2014-02-03 0:21 GMT+09:00, Matthew Wilcox [off-list ref]:

On Sun, Feb 02, 2014 at 08:16:24AM -0700, Matthew Wilcox wrote:

quoted

On Sun, Feb 02, 2014 at 02:41:34PM +0900, Namjae Jeon wrote:

quoted

The semantics of this flag are following:
1) It collapses the range lying between offset and length by removing
any data
   blocks which are present in this range and than updates all the
logical
   offsets of extents beyond "offset + len" to nullify the hole created
by
   removing blocks. In short, it does not leave a hole.
2) It should be used exclusively. No other fallocate flag in
combination.
3) Offset and length supplied to fallocate should be fs block size
aligned
   in case of xfs and ext4.
4) Collaspe range does not work beyond i_size.

What if the file is mmaped at the time somebody issues this command?
Seems to me we should drop pagecache pages that overlap with the
removed blocks.  If the removed range is not a multiple of PAGE_SIZE,
then we should also drop any pagecache pages after the removed range.

Hi Matthew.
Yes, right. So both xfs and ext4 call truncate_pagecache_range to drop
page caches before removing blocks.
truncate_pagecache_range(inode, offset, -1);
and end offset is -1, which mean all page cache will be dropped from
start offset to the end of file.

Oops, forgot to add "and if it is a multiple of page size, then we need
to update the offsets of any pages after the removed page".  We should
probably start easy though; just drop all pages that overlap the beginning
of the affected range to the end of the file.

Yes, right. current implementation does exactly as you pointed

 At some later point,
if there's demand, we can add the optimisation to adjust the offsets of
pages still in the cache.

-> Yes, Right. But if we consider that fs block size can be less than
page cache size,(512B, 1K, 2K)
I thought that it is proper to drop all pages from the start offset to
the end of the file.

Thanks for your reply.

--
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."

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