Hi Vyacheslav, > So, as a result, when you are talking about logical block placement > then it doesn't mean that you are talking about writes in few physical > erase blocks. Because only mapping table of FTL knows what physical > erase blocks are changed really. ntly). For powerful FTL/controllers it almost doesn't make a difference whether you write in-place or in the "almost random" style you propose. Those FTLs usually have a fully associative fine-grained physical-to-logical mapping, so they also can distribute the wear evenly across the entire NAND. However there are also FTLs (SD cards, managed NAND, ...) arround which do only mapping on erase-block level, with limited associativity - often lacking a random write unit. So each logical block is mapped to one of n possible physical erase blocks (for SD cards 4MB erase blocks are quite common) and for each single write a full erase block has to be erased. And as there are only n physcial blocks which can be mapped to this logical block, the card pretty soon starts to develop bad sectors (even worse, these days often cheap TLC flash is used limited to < 500 erase cycles). The linaro guys did a survey on this some time ago: https://wiki.linaro.org/WorkingGroups/KernelArchived/Projects/FlashCardSurvey Very interesting is the paragraph about "Access modes", there are still a lot of controllers which don't feature a random write unit. > We know about clean (or unclean) umount from the superblock. > So, you should update superblock for keeping such knowledge. > Otherwise, you will need to perform linear scan always. > I don't quite follow your thought. If we will not update superblock then > how we can save any changes in superblock? Only update the superblock at mount/unmount time, and do a linear scan in the case of an unclean shutdown. Thanks, Clemens -- To unsubscribe from this list: send the line "unsubscribe linux-nilfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
