Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754630Ab1ECTIL (ORCPT ); Tue, 3 May 2011 15:08:11 -0400 Received: from mo-p00-ob.rzone.de ([81.169.146.162]:54932 "EHLO mo-p00-ob.rzone.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754317Ab1ECTIK (ORCPT ); Tue, 3 May 2011 15:08:10 -0400 X-RZG-AUTH: :P2EQZWCpfu+qG7CngxMFH1J+zrwiavkK6tmQaLfmwtM48/lq0M7oFPE= X-RZG-CLASS-ID: mo00 Date: Tue, 3 May 2011 21:08:06 +0200 From: Olaf Hering To: linux-kernel@vger.kernel.org, kexec@lists.infradead.org Cc: akpm@linux-foundation.org Subject: [PATCH] add hook to read_from_oldmem() to check for non-ram pages Message-ID: <20110503190806.GA12485@aepfle.de> References: <20110407095646.GA30788@aepfle.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20110407095646.GA30788@aepfle.de> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3917 Lines: 120 The balloon driver in a Xen guest frees guest pages and marks them as mmio. When the kernel crashes and the crash kernel attempts to read the oldmem via /proc/vmcore a read from ballooned pages will generate 100% load in dom0 because Xen asks qemu-dm for the page content. Since the reads come in as 8byte requests each ballooned page is tried 512 times. With this change a hook can be registered which checks wether the given pfn is really ram. The hook has to return a value > 0 for ram pages, a value < 0 on error (because the hypercall is not known) and 0 for non-ram pages. This will reduce the time to read /proc/vmcore. Without this change a 512M guest with 128M crashkernel region needs 200 seconds to read it, with this change it takes just 2 seconds. Signed-off-by: Olaf Hering --- fs/proc/vmcore.c | 50 ++++++++++++++++++++++++++++++++++++++++++--- include/linux/crash_dump.h | 5 ++++ 2 files changed, 52 insertions(+), 3 deletions(-) Index: linux-2.6.39-rc5/fs/proc/vmcore.c =================================================================== --- linux-2.6.39-rc5.orig/fs/proc/vmcore.c +++ linux-2.6.39-rc5/fs/proc/vmcore.c @@ -18,6 +18,7 @@ #include #include #include +#include #include #include @@ -35,6 +36,44 @@ static u64 vmcore_size; static struct proc_dir_entry *proc_vmcore = NULL; +/* returns > 0 for RAM pages, 0 for non-RAM pages, < 0 on error */ +static int (*oldmem_pfn_is_ram)(unsigned long pfn); +static DECLARE_WAIT_QUEUE_HEAD(oldmem_fn_waitq); +static atomic_t oldmem_fn_refcount = ATOMIC_INIT(0); + +void register_oldmem_pfn_is_ram(int (*fn)(unsigned long)) +{ + if (oldmem_pfn_is_ram == NULL) + oldmem_pfn_is_ram = fn; +} + +void unregister_oldmem_pfn_is_ram(void) +{ + wait_event(oldmem_fn_waitq, atomic_read(&oldmem_fn_refcount) == 0); + oldmem_pfn_is_ram = NULL; + wmb(); +} + +static int pfn_is_ram(unsigned long pfn) +{ + int (*fn)(unsigned long); + /* pfn is ram unless fn() checks pagetype */ + int ret = 1; + + atomic_inc(&oldmem_fn_refcount); + smp_mb__after_atomic_inc(); + fn = oldmem_pfn_is_ram; + if (fn) + ret = fn(pfn); + if (atomic_dec_and_test(&oldmem_fn_refcount)) + wake_up(&oldmem_fn_waitq); + + return ret; +} + +EXPORT_SYMBOL_GPL(register_oldmem_pfn_is_ram); +EXPORT_SYMBOL_GPL(unregister_oldmem_pfn_is_ram); + /* Reads a page from the oldmem device from given offset. */ static ssize_t read_from_oldmem(char *buf, size_t count, u64 *ppos, int userbuf) @@ -55,9 +94,14 @@ static ssize_t read_from_oldmem(char *bu else nr_bytes = count; - tmp = copy_oldmem_page(pfn, buf, nr_bytes, offset, userbuf); - if (tmp < 0) - return tmp; + /* if pfn is not ram, return zeros for spares dump files */ + if (pfn_is_ram(pfn) == 0) + memset(buf, 0, nr_bytes); + else { + tmp = copy_oldmem_page(pfn, buf, nr_bytes, offset, userbuf); + if (tmp < 0) + return tmp; + } *ppos += nr_bytes; count -= nr_bytes; buf += nr_bytes; Index: linux-2.6.39-rc5/include/linux/crash_dump.h =================================================================== --- linux-2.6.39-rc5.orig/include/linux/crash_dump.h +++ linux-2.6.39-rc5/include/linux/crash_dump.h @@ -66,6 +66,11 @@ static inline void vmcore_unusable(void) if (is_kdump_kernel()) elfcorehdr_addr = ELFCORE_ADDR_ERR; } + +#define HAVE_OLDMEM_PFN_IS_RAM 1 +extern void register_oldmem_pfn_is_ram(int (*fn)(unsigned long)); +extern void unregister_oldmem_pfn_is_ram(void); + #else /* !CONFIG_CRASH_DUMP */ static inline int is_kdump_kernel(void) { return 0; } #endif /* CONFIG_CRASH_DUMP */ -- 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/