>>>>> Werner Almesberger (WA) writes: WA> Do you plan to reserve space as "blocks, somewhere", or as "these WA> specific on-disk locations" ? In ABISS, we did something of the WA> latter kind (in order to make large contiguous allocations also on WA> FAT), and it turned out to be a big mess, because ABISS needed too WA> much support from the file system driver. So we just scrapped that WA> bit :-)
I see no reason to reserve specific block in ->prepare/->commit in delayed allocation case. We already do this with reservation. The sole point of delayed allocation is to allocate many blocks at once: to minimize fragmentation, to decrease allocator involvement, to avoid allocation at all if the file gets truncated quickly. WA> The main parts: we added a new page flag, PG_delalloc, which WA> basically tells everyone to stay away from that page. There are WA> two purposes: (a) to make sure no allocation happens unless WA> explicitly requested, and (b) prevent the page from being written WA> back while it is still in ABISS' playout buffer. The reason for WA> (b) is that the page gets locked during writeback, which could WA> cause delays if the ABISS-using application then decides to WA> access the page. locked during writeback? PG_writeback should be used instead of PG_locked. thanks, Alex - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
