At 06/03/2016 10:02 PM, Josef Bacik wrote:
On 06/01/2016 01:48 AM, Lu Fengqi wrote:
Only in the case of different root_id or different object_id,
check_shared
identified extent as the shared. However, If a extent was referred by
different offset of same file, it should also be identified as shared.
In addition, check_shared's loop scale is at least n^3, so if a extent
has too many references, even causes soft hang up.
First, add all delayed_ref to the ref_tree and calculate the unqiue_refs,
if the unique_refs is greater than one, return BACKREF_FOUND_SHARED.
Then individually add the on-disk reference(inline/keyed) to the
ref_tree
and calculate the unique_refs of the ref_tree to check if the unique_refs
is greater than one.Because once there are two references to return
SHARED, so the time complexity is close to the constant.
Reported-by: Tsutomu Itoh <t-i...@jp.fujitsu.com>
Signed-off-by: Lu Fengqi <lufq.f...@cn.fujitsu.com>
This is a lot of work for just wanting to know if something is shared.
Instead lets adjust this slightly. Instead of passing down a
root_objectid/inum and noticing this and returned shared, add a new way
to iterate refs. Currently we go gather all the refs and then do the
iterate dance, which is what takes so long. So instead add another
helper that calls the provided function every time it has a match, and
then we can pass in whatever context we want, and we return when
something matches. This way we don't have all this extra accounting,
and we're no longer passing root_objectid/inum around and testing for
some magic scenario. Thanks,
Josef
With this patch, we can quickly find extent that has more than one
reference(delayed, inline and keyed) and return SHARED immediately.
However, for indirect refs, we have to continue to resolve indirect refs
to their parent bytenr, and check if this parent bytenr is shared. So,
the original function is necessary. The original refs list reduces the
efficiency of search, so maybe we can use rb_tree to replace it for
optimize the original function in the furture. And, we just want to
solve the problem of check_shared now.
--
Thanks,
Lu
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