ocfs2: Zero the tail cluster when extending past i_size v2
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From: Tao Ma on 6 Jul 2010 20:50 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Joel Becker on 6 Jul 2010 22:10
On Wed, Jul 07, 2010 at 08:42:53AM +0800, Tao Ma wrote: > > 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? We can certainly have unwritten extents in the middle too ;-) I've just reworked the entire ocfs2_zero_extend() logic to skip unwritten extents and CoW refcounted ones. We have to CoW for nonsparse anyway, so we needed this logic. We do need to walk the entire range, just in case there are extents anywhere between i_size and pos. Patches coming as soon as it stops breaking. Joel -- Life's Little Instruction Book #3 "Watch a sunrise at least once a year." Joel Becker Consulting Software Developer Oracle E-mail: joel.becker(a)oracle.com Phone: (650) 506-8127 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |