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authorOlaf Hering <olaf@aepfle.de>2011-05-26 16:25:54 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-05-26 17:12:37 -0700
commit997c136f518c5debd63847e78e2a8694f56dcf90 (patch)
treeac2ff48901be3e6834757675dcc177732e034a9f
parent98bc93e505c03403479c6669c4ff97301cee6199 (diff)
downloadvexpress-lsk-997c136f518c5debd63847e78e2a8694f56dcf90.tar.gz
fs/proc/vmcore.c: add hook to read_from_oldmem() to check for non-ram pages
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 <olaf@aepfle.de> Cc: Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/proc/vmcore.c52
-rw-r--r--include/linux/crash_dump.h5
2 files changed, 54 insertions, 3 deletions
diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index 74802bc5ded..cd99bf55765 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -35,6 +35,46 @@ 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
+ * The called function has to take care of module refcounting.
+ */
+static int (*oldmem_pfn_is_ram)(unsigned long pfn);
+
+int register_oldmem_pfn_is_ram(int (*fn)(unsigned long pfn))
+{
+ if (oldmem_pfn_is_ram)
+ return -EBUSY;
+ oldmem_pfn_is_ram = fn;
+ return 0;
+}
+EXPORT_SYMBOL_GPL(register_oldmem_pfn_is_ram);
+
+void unregister_oldmem_pfn_is_ram(void)
+{
+ oldmem_pfn_is_ram = NULL;
+ wmb();
+}
+EXPORT_SYMBOL_GPL(unregister_oldmem_pfn_is_ram);
+
+static int pfn_is_ram(unsigned long pfn)
+{
+ int (*fn)(unsigned long pfn);
+ /* pfn is ram unless fn() checks pagetype */
+ int ret = 1;
+
+ /*
+ * Ask hypervisor if the pfn is really ram.
+ * A ballooned page contains no data and reading from such a page
+ * will cause high load in the hypervisor.
+ */
+ fn = oldmem_pfn_is_ram;
+ if (fn)
+ ret = fn(pfn);
+
+ return ret;
+}
+
/* 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 +95,15 @@ static ssize_t read_from_oldmem(char *buf, size_t count,
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 sparse 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;
diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
index 088cd4ace4e..74054074e87 100644
--- a/include/linux/crash_dump.h
+++ b/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 int register_oldmem_pfn_is_ram(int (*fn)(unsigned long pfn));
+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 */