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Semi-ready patch, see ToDo


VFS part

In write path, VFS's function __block_write_full_page() is called with special get_block() method which doesn't allocate block immediately, but reserve it only and mark bh Delay.

In flush path, VFS's function mpage_da_writepages() scans mapping for dirty pages, collects dirty non-allocated bhs, tries to allocate them with minimal calls to get_block() method, applies allocated blocks to delayed bhs and drops Delay state.research papers

ext4 part

ext4 implements two different get_block() methods:

  • one for write(2) path
* checks whether block is already allocated
* if it's not, then reserves block(s) needed for data and metadata and mark bh Delay
  • another one for flush path
* starts transaction
* allocates blocks
* updates on-disk size
* closes transaction


  • integrate reservation
  • data=ordered
  • quota
  • bmap
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