btrfs core patches for direct I/O

As if a Monday after a long holiday was not bad enough... this series has some simple patches in existing btrfs code that I want to make for btrfs directio code.

The RESEND patches 1-5 were sent to Chris in December because IMO they have value without my directio code. You need them to apply some of the subsequent patches.

IMO patch 6 is also of value independent of direct I/O, it reduces vmalloc use by 42K per worker, though we still use 268K per worker (ouch).

Patches 7 - 12 don't have value without direct I/O. I'm sending them RFC as they can be understood by themselves, and they are much simpler than the directio code that uses them. :)

Note - might as well explain this now as later when I send the big mess of dio.c for review. The existing core code for pagecache doesn't work for directio because the existing I/O routines depend on peeking inside a struct page to get the valid btrfs inode info. Sorry, no can do, we don't own that page. And rewriting the whole pagecache I/O stack to eliminate dependence on struct page would be too scary IMO.

FWIW, fsx didn't crash on this series.

jim

That would simply need another passed argument in a few strategic places, won't it? I can't imagine it would need a full "rewrite"

-Andi

[email protected] -- Speaking for myself only.

I should not have said "rewrite", it is the wrong word, and yes some changes in some places would be easy.

jim