Andrew Morton wrote:
On Thu, 03 May 2007 11:32:23 +1000 Nick Piggin <[EMAIL PROTECTED]> wrote:void fastcall unlock_page(struct page *page) { + VM_BUG_ON(!PageLocked(page)); smp_mb__before_clear_bit(); - if (!TestClearPageLocked(page)) - BUG();- smp_mb__after_clear_bit(); - wake_up_page(page, PG_locked);+ ClearPageLocked(page); + if (unlikely(test_bit(PG_waiters, &page->flags))) { + clear_bit(PG_waiters, &page->flags); + wake_up_page(page, PG_locked); + } }Why is that significantly faster than plain old wake_up_page(), which tests waitqueue_active()?
Because it needs fewer barriers and doesn't touch random a random hash cacheline in the fastpath. -- SUSE Labs, Novell Inc. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
