From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f53.google.com (mail-wm0-f53.google.com [74.125.82.53]) by kanga.kvack.org (Postfix) with ESMTP id AE8B96B0005 for ; Mon, 25 Jan 2016 14:50:28 -0500 (EST) Received: by mail-wm0-f53.google.com with SMTP id b14so97699553wmb.1 for ; Mon, 25 Jan 2016 11:50:28 -0800 (PST) Received: from e06smtp12.uk.ibm.com (e06smtp12.uk.ibm.com. [195.75.94.108]) by mx.google.com with ESMTPS id i7si406152wmf.59.2016.01.25.11.50.26 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 25 Jan 2016 11:50:27 -0800 (PST) Received: from localhost by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 25 Jan 2016 19:50:26 -0000 Received: from b06cxnps4075.portsmouth.uk.ibm.com (d06relay12.portsmouth.uk.ibm.com [9.149.109.197]) by d06dlp01.portsmouth.uk.ibm.com (Postfix) with ESMTP id 033D017D8056 for ; Mon, 25 Jan 2016 19:50:33 +0000 (GMT) Received: from d06av09.portsmouth.uk.ibm.com (d06av09.portsmouth.uk.ibm.com [9.149.37.250]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u0PJoPk09503110 for ; Mon, 25 Jan 2016 19:50:25 GMT Received: from d06av09.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av09.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u0PJoOOp007456 for ; Mon, 25 Jan 2016 12:50:24 -0700 From: Christian Borntraeger Subject: [PATCH v3] mm/debug_pagealloc: Ask users for default setting of debug_pagealloc Date: Mon, 25 Jan 2016 20:50:46 +0100 Message-Id: <1453751446-97135-1-git-send-email-borntraeger@de.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: linux-kernel@vger.kernel.org Cc: peterz@infradead.org, heiko.carstens@de.ibm.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, Dave Jones , Christian Borntraeger , Joonsoo Kim since commit 031bc5743f158 ("mm/debug-pagealloc: make debug-pagealloc boottime configurable") CONFIG_DEBUG_PAGEALLOC is by default not adding any page debugging. This resulted in several unnoticed bugs, e.g. https://lkml.kernel.org/g/<569F5E29.3090107@de.ibm.com> or https://lkml.kernel.org/g/<56A20F30.4050705@de.ibm.com> as this behaviour change was not even documented in Kconfig. Let's provide a new Kconfig symbol that allows to change the default back to enabled, e.g. for debug kernels. This also makes the change obvious to kernel packagers. Let's also change the Kconfig description for CONFIG_DEBUG_PAGEALLOC, to indicate that there are two stages of overhead. Cc: Joonsoo Kim Cc: Andrew Morton Signed-off-by: Christian Borntraeger --- v2 -> v3: tab/whitespace, off->n (Paul Bolle) remove "If unsure say no." v1 -> v2: change Kconfig help to indicate, that CONFIG_DEBUG_PAGEALLOC is not for free, even if disabled mm/Kconfig.debug | 18 ++++++++++++++++-- mm/page_alloc.c | 6 +++++- 2 files changed, 21 insertions(+), 3 deletions(-) diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug index 957d3da..a0c136a 100644 --- a/mm/Kconfig.debug +++ b/mm/Kconfig.debug @@ -16,8 +16,8 @@ config DEBUG_PAGEALLOC select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC ---help--- Unmap pages from the kernel linear mapping after free_pages(). - This results in a large slowdown, but helps to find certain types - of memory corruption. + Depending on runtime enablement, this results in a small or large + slowdown, but helps to find certain types of memory corruption. For architectures which don't enable ARCH_SUPPORTS_DEBUG_PAGEALLOC, fill the pages with poison patterns after free_pages() and verify @@ -26,5 +26,19 @@ config DEBUG_PAGEALLOC that would result in incorrect warnings of memory corruption after a resume because free pages are not saved to the suspend image. + By default this option will have a small overhead, e.g. by not + allowing the kernel mapping to be backed by large pages on some + architectures. Even bigger overhead comes when the debugging is + enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc + command line parameter. + +config DEBUG_PAGEALLOC_ENABLE_DEFAULT + bool "Enable debug page memory allocations by default?" + default n + depends on DEBUG_PAGEALLOC + ---help--- + Enable debug page memory allocations by default? This value + can be overridden by debug_pagealloc=off|on. + config PAGE_POISONING bool diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 9d666df..933def7 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -479,7 +479,8 @@ void prep_compound_page(struct page *page, unsigned int order) #ifdef CONFIG_DEBUG_PAGEALLOC unsigned int _debug_guardpage_minorder; -bool _debug_pagealloc_enabled __read_mostly; +bool _debug_pagealloc_enabled __read_mostly + = IS_ENABLED(CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT); bool _debug_guardpage_enabled __read_mostly; static int __init early_debug_pagealloc(char *buf) @@ -490,6 +491,9 @@ static int __init early_debug_pagealloc(char *buf) if (strcmp(buf, "on") == 0) _debug_pagealloc_enabled = true; + if (strcmp(buf, "off") == 0) + _debug_pagealloc_enabled = false; + return 0; } early_param("debug_pagealloc", early_debug_pagealloc); -- 2.3.0 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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