Hi, lister:
I use ceph’version 10.2.0
Analysis FileJournal::prepare_entry，when prepare journal bufferlist，it’s divided into 5 parts：head pre_pad data post_pad head
Then reuild for buffer list to 4K align。rebuild_aligned remalloc 4K aligned memory。（each 4K aligned memory is as small as possible）
Detailed code：
FileJournal::prepare_entry(vector<ObjectStore::Transaction>& tls, bufferlist* tbl)
Encode for transaction ::encode(*p, bl);
ebl.append((const char*)&h, sizeof(h));
ebl.push_back(buffer::create_static(h.pre_pad, zero_buf));
ebl.claim_append(bl, buffer::list::CLAIM_ALLOW_NONSHAREABLE); // potential zero-copy
ebl.push_back(buffer::create_static(h.post_pad, zero_buf));
ebl.append((const char*)&h, sizeof(h));
ret = ebl.rebuild_aligned(CEPH_DIRECTIO_ALIGNMENT);
question:
before rebuild_aligned，as many ptr is aligned as 4K，so you can apply less memory.is it?
head 40 pre_pad 2736 bl 4196233 post_pad 3447 tail 40 total:4K*1026
rebuild_aligned will remalloc memory 4K*1026, all need rebuild
Detail log info:
In code, this log message caught my attention，the log information of these 5 valuse is not expected.
dout(10) << " len " << bl.length() << " -> " << size << " (head " << head_size << " pre_pad " << h.pre_pad
<< " bl " << bl.length() << " post_pad " << post_pad << " tail " << head_size << ")"
<< " (bl alignment " << data_align << ")" << dendl;
2017-10-17 19:50:28.721922 7f21d73fe700 10 journal len 4196233 -> 4202496 (head 40 pre_pad 2736 bl 4196233 post_pad 3447 tail 40) (bl alignment 2776)
2017-10-17 19:50:28.873261 7f21ccfff700 10 journal len 4196131 -> 4202496 (head 40 pre_pad 4046 bl 4196131 post_pad 2239 tail 40) (bl alignment 4086)
2017-10-17 19:50:28.897520 7f21d43ff700 10 journal len 4196131 -> 4202496 (head 40 pre_pad 4046 bl 4196131 post_pad 2239 tail 40) (bl alignment 4086)
2017-10-17 19:50:28.974811 7f21cf800700 10 journal len 4196131 -> 4202496 (head 40 pre_pad 4046 bl 4196131 post_pad 2239 tail 40) (bl alignment 4086)
2017-10-17 19:50:29.013940 7f21ccfff700 10 journal len 4196215 -> 4202496 (head 40 pre_pad 2754 bl 4196215 post_pad 3447 tail 40) (bl alignment 2794)
2017-10-17 19:50:29.292165 7f21ce3ff700 10 journal len 4196215 -> 4202496 (head 40 pre_pad 2754 bl 4196215 post_pad 3447 tail 40) (bl alignment 2794)
2017-10-17 19:50:29.311296 7f21cf800700 10 journal len 4196233 -> 4202496 (head 40 pre_pad 2736 bl 4196233 post_pad 3447 tail 40) (bl alignment 2776)
2017-10-17 19:50:29.416240 7f21d43ff700 10 journal len 4196215 -> 4202496 (head 40 pre_pad 2754 bl 4196215 post_pad 3447 tail 40) (bl alignment 2794)
2017-10-17 19:50:30.111561 7f21cc7fe700 10 journal len 4196131 -> 4202496 (head 40 pre_pad 4046 bl 4196131 post_pad 2239 tail 40) (bl alignment 4086)
2017-10-17 19:50:30.444729 7f21d23ff700 10 journal len 4196131 -> 4202496 (head 40 pre_pad 4046 bl 4196131 post_pad 2239 tail 40) (bl alignment 4086)
2017-10-17 19:50:30.448686 7f21ccfff700 10 journal len 4196233 -> 4202496 (head 40 pre_pad 2736 bl 4196233 post_pad 3447 tail 40) (bl alignment 2776)
2017-10-17 19:50:30.559626 7f21d43ff700 10 journal len 4196131 -> 4202496 (head 40 pre_pad 4046 bl 4196131 post_pad 2239 tail 40) (bl alignment 4086)
2017-10-17 19:50:30.592541 7f21d63fe700 10 journal len 4196233 -> 4202496 (head 40 pre_pad 2736 bl 4196233 post_pad 3447 tail 40) (bl alignment 2776)
2017-10-17 19:50:30.599527 7f21cb7ff700 10 journal len 4196215 -> 4202496 (head 40 pre_pad 2754 bl 4196215 post_pad 3447 tail 40) (bl alignment 2794)
2017-10-17 19:50:30.613123 7f21d13ff700 10 journal len 4196131 -> 4202496 (head 40 pre_pad 4046 bl 4196131 post_pad 2239 tail 40) (bl alignment 4086)
��.n��������+%������w��{.n����z��u���ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
