Add a new fiemap flag which forces the all of the extents in an inode to be cached in the extent_status tree. This is critically important when using AIO to a preallocated file, since if we need to read in blocks from the extent tree, the io_submit(2) system call becomes synchronous, and the AIO is no longer "A", which is bad. In addition, for most files which have an external leaf tree block, the cost of caching the information in the extent status tree will be less than caching the entire 4k block in the buffer cache. So it is generally a win to keep the extent information cached.
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| @@ -40,6 +40,7 @@ struct fiemap { · 39 unmodified lines | ||
| 40 | 40 | |
| 41 | 41 | #define FIEMAP_FLAG_SYNC 0x00000001 /* sync file data before map */ |
| 42 | 42 | #define FIEMAP_FLAG_XATTR 0x00000002 /* map extended attribute tree */ |
| 43 | +#define FIEMAP_FLAG_CACHE 0x00000004 /* request caching of the extents */ | |
| 43 | 44 | |
| 44 | 45 | #define FIEMAP_FLAGS_COMPAT (FIEMAP_FLAG_SYNC | FIEMAP_FLAG_XATTR) |
| 45 | 46 | |