Messages in this thread | | | Date | Wed, 07 Jul 2010 08:42:53 +0800 | From | Tao Ma <> | Subject | Re: [PATCH 1/2] ocfs2: Zero the tail cluster when extending past i_size v2 |
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Joel Becker wrote: > On Tue, Jul 06, 2010 at 03:54:58PM +0800, Tao Ma wrote: > >> On 07/06/2010 03:17 PM, Joel Becker wrote: >> >>>>> + /* Is there a cluster to zero? */ >>>>> + if (!p_cpos) >>>>> + goto out; >>>>> >>>> For unwritten extent, we also need to clear the pages? If yes, the >>>> solution doesn't complete if we have 2 unwritten extent, one >>>> contains i_size while one passes i_size. Here we only clear the >>>> pages for the 1st unwritten extent and leave the 2nd one untouched. >>>> >>> We probably don't need to zero unwritten extents. We cannot >>> have an extent past i_size, can we? >>> >> we can. AFAICS, ocfs2_change_file_space will allocate unwritten >> extents and does't change i_size. >> > > Oh, you're right. We need to walk the entire extent range > between i_size and pos and figure out what needs CoW. This needs to > happen no matter what. > Actually we can only have unwritten extents after i_size and it shouldn't hurt you in this case. So do we really need to CoW all the unwritten extents? All I want to say is that since they are unwritten, they should also mean 'zero' for the user space. So can we just need to skip clearing pages if i_size is in an unwritten extent? > >>> But you dropped the check for pos_blkno alignment. >>> Unconditionally adding the +1 doesn't seem like a good idea. >>> >> You can add it as you wish. >> I just thought that you add one more extra cluster if pos_blkno >> isn't aligned so as to zero blocks in [pos_cpos_start_block, >> pos_blkno). >> But As I said in the comments, you will soon write pos_blkno(it also >> needs to be CoW since it is within this refcounted extent), so if we >> can CoW it out now, maybe we have a chance to not call >> ocfs2_refcount_cow later. >> > > I'd much rather let the write handle its own contiguousness. If > we get lucky, that CoW melds with our CoW. If we don't get lucky, isn't > it better to have the newly changed area be fully contiguous rather than > have the first extent of it not be and then the remaining extents be? > fair enough.
Regards, Tao
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