Fix zfs_dirty_data_max overflow on 32-bit

On 32 bit, the calculation of zfs_dirty_data_max from phymem will overflow, causing it to be smaller than zfs_dirty_data_sync, and will cause txg being delayed while no one write to disk. The end result is horrendous write speed. On 4G ram 32-bit VM, before this patch, simple dd results in ~7MB/s. Now it can reach speed on par with 64-bit VM. Signed-off-by: Chunwei Chen <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes openzfs#3973
ryao · Dec 3, 2015 · bc9ad13 · bc9ad13
1 parent 8085cb2
commit bc9ad13
Showing 1 changed file with 2 additions and 2 deletions.
diff --git a/module/zfs/arc.c b/module/zfs/arc.c
@@ -5478,11 +5478,11 @@ arc_init(void)
 	 * zfs_dirty_data_max_max (default 25% of physical memory).
 	 */
 	if (zfs_dirty_data_max_max == 0)
-		zfs_dirty_data_max_max = physmem * PAGESIZE *
+		zfs_dirty_data_max_max = (uint64_t)physmem * PAGESIZE *
 		    zfs_dirty_data_max_max_percent / 100;
 
 	if (zfs_dirty_data_max == 0) {
-		zfs_dirty_data_max = physmem * PAGESIZE *
+		zfs_dirty_data_max = (uint64_t)physmem * PAGESIZE *
 		    zfs_dirty_data_max_percent / 100;
 		zfs_dirty_data_max = MIN(zfs_dirty_data_max,
 		    zfs_dirty_data_max_max);