hi!
please, look:
thread A commit thread
if (jh->b_committed_data) {
kfree(jh->b_committed_data);
jh->b_committed_data = NULL;
}
access for
b_committed_data == NULL ?
if (jh->b_frozen_data) {
jh->b_committed_data = jh->b_frozen_data;
jh->b_frozen_data = NULL;
}
or I miss something subtle here?
>>>>> Stephen C Tweedie (SCT) writes:
SCT> get_undo_access is a declaration of intention to modify the buffer.
SCT> When that happens, it calls do_get_write_access() with the force_copy
SCT> flag set. That means that it _always_ creates a new frozen_data copy of
SCT> the buffer the first time we get undo access to a bitmap buffer within
SCT> any given transaction. That basically means that for bitmaps,
SCT> frozen_data always holds the version of the buffer as of the end of the
SCT> previously completed transaction.
>> for_each_bh_in_forget_list() {
>> if (jh->b_committed_data) {
>> kfree(jh->b_committed_data);
jh-> b_committed_data = NULL;
>> }
SCT> Ah, but the *immediately* following lines are:
SCT> if (jh->b_frozen_data) {
jh-> b_committed_data = jh->b_frozen_data;
jh-> b_frozen_data = NULL;
SCT> }
SCT> so the frozen data that was preserved at get_undo_access() time has now
SCT> committed to disk and gets rotated into the b_committed_data version.
SCT> This is exactly how we get the new version of the committed data when
SCT> the old transaction commits.
SCT> Cheers,
SCT> Stephen
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This archive was generated by hypermail 2b29 : Fri May 23 2003 - 22:00:36 EST