Documentation/filesystems/xfs-delayed-logging-design.rst

465 vector array that points to the changed regions in the item. The log write code
469 allocated memory buffer big enough to fit the formatted vector.
471 If we then copy the vector into the memory buffer and rewrite the vector to
476 resulting in a vector that is transactionally consistent and can be accessed
484 Current format log vector::
495 Delayed logging vector::
509 The memory buffer and associated vector need to be passed as a single object,
514 The reason for keeping the vector around after we've formatted the memory
516 If we don't keep the vector around, we do not know where the region boundaries
523 Hence we need to keep the vector, but by attaching the memory buffer to it and
524 rewriting the vector addresses to point at the memory buffer we end up with a
537 log item is the natural place to store this vector and buffer, and also makes sense
631 buffer and log vector attached to each log item needs to be attached to the
638 	Log Item <-> log vector 1	-> memory buffer
639 	   |				-> vector array
641 	Log Item <-> log vector 2	-> memory buffer
642 	   |				-> vector array
647 	Log Item <-> log vector N-1	-> memory buffer
648 	   |				-> vector array
650 	Log Item <-> log vector N	-> memory buffer
651 					-> vector array
654 vector list would look like::
659 	log vector 1	-> memory buffer
660 	   |		-> vector array
663 	log vector 2	-> memory buffer
664 	   |		-> vector array
670 	log vector N-1	-> memory buffer
671 	   |		-> vector array
674 	log vector N	-> memory buffer
675 			-> vector array
679 start, while the checkpoint flush code works over the log vector chain to
686 and unpin) in the log vector chain and then free the log vector chain and
692 vectors and break the link between the log item and the log vector means that
694 the log vector chaining. If we track by the log vectors, then we only need to
695 break the link between the log item and the log vector, which means we should
772 number of split log vector regions are going to be used. We can track the
789 vector is 12 bytes, so the total to be logged is approximately 1.75MB. In
1040 		Format item into log vector + buffer
1041 		Attach log vector and buffer to log item