Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757544AbZKJWCo (ORCPT ); Tue, 10 Nov 2009 17:02:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756391AbZKJWCn (ORCPT ); Tue, 10 Nov 2009 17:02:43 -0500 Received: from mk-filter-3-a-1.mail.uk.tiscali.com ([212.74.100.54]:26807 "EHLO mk-filter-3-a-1.mail.uk.tiscali.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755546AbZKJWCm (ORCPT ); Tue, 10 Nov 2009 17:02:42 -0500 X-Trace: 284590392/mk-filter-3.mail.uk.tiscali.com/B2C/$b2c-THROTTLED-DYNAMIC/b2c-CUSTOMER-DYNAMIC-IP/79.69.44.180/None/hugh.dickins@tiscali.co.uk X-SBRS: None X-RemoteIP: 79.69.44.180 X-IP-MAIL-FROM: hugh.dickins@tiscali.co.uk X-SMTP-AUTH: X-MUA: X-IP-BHB: Once X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AjkFAB5y+UpPRSy0/2dsb2JhbACBTt0khD4E X-IronPort-AV: E=Sophos;i="4.44,718,1249254000"; d="scan'208";a="284590392" Date: Tue, 10 Nov 2009 22:02:46 +0000 (GMT) From: Hugh Dickins X-X-Sender: hugh@sister.anvils To: Andrew Morton cc: Izik Eidus , Andrea Arcangeli , Peter Zijlstra , Christoph Lameter , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 5/6] mm: stop ptlock enlarging struct page In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2400 Lines: 54 CONFIG_DEBUG_SPINLOCK adds 12 or 16 bytes to a 32- or 64-bit spinlock_t, and CONFIG_DEBUG_LOCK_ALLOC adds another 12 or 24 bytes to it: lockdep enables both of those, and CONFIG_LOCK_STAT adds 8 or 16 bytes to that. When 2.6.15 placed the split page table lock inside struct page (usually sized 32 or 56 bytes), only CONFIG_DEBUG_SPINLOCK was a possibility, and we ignored the enlargement (but fitted in CONFIG_GENERIC_LOCKBREAK's 4 by letting the spinlock_t occupy both page->private and page->mapping). Should these debugging options be allowed to double the size of a struct page, when only one minority use of the page (as a page table) needs to fit a spinlock in there? Perhaps not. Take the easy way out: switch off SPLIT_PTLOCK_CPUS when DEBUG_SPINLOCK or DEBUG_LOCK_ALLOC is in force. I've sometimes tried to be cleverer, kmallocing a cacheline for the spinlock when it doesn't fit, but given up each time. Falling back to mm->page_table_lock (as we do when ptlock is not split) lets lockdep check out the strictest path anyway. And now that some arches allow 8192 cpus, use 999999 for infinity. (What has this got to do with KSM swapping? It doesn't care about the size of struct page, but may care about random junk in page->mapping - to be explained separately later.) Signed-off-by: Hugh Dickins --- mm/Kconfig | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- mm4/mm/Kconfig 2009-11-04 10:52:58.000000000 +0000 +++ mm5/mm/Kconfig 2009-11-04 10:53:13.000000000 +0000 @@ -161,11 +161,13 @@ config PAGEFLAGS_EXTENDED # Default to 4 for wider testing, though 8 might be more appropriate. # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock. # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes. +# DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page. # config SPLIT_PTLOCK_CPUS int - default "4096" if ARM && !CPU_CACHE_VIPT - default "4096" if PARISC && !PA20 + default "999999" if ARM && !CPU_CACHE_VIPT + default "999999" if PARISC && !PA20 + default "999999" if DEBUG_SPINLOCK || DEBUG_LOCK_ALLOC default "4" # -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/