| Title | Accounting overheads are too high on mark & sweep pools |
| Status | open |
| Priority | nice |
| Assigned user | Richard Brooksby |
| Organization | Ravenbrook |
| Description | Changelist 185888 introduced double-entry book-keeping to every segment in the LO, AWL, and AMS pool classes, resulting in a four word overhead on every segment. This is too high. |
| Analysis | 1. Define and justify "too high". 2. Each account in the segment takes up a whole 64-bit word, but the information it stores is usually only 9 bits long, though that depends on the size of the segment. Can it be compressed? 3. The accounts are redundant (being double-entry) but they're also double-entry at the level of the generation, so this may be excessive redundancy. 4. The accounts are only used for two things: to feed in to the generation accounts, and to speed up the allocation search. The allocation needs reform, and then perhaps they can be eliminated a the segment level. |
| How found | inspection |
| Evidence | LOSegStruct, AMSSegStruct, and AWLSegStruct |
| Created by | Richard Brooksby |
| Created on | 2016-04-29 08:54:37 |
| Last modified by | Gareth Rees |
| Last modified on | 2016-09-13 10:35:28 |
| History | 2016-04-29 RB Created. |