There are local complaints that filtering out only zero pages is slow. I
found that is_zero_page was inefficient. It checks if the page contains any
non-zero bytes - one byte at a time.
Improve performance by checking for non-zero data 64 bits at a time. Also,
unroll the loop for additional performance.
Did testing in x86_64 mode on an Intel Xeon x5560 system with 18GB RAM.
Executed:
time makedumpfile -d 1 /proc/vmcore <destination>
The amount of time taken in User space was reduced by 75%. The total time to
dump memory was reduced by 28%.
is_zero_page
Signed-off-by: Marc Milgram <mmilgram at redhat.com>
---
diff --git a/makedumpfile.h b/makedumpfile.h
index 3d270c6..0f211c4 100644
--- a/makedumpfile.h
+++ b/makedumpfile.h
@@ -1634,10 +1634,27 @@ static inline int
is_zero_page(unsigned char *buf, long page_size)
{
size_t i;
+ unsigned long long *vect = (unsigned long long *) buf;
+ long page_len = page_size / (sizeof(unsigned long long));
- for (i = 0; i < page_size; i++)
- if (buf[i])
+ for (i = 0; i < page_len; i+=8) {
+ if (vect[i])
return FALSE;
+ if (vect[i+1])
+ return FALSE;
+ if (vect[i+2])
+ return FALSE;
+ if (vect[i+3])
+ return FALSE;
+ if (vect[i+4])
+ return FALSE;
+ if (vect[i+5])
+ return FALSE;
+ if (vect[i+6])
+ return FALSE;
+ if (vect[i+7])
+ return FALSE;
+ }
return TRUE;
}
