On Tue, 23 Apr 2013, Zheng Liu wrote: > Date: Tue, 23 Apr 2013 17:19:28 +0800 > From: Zheng Liu <gnehzuil.liu@xxxxxxxxx> > To: Jan Kara <jack@xxxxxxx> > Cc: Lukas Czerner <lczerner@xxxxxxxxxx>, linux-mm@xxxxxxxxx, > linux-kernel@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, > linux-ext4@xxxxxxxxxxxxxxx > Subject: Re: [PATCH v3 17/18] ext4: make punch hole code path work with > bigalloc > > On Sat, Apr 20, 2013 at 03:42:41PM +0200, Jan Kara wrote: > > On Tue 09-04-13 11:14:26, Lukas Czerner wrote: > > > Currently punch hole is disabled in file systems with bigalloc > > > feature enabled. However the recent changes in punch hole patch should > > > make it easier to support punching holes on bigalloc enabled file > > > systems. > > > > > > This commit changes partial_cluster handling in ext4_remove_blocks(), > > > ext4_ext_rm_leaf() and ext4_ext_remove_space(). Currently > > > partial_cluster is unsigned long long type and it makes sure that we > > > will free the partial cluster if all extents has been released from that > > > cluster. However it has been specifically designed only for truncate. > > > > > > With punch hole we can be freeing just some extents in the cluster > > > leaving the rest untouched. So we have to make sure that we will notice > > > cluster which still has some extents. To do this I've changed > > > partial_cluster to be signed long long type. The only scenario where > > > this could be a problem is when cluster_size == block size, however in > > > that case there would not be any partial clusters so we're safe. For > > > bigger clusters the signed type is enough. Now we use the negative value > > > in partial_cluster to mark such cluster used, hence we know that we must > > > not free it even if all other extents has been freed from such cluster. > > > > > > This scenario can be described in simple diagram: > > > > > > |FFF...FF..FF.UUU| > > > ^----------^ > > > punch hole > > > > > > . - free space > > > | - cluster boundary > > > F - freed extent > > > U - used extent > > > > > > Also update respective tracepoints to use signed long long type for > > > partial_cluster. > > The patch looks OK. You can add: > > Reviewed-by: Jan Kara <jack@xxxxxxx> > > > > Just a minor nit - sometimes you use 'signed long long', sometimes 'long > > long int', sometimes just 'long long'. In kernel we tend to always use just > > 'long long' so it would be good to clean that up. > > Another question is that in patch 01/18 invalidatepage signature is > changed from > int (*invalidatepage) (struct page *, unsigned long); > to > void (*invalidatepage) (struct page *, unsigned int, unsigned int); > > The argument type is changed from 'unsigned long' to 'unsigned int'. My > question is why we need to change it. > > Thanks, > - Zheng > Hi Zheng, this was changed on Hugh Dickins request because it makes it clearer that those args are indeed intended to be offsets within a page (0..PAGE_CACHE_SIZE). Even though PAGE_CACHE_SIZE can be defined as unsigned long, this is only for convenience. Here is quote from Hugh: " They would be defined as unsigned long so that they can be used in masks like ~(PAGE_SIZE - 1), and behave as expected on addresses, without needing casts to be added all over. We do not (currently!) expect PAGE_SIZE or PAGE_CACHE_SIZE to grow beyond an unsigned int - but indeed they can be larger than what's held in an unsigned short (look no further than ia64 or ppc64). For more reassurance, see include/linux/highmem.h, which declares zero_user_segments() and others: unsigned int (well, unsigned with the int implicit) for offsets within a page. Hugh " I should probably mention that in the description. Thanks! -Lukas -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
