diff options
Diffstat (limited to 'Documentation/block/biodoc.txt')
-rw-r--r-- | Documentation/block/biodoc.txt | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt index 34bf8f60d8f8..c6c9a9c10d7f 100644 --- a/Documentation/block/biodoc.txt +++ b/Documentation/block/biodoc.txt | |||
@@ -183,7 +183,7 @@ it, the pci dma mapping routines and associated data structures have now been | |||
183 | modified to accomplish a direct page -> bus translation, without requiring | 183 | modified to accomplish a direct page -> bus translation, without requiring |
184 | a virtual address mapping (unlike the earlier scheme of virtual address | 184 | a virtual address mapping (unlike the earlier scheme of virtual address |
185 | -> bus translation). So this works uniformly for high-memory pages (which | 185 | -> bus translation). So this works uniformly for high-memory pages (which |
186 | do not have a correponding kernel virtual address space mapping) and | 186 | do not have a corresponding kernel virtual address space mapping) and |
187 | low-memory pages. | 187 | low-memory pages. |
188 | 188 | ||
189 | Note: Please refer to DMA-mapping.txt for a discussion on PCI high mem DMA | 189 | Note: Please refer to DMA-mapping.txt for a discussion on PCI high mem DMA |
@@ -391,7 +391,7 @@ forced such requests to be broken up into small chunks before being passed | |||
391 | on to the generic block layer, only to be merged by the i/o scheduler | 391 | on to the generic block layer, only to be merged by the i/o scheduler |
392 | when the underlying device was capable of handling the i/o in one shot. | 392 | when the underlying device was capable of handling the i/o in one shot. |
393 | Also, using the buffer head as an i/o structure for i/os that didn't originate | 393 | Also, using the buffer head as an i/o structure for i/os that didn't originate |
394 | from the buffer cache unecessarily added to the weight of the descriptors | 394 | from the buffer cache unnecessarily added to the weight of the descriptors |
395 | which were generated for each such chunk. | 395 | which were generated for each such chunk. |
396 | 396 | ||
397 | The following were some of the goals and expectations considered in the | 397 | The following were some of the goals and expectations considered in the |
@@ -403,14 +403,14 @@ i. Should be appropriate as a descriptor for both raw and buffered i/o - | |||
403 | for raw i/o. | 403 | for raw i/o. |
404 | ii. Ability to represent high-memory buffers (which do not have a virtual | 404 | ii. Ability to represent high-memory buffers (which do not have a virtual |
405 | address mapping in kernel address space). | 405 | address mapping in kernel address space). |
406 | iii.Ability to represent large i/os w/o unecessarily breaking them up (i.e | 406 | iii.Ability to represent large i/os w/o unnecessarily breaking them up (i.e |
407 | greater than PAGE_SIZE chunks in one shot) | 407 | greater than PAGE_SIZE chunks in one shot) |
408 | iv. At the same time, ability to retain independent identity of i/os from | 408 | iv. At the same time, ability to retain independent identity of i/os from |
409 | different sources or i/o units requiring individual completion (e.g. for | 409 | different sources or i/o units requiring individual completion (e.g. for |
410 | latency reasons) | 410 | latency reasons) |
411 | v. Ability to represent an i/o involving multiple physical memory segments | 411 | v. Ability to represent an i/o involving multiple physical memory segments |
412 | (including non-page aligned page fragments, as specified via readv/writev) | 412 | (including non-page aligned page fragments, as specified via readv/writev) |
413 | without unecessarily breaking it up, if the underlying device is capable of | 413 | without unnecessarily breaking it up, if the underlying device is capable of |
414 | handling it. | 414 | handling it. |
415 | vi. Preferably should be based on a memory descriptor structure that can be | 415 | vi. Preferably should be based on a memory descriptor structure that can be |
416 | passed around different types of subsystems or layers, maybe even | 416 | passed around different types of subsystems or layers, maybe even |
@@ -1013,7 +1013,7 @@ Characteristics: | |||
1013 | i. Binary tree | 1013 | i. Binary tree |
1014 | AS and deadline i/o schedulers use red black binary trees for disk position | 1014 | AS and deadline i/o schedulers use red black binary trees for disk position |
1015 | sorting and searching, and a fifo linked list for time-based searching. This | 1015 | sorting and searching, and a fifo linked list for time-based searching. This |
1016 | gives good scalability and good availablility of information. Requests are | 1016 | gives good scalability and good availability of information. Requests are |
1017 | almost always dispatched in disk sort order, so a cache is kept of the next | 1017 | almost always dispatched in disk sort order, so a cache is kept of the next |
1018 | request in sort order to prevent binary tree lookups. | 1018 | request in sort order to prevent binary tree lookups. |
1019 | 1019 | ||