer_head.h') diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h index 88af42f5e04a..c937d6e65502 100644 --- a/include/linux/buffer_head.h +++ b/include/linux/buffer_head.h @@ -126,8 +126,8 @@ BUFFER_FNS(Eopnotsupp, eopnotsupp) /* If we *know* page->private refers to buffer_heads */ #define page_buffers(page) \ ({ \ - BUG_ON(!PagePrivate(page)); \ - ((struct buffer_head *)(page)->private); \ + BUG_ON(!PagePrivate(page)); \ + ((struct buffer_head *)page_private(page)); \ }) #define page_has_buffers(page) PagePrivate(page) @@ -219,7 +219,7 @@ static inline void attach_page_buffers(struct page *page, { page_cache_get(page); SetPagePrivate(page); - page->private = (unsigned long)head; + set_page_private(page, (unsigned long)head); } static inline void get_bh(struct buffer_head *bh) -- cgit v1.2.3