Hi Zach,

Thanks for reviewing this patch.

On Tue, Jul 03, 2012 at 10:57:35AM -0700, Zach Brown wrote:

quoted

workload frequently does a uninitialized extent conversion.  Thus, now
we set it to 256 (1MB chunk), and put it into super block in order to
adjust it dynamically in sysfs.

It's a bit of a tangent, but this caught my eye.

Oh, actually now the default value is set to 1MB in this patch.  But I
think maybe other users want to change this value.  So I add an interface
in sysfs to adjust dynaimically.  Certainly it is convenient for me to do
the above tests. :-)

quoted

+	/* If extent has less than 2*s_extent_zeroout_len zerout directly */
+	if (ee_len<= 2*sbi->s_extent_zeroout_len&&
 	(EXT4_EXT_MAY_ZEROOUT&  split_flag)) {

quoted

-		if (allocated<= EXT4_EXT_ZERO_LEN&&
+		if (allocated<= sbi->s_extent_zeroout_len&&
 		(EXT4_EXT_MAY_ZEROOUT&  split_flag)) {

quoted

 		} else if ((map->m_lblk - ee_block + map->m_len<
-			   EXT4_EXT_ZERO_LEN)&&
+			   sbi->s_extent_zeroout_len)&&

I'd be worried about having to verify that nothing bad happened if these
sbi s_extent_zeroout_len references could see different values if they
raced with a sysfs update.  Can they do that?

Maybe avoid the risk all together and have an on-stack copy that's only
referenced once at the start?

I don't think 's_extent_zeroout_len' is updated frequently by user, but
using an on-stack copy quite can avoid the risk.  I will fix it if most
of all think that this patch is useful and can be applied.

Regards,
Zheng