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e60f4e7082
Previously we'd avoided full extents in file data mapping items because we were deleting items from forest btrees directly. That created deletion items for every version of file extents as they were modified. Now we have the item cache which can remove deleted items from memory when deletion items aren't necessary. By layering file data extents on an extent layer, we can also transition allocators to use extents and fix a lot of problems in the radix block allocator. Most of this change is churn from changing allocator function and struct names. File data extents no longer have to manage loading and storing from and to packed extent items at a fixed granularity. All those loops are torn out and data operations now call the extent layer with their callbacks instead of calling its packed item extent functions. This now means that fallocate and especially restoring offline extents can use larger extents. Small file block allocation now comes from a cached extent which reduces item calls for small file data streaming writes. The big change in the server is to use more root structures to manage recursive modification instead of relying on the allocator to notice and do the right thing. The radix allocator tried to notice when it was actively operating on a root that it was also using to allocate and free metadata blocks. This resulted in a lot of bugs. Instead we now double buffer the server's avail and freed roots so that the server fills and drains the stable roots from the previous transaction. We also double buffer the core fs metadata avail root so that we can increase the time to reuse freed metadata blocks. The server now only moves free extents into client allocators when they fall below a low threshold. This reduces the shared modification of the client's allocator roots which requires cold block reads on both the client and server. Signed-off-by: Zach Brown <zab@versity.com>