Hi Zach,
Thanks for reviewing this patch.
On Tue, Jul 03, 2012 at 10:57:35AM -0700, Zach Brown wrote:
>
> >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. :-)
>
> >+ /* 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)) {
>
> >- if (allocated<= EXT4_EXT_ZERO_LEN&&
> >+ if (allocated<= sbi->s_extent_zeroout_len&&
> > (EXT4_EXT_MAY_ZEROOUT& split_flag)) {
>
> > } 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
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