Increase the size of the buffer_head b_size field (only) for 64 bit platforms. Update some old and moldy comments in and around the structure as well. The b_size increase allows us to perform larger mappings and allocations for large I/O requests from userspace, which tie in with other changes allowing the get_block_t() interface to map multiple blocks at once.
Showing the changes to include/linux/buffer_head.h (1 of 4 files). Show all
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| @@ -46,25 +46,28 @@ struct address_space; · 45 unmodified lines | |||
| 46 | typedef void (bh_end_io_t)(struct buffer_head *bh, int uptodate); | 46 | typedef void (bh_end_io_t)(struct buffer_head *bh, int uptodate); |
| 47 | 47 | ||
| 48 | /* | 48 | /* |
| 49 | * Keep related fields in common cachelines. The most commonly accessed | 49 | * Historically, a buffer_head was used to map a single block |
| 50 | * field (b_state) goes at the start so the compiler does not generate | 50 | * within a page, and of course as the unit of I/O through the |
| 51 | * indexed addressing for it. | 51 | * filesystem and block layers. Nowadays the basic I/O unit |
| 52 | * is the bio, and buffer_heads are used for extracting block | ||
| 53 | * mappings (via a get_block_t call), for tracking state within | ||
| 54 | * a page (via a page_mapping) and for wrapping bio submission | ||
| 55 | * for backward compatibility reasons (e.g. submit_bh). | ||
| 52 | */ | 56 | */ |
| 53 | struct buffer_head { | 57 | struct buffer_head { |
| 54 | /* First cache line: */ | ||
| 55 | unsigned long b_state; /* buffer state bitmap (see above) */ | 58 | unsigned long b_state; /* buffer state bitmap (see above) */ |
| 56 | struct buffer_head *b_this_page;/* circular list of page's buffers */ | 59 | struct buffer_head *b_this_page;/* circular list of page's buffers */ |
| 57 | struct page *b_page; /* the page this bh is mapped to */ | 60 | struct page *b_page; /* the page this bh is mapped to */ |
| 58 | atomic_t b_count; /* users using this block */ | ||
| 59 | u32 b_size; /* block size */ | ||
| 60 | 61 | ||
| 61 | sector_t b_blocknr; /* block number */ | 62 | sector_t b_blocknr; /* start block number */ |
| 62 | char *b_data; /* pointer to data block */ | 63 | size_t b_size; /* size of mapping */ |
| 64 | char *b_data; /* pointer to data within the page */ | ||
| 63 | 65 | ||
| 64 | struct block_device *b_bdev; | 66 | struct block_device *b_bdev; |
| 65 | bh_end_io_t *b_end_io; /* I/O completion */ | 67 | bh_end_io_t *b_end_io; /* I/O completion */ |
| 66 | void *b_private; /* reserved for b_end_io */ | 68 | void *b_private; /* reserved for b_end_io */ |
| 67 | struct list_head b_assoc_buffers; /* associated with another mapping */ | 69 | struct list_head b_assoc_buffers; /* associated with another mapping */ |
| 70 | atomic_t b_count; /* users using this buffer_head */ | ||
| 68 | }; | 71 | }; |
| 69 | 72 | ||
| 70 | /* | 73 | /* |