On Wed, 8 Sep 2010, Andreas Dilger wrote:
> On 2010-09-08, at 10:59, Lukas Czerner wrote:
> > +static inline int sb_issue_zeroout(struct super_block *sb,
> > + sector_t block, sector_t nr_blocks)
> > +{
> > + block <<= (sb->s_blocksize_bits - 9);
> > + nr_blocks <<= (sb->s_blocksize_bits - 9);
> > + return blkdev_issue_zeroout(sb->s_bdev, block, nr_blocks, GFP_KERNEL,
> > + BLKDEV_IFL_WAIT | BLKDEV_IFL_BARRIER);
> > +}
>
> While I can understand that we might need a barrier for this (to avoid
> it being reordered with later writes that are using these blocks), I'm
> not sure it needs to wait for previous IO to complete.
We are waiting for submitted bios to finish. Especially in my patch it
is needed, because I need to know how long it takes to get this IO on
disk do determine next schedule time, depending on the IO load. I am not
sure about this, but when it would not wait it will complete fairly
quickly and my "IO throttling" code would be useless.
And if I am wrong, and you are really convinced that it should not wait,
what about sb_issue_discard(), it is also waiting for completion, is it
ok?
Regards.
-Lukas
>
> Cheers, Andreas
>
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