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"overkill "}, + :properties {:color "green"}} + {:id #uuid "643a8ef8-7d3f-4794-9f00-4973a3be9bb7", + :page 527, + :position {:bounding {:x1 652.65625, + :y1 1170.484375, + :x2 750.930908203125, + :y2 1195.484375, + :width 921.6, + :height 1382.4}, + :rects ({:x1 652.65625, + :y1 1170.484375, + :x2 750.930908203125, + :y2 1195.484375, + :width 921.6, + :height 1382.4}), + :page 527}, + :content {:text "data region"}, + :properties {:color "yellow"}} + {:id #uuid "643a8f4b-ac22-4cb8-b68d-e7f3078709c1", + :page 528, + :position {:bounding {:x1 578.015625, + :y1 575.359375, + :x2 676.2728271484375, + :y2 600.359375, + :width 921.6, + :height 1382.4}, + :rects ({:x1 578.015625, + :y1 575.359375, + :x2 676.2728271484375, + :y2 600.359375, + :width 921.6, + :height 1382.4}), + :page 528}, + :content {:text "inode table"}, + :properties {:color "yellow"}} + {:id #uuid "643a8fa4-9783-4e86-8b04-2fad1f3a5c66", + :page 528, + :position {:bounding {:x1 400.796875, + :y1 1042.890625, + :x2 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1045.078125, + :width 921.6, + :height 1382.4}), + :page 529}, + :content {:text " Inode"}, + :properties {:color "yellow"}} + {:id #uuid "643a93f0-e122-4ea5-a228-48607f93e404", + :page 531, + :position {:bounding {:x1 183.359375, + :y1 908.28125, + :x2 402.9515380859375, + :y2 936.28125, + :width 921.6, + :height 1382.4}, + :rects ({:x1 183.359375, + :y1 908.28125, + :x2 402.9515380859375, + :y2 936.28125, + :width 921.6, + :height 1382.4}), + :page 531}, + :content {:text "The Multi-Level Index"}, + :properties {:color "yellow"}} + {:id #uuid "643a950d-c2c2-419b-8206-0b957b7de178", + :page 531, + :position {:bounding {:x1 0, + :y1 589, + :x2 797.5996704101562, + :y2 1110.25, + :width 921.6, + :height 1382.4}, + :rects ({:x1 0, + :y1 589, + :x2 0, + :y2 611, + :width 921.6, + :height 1382.4} + {:x1 0, + :y1 605, + :x2 0, + :y2 627, + :width 921.6, + :height 1382.4} + {:x1 0, + :y1 621, + :x2 0, + :y2 643, + :width 921.6, + :height 1382.4} + {:x1 420.269775390625, + :y1 1027.484375, + 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Thus, an inode may have some fixed number of direct pointers (e.g., 12), and a single indirect pointer. If a file grows large enough, an indirect block is allocated (from the data-block region of the disk), and the inode’s slot for an indirect pointer is set to point to it."}, + :properties {:color "yellow"}} + {:id #uuid "643a96a0-f55d-4a84-bf93-4732a282b124", + :page 532, + :position {:bounding {:x1 571.3375854492188, + :y1 998.0625, + :x2 615.238037109375, + :y2 1017.0625, + :width 921.6, + :height 1382.4}, + :rects ({:x1 571.3375854492188, + :y1 998.0625, + :x2 615.238037109375, + :y2 1017.0625, + :width 921.6, + :height 1382.4}), + :page 532}, + :content {:text "akin "}, + :properties {:color "green"}} + {:id #uuid "643a96cb-bb7d-44c7-ac86-1e55a7ea3249", + :page 533, + :position {:bounding {:x1 413.6831359863281, + :y1 544.78125, + :x2 481.9478759765625, + :y2 563.78125, + :width 921.6, + :height 1382.4}, + :rects ({:x1 413.6831359863281, + :y1 544.78125, + :x2 481.9478759765625, + :y2 563.78125, + :width 921.6, + :height 1382.4}), + :page 533}, + :content {:text "readily "}, + :properties {:color "green"}} + {:id #uuid "643a96d1-5114-40f7-9dad-4291462344ff", + :page 533, + :position {:bounding {:x1 280.546875, + :y1 376.59375, + :x2 700.4242553710938, + :y2 401.59375, + :width 921.6, + :height 1382.4}, + :rects ({:x1 384.265625, + :y1 376.59375, + :x2 700.4242553710938, + :y2 401.59375, + :width 921.6, + :height 1382.4} + {:x1 280.546875, + :y1 378.3125, + :x2 387.875, + :y2 397.4375, + :width 921.6, + :height 1382.4}), + :page 533}, + :content {:text "Figure 40.2: File System Measurement Summary"}, + :properties {:color "yellow"}} + {:id #uuid "643a975d-f0a2-47e7-bf85-63a300a2c504", + :page 532, + :position {:bounding {:x1 373.015625, + :y1 208.015625, + :x2 624.874267578125, + :y2 227.140625, + :width 921.6, + :height 1382.4}, + :rects ({:x1 373.015625, + :y1 208.015625, + :x2 624.874267578125, + :y2 227.140625, + :width 921.6, + :height 1382.4}), + :page 532}, + :content {:text "EXTENT-BASED APPROACHES"}, + :properties {:color "yellow"}} + {:id #uuid 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Second, it places all files that are in the same directory in the cylinder group of the directory they are in. 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:extra {:page 507}} + :extra {:page 558}} diff --git a/journals/2023_04_14.md b/journals/2023_04_14.md new file mode 100644 index 0000000..877f270 --- /dev/null +++ b/journals/2023_04_14.md @@ -0,0 +1 @@ +- 终于把排名开下来了。 \ No newline at end of file diff --git a/journals/2023_04_15.md b/journals/2023_04_15.md new file mode 100644 index 0000000..3d79c0d --- /dev/null +++ b/journals/2023_04_15.md @@ -0,0 +1 @@ +- 英文版简历绝赞制作中 \ No newline at end of file diff --git a/logseq/bak/logseq/config/2023-04-13T15_47_53.912Z.Desktop.edn b/logseq/bak/logseq/config/2023-04-15T15_41_51.461Z.Desktop.edn similarity index 99% rename from logseq/bak/logseq/config/2023-04-13T15_47_53.912Z.Desktop.edn rename to logseq/bak/logseq/config/2023-04-15T15_41_51.461Z.Desktop.edn index dec5a7c..10c46a7 100644 --- a/logseq/bak/logseq/config/2023-04-13T15_47_53.912Z.Desktop.edn +++ b/logseq/bak/logseq/config/2023-04-15T15_41_51.461Z.Desktop.edn @@ -343,6 +343,7 @@ ;; ;use Percent-encoding for other invalid characters :file/name-format :triple-lowbar :ui/show-brackets? false + :feature/enable-timetracking? false ;; specify the format of the filename for journal files ;; :journal/file-name-format "yyyy_MM_dd" diff --git a/logseq/bak/logseq/config/2023-04-13T11_23_48.892Z.Desktop.edn b/logseq/bak/logseq/config/2023-04-15T15_42_07.581Z.Desktop.edn similarity index 99% rename from logseq/bak/logseq/config/2023-04-13T11_23_48.892Z.Desktop.edn rename to logseq/bak/logseq/config/2023-04-15T15_42_07.581Z.Desktop.edn index f69d742..657d2d7 100644 --- a/logseq/bak/logseq/config/2023-04-13T11_23_48.892Z.Desktop.edn +++ b/logseq/bak/logseq/config/2023-04-15T15_42_07.581Z.Desktop.edn @@ -343,6 +343,7 @@ ;; ;use Percent-encoding for other invalid characters :file/name-format :triple-lowbar :ui/show-brackets? true + :feature/enable-timetracking? false ;; specify the format of the filename for journal files ;; :journal/file-name-format "yyyy_MM_dd" diff --git a/pages/hls__ostep_1681115599584_0.md b/pages/hls__ostep_1681115599584_0.md index 184ae20..25a1189 100644 --- a/pages/hls__ostep_1681115599584_0.md +++ b/pages/hls__ostep_1681115599584_0.md @@ -1165,44 +1165,387 @@ file-path:: ../assets/ostep_1681115599584_0.pdf ls-type:: annotation id:: 64382ab8-ad41-4c20-be74-3ce7446f20d6 hl-color:: green -- Files And Directories +- ## Files And Directories ls-type:: annotation hl-page:: 498 hl-color:: yellow id:: 6438d8bf-19fd-4a4a-b491-3887c425aebf + collapsed:: true - File Directory - File: a linear array of bytes, each of which can be read or written - Directory: a list of *(user-readable name, low-level name)* pairs - directory tree, root directory, separator, sub-directories, absolute pathname - inode number: low-level name of a file or directory - - Creating Files: system call `open` with `O_CREAT` flag - hl-page:: 500 - ls-type:: annotation - id:: 6438dd4b-55ba-4649-90fd-7de69ed9c2ba - hl-color:: yellow - - file descriptor: an integer, ==private per process==, used to access files - hl-page:: 501 + - File operations + - Creating Files: system call `open` with `O_CREAT` flag + hl-page:: 500 ls-type:: annotation - id:: 6438dd78-68fe-47c6-8ca6-b2de3206f4f1 + id:: 6438dd4b-55ba-4649-90fd-7de69ed9c2ba hl-color:: yellow - - can be seen as a handle for file operations, or a pointer to an object of type file - - Reading And Writing Files: system call `read` and `write` - hl-page:: 502 - ls-type:: annotation - id:: 6438e073-2636-4ec8-807d-3ecf83a5c0c0 - hl-color:: yellow - - Non-sequential access: system call `lseek(fd, offset, whence)` - - explicit and implicit update to file offset - - open file table: represent all currently opened files in the system - - Shared File Table Entries - ls-type:: annotation - hl-page:: 506 - hl-color:: yellow - id:: 6438e88b-e3e6-44a4-9f79-411c1f27ae71 - - On every `open` call, the OS creates a new entry in the *open file table* even for the same file (same inode). Thus, they have independent offsets. - - Through `fork` or `dup`, we can make 2 file descriptors point to the same entry. In this case, reference count is needed to track when to release the entry. - - Figure 39.3: Processes Sharing An Open File Table Entry + - file descriptor: an integer, ==private per process==, used to access files + hl-page:: 501 ls-type:: annotation - hl-page:: 508 + id:: 6438dd78-68fe-47c6-8ca6-b2de3206f4f1 hl-color:: yellow - id:: 6438e98b-b46f-4038-a984-eb172a628cc7 \ No newline at end of file + - can be seen as a handle for file operations, or a pointer to an object of type file + - Reading And Writing Files: system call `read` and `write` + hl-page:: 502 + ls-type:: annotation + id:: 6438e073-2636-4ec8-807d-3ecf83a5c0c0 + hl-color:: yellow + - Non-sequential access: system call `lseek(fd, offset, whence)` + - explicit and implicit update to file offset + - open file table: represent all currently opened files in the system + - Shared File Table Entries + ls-type:: annotation + hl-page:: 506 + hl-color:: yellow + id:: 6438e88b-e3e6-44a4-9f79-411c1f27ae71 + - On every `open` call, the OS creates a new entry in the *open file table* even for the same file (same inode). Thus, they have ==independent offsets==. + - Through `fork` or `dup`, we can make 2 file descriptors point to the ==same entry==. In this case, ==reference count== is needed to track when to release the entry. + - Figure 39.3: Processes Sharing An Open File Table Entry + ls-type:: annotation + hl-page:: 508 + hl-color:: yellow + id:: 6438e98b-b46f-4038-a984-eb172a628cc7 + - Writing Immediately + ls-type:: annotation + hl-page:: 509 + hl-color:: yellow + id:: 643a7463-39e5-4645-8b43-b8be7b8ea7bc + - `write` system call is generally buffered, so the change may be applied to the disk some time later + - In rare cases, this could lead to data loss which is unacceptable for software like DB.j + - `fsync()` a particular file descriptor, and then the FS will force all dirty data to disk. + - In some cases, `fsync` the directory containing the target file is also necessary. + id:: 643a7594-e799-4dec-a9f6-fa94fada363f + - Renaming File: A special system call `rename(char*, char*)` for this, which is usually implemented to be atomic. + hl-page:: 509 + ls-type:: annotation + id:: 643a782a-b874-4f34-9968-50b69a04b849 + hl-color:: yellow + - File Information: `stat` or `fstat` system call which fetches information store in the file's *inode* + hl-page:: 510 + ls-type:: annotation + id:: 643a789e-6346-4845-9d38-95d26927a32b + hl-color:: yellow + - Removing Files: `unlink` + hl-page:: 511 + ls-type:: annotation + id:: 643a79be-d297-4f8d-8825-83c9f830af0e + hl-color:: yellow + - Directory Operations + - Making Directories: `mkdir`. Even an empty (newly created) directory has 2 entries: `.` and `..` + hl-page:: 512 + ls-type:: annotation + id:: 643a7a52-0c85-435c-8250-3f4198a09fc0 + hl-color:: yellow + - Reading Directories: 3 calls `opendir` `readdir` `closedir` and a `dirent` structure with a few fields. A directory "file" is comprised of many entries said above. + hl-page:: 513 + ls-type:: annotation + id:: 643a7c32-0be4-4a2e-9532-31869f4e725a + hl-color:: yellow + - Deleting Directories: `rmdir`. Note that, this syscall can only remove empty directories or it will simply fail. + hl-page:: 514 + ls-type:: annotation + id:: 643a7d55-768c-4881-b78d-f721c8d7929d + hl-color:: yellow + - Links + - Hard Links + hl-page:: 514 + ls-type:: annotation + id:: 643a7d87-b945-4068-94dd-2b2d203eae67 + hl-color:: yellow + - syscall `link` creates another name in the directory which refers to ==the same inode== of the original file. + - The *inode* keeps a reference count indicating how many hard links refer to it. On each `unlink`, RC decreases and the file will be deleted once the RC gets to 0. + - Hard links are essentially ==entries in directories== and hard links pointing to the same *inode* are just ==identical except their names==. + - An interesting usage of `link` is to rename, link to new and unlink the old + - Limitation: cannot link to a directory, cannot link to file on another partition (because *inode numbers* are only unique in the same FS/partition) + - Symbolic Links (Soft Links) + hl-page:: 516 + ls-type:: annotation + id:: 643a8017-1499-4cd3-a015-0f1e8d143e93 + hl-color:: yellow + - syscall `symlink` + - A symbolic link is essentially a ==special type of file==, which holds the pathname of the linked-to file. + - Dangling reference is possible, when then original file is deleted. + - Permission Bits + ls-type:: annotation + hl-page:: 518 + hl-color:: yellow + id:: 643a84cb-102e-4beb-a138-e8690f68356f + - 10 characters (as shown in the out of `ls`) + - The left most indicates the type of the file, such as `-` for regular, `d` for directory, `s` for symbolic link and so on. + - The other characters are grouped by 3, each corresponding to a bit. Each 3-bit group indicates the permission of *owner*, *group* and *anyone*, and the bits means namely r/w/x. Note that as for directories, x bit represents the permission to enter directory. +- eponymous (与标题)同名的 + hl-page:: 512 + ls-type:: annotation + id:: 643a7a83-66d0-4bbc-8b17-bd7604a0ed5f + hl-color:: green +- hamster 仓鼠 + hl-page:: 515 + ls-type:: annotation + id:: 643a7dda-5c26-4ed5-8e06-c03e5a0e9fb7 + hl-color:: green +- ## File System Implementation + hl-page:: 526 + ls-type:: annotation + id:: 643a88bf-206b-4b6d-9d92-95516bcbe270 + hl-color:: yellow + collapsed:: true + - The Mental Model: data structure of the FS and its access methods + hl-page:: 526 + ls-type:: annotation + id:: 643a8c8e-b3ae-4de8-9280-75201b02d6db + hl-color:: yellow + - Disk Organization + - **blocks**: divide the disk into blocks (i.e. commonly used 4KB) + hl-page:: 527 + ls-type:: annotation + id:: 643a8ce0-15b0-4d37-987d-6e649a59b616 + hl-color:: yellow + - **data region**: most of the space is user data + hl-page:: 527 + ls-type:: annotation + id:: 643a8ef8-7d3f-4794-9f00-4973a3be9bb7 + hl-color:: yellow + - **inode table**: an array of inodes containing metadata to track per-file information + hl-page:: 528 + ls-type:: annotation + id:: 643a8f4b-ac22-4cb8-b68d-e7f3078709c1 + hl-color:: yellow + - **allocation structures**: recording information about free blocks, such as free list or bitmap. The `vsfs` from the book has one for inodes and another one for user data. + hl-page:: 528 + ls-type:: annotation + id:: 643a8fa4-9783-4e86-8b04-2fad1f3a5c66 + hl-color:: yellow + - **superblock**: information about the whole file system + hl-page:: 529 + ls-type:: annotation + id:: 643a9022-da94-4092-8a64-e22cd2364365 + hl-color:: yellow + - Inode + ls-type:: annotation + hl-page:: 529 + hl-color:: yellow + id:: 643a92a1-90df-4342-a183-85c55242b8af + - **i-number**: each inode is referred to by a number (low-level name). Given an i-number, the on-disk location of the inode could be calculated fairly easily. Note that disk is not byte-addressed, need to read the whole sector. + - **metadata**: Inside each inode is virtually all of the information you need about a file. In addition, some necessary data for looking up data blocks. + - The Multi-Level Index + ls-type:: annotation + hl-page:: 531 + hl-color:: yellow + id:: 643a93f0-e122-4ea5-a228-48607f93e404 + - **direct pointer**: refer to one disk block that belongs to the file + - **indirect pointer**: points to a ==block that contains more pointers==, each pointing to a user data block. + - An inode may have s==ome fixed number of direct pointers==, and ==a single indirect pointer==. If a file grows large enough, an indirect block is allocated (from the ==data-block region of the disk==), and the inode’s slot for an indirect pointer is set to point to it. If even file grows even larger, add double/triple/... indirect pointer to your inode. The pointer refers to a ==block containing pointers to indirect blocks==, described above. + hl-page:: 531 + ls-type:: annotation + id:: 643a950d-c2c2-419b-8206-0b957b7de178 + hl-color:: yellow + - Figure 40.2: File System Measurement Summary -- Most files are small + hl-page:: 533 + ls-type:: annotation + id:: 643a96d1-5114-40f7-9dad-4291462344ff + hl-color:: yellow + - Extent-based approaches + hl-page:: 532 + ls-type:: annotation + id:: 643a975d-f0a2-47e7-bf85-63a300a2c504 + hl-color:: yellow + - **extent**: a disk pointer and a length (how many contiguous blocks are there starting from the pointer) + - The advantage of this kind of approach is that, it is more compact, thus ==saving a lot of metadata==. The disadvantage is that, sometimes it is not easy to find many ==contiguous chunks==. Thus it works better when there is enough free space. + id:: 643a97ff-4b62-41bf-aa72-7316a8f3b974 + - Linked-based approaches (FAT) + hl-page:: 534 + ls-type:: annotation + id:: 643a9c2b-a519-4800-9188-253b13e9c2e5 + hl-color:: yellow + - For each file, there is only one ==pointer to the first block== of the file. If more blocks are needed, add a ==pointer to another block at the end of this block==. + - Directory Organization + ls-type:: annotation + hl-page:: 533 + hl-color:: yellow + id:: 643a990d-2b82-4bed-a49d-46746821b5a4 + - A linear ==array of entries==. Each entry is a`(entry name, inode number)` pair, and perhaps an additional `length` (total bytes of this entry) and `strlen` (for the name). + - Directory, from the FS's perspective, is a ==special type of file==. Directories are allocated in *data region*, and also has corresponding inodes. + - Deleting a file can leave an empty space in the middle of the directory's block, and thus the FS needs to handle that (maybe mark it for reuse?). + - Free Space Management + ls-type:: annotation + hl-page:: 535 + hl-color:: yellow + id:: 643a9d3c-3847-4a2e-b50e-f8423b089b39 + - For our simple `vsfs`, search through the bitmap. + - pre-allocation: when allocating, look for a sequence of blocks (contiguous on disk) and give them to the new file, in order to improve performance + hl-page:: 535 + ls-type:: annotation + id:: 643a9d6e-eab7-475c-9822-9b2efa21e6f0 + hl-color:: yellow + - Reading A File From Disk + ls-type:: annotation + hl-page:: 536 + hl-color:: yellow + id:: 643a9e6c-c2bd-48b9-80b8-b98340f91f7a + - Open: traverse the pathname and locate the desired inode. Since the inode of root directory `/` is fixed, we can start from `/`: load inode, read directory data, search for the next-level entry and recursively go down until the desired file's inode is loaded. + hl-page:: 536 + ls-type:: annotation + id:: 643a9e8a-5f34-4dc9-817b-30466e84ffe2 + hl-color:: yellow + - The amount of I/O generated by the open is proportional to the length of the pathname. + ls-type:: annotation + hl-page:: 537 + hl-color:: yellow + id:: 643ab82b-d15c-4298-b52b-30c27da1deb0 + - Read: first consult the file's inode for block address, and may update `access_time` field in the inode after read. + - Writing A File To Disk + ls-type:: annotation + hl-page:: 537 + hl-color:: yellow + id:: 643ab83e-d2fe-4f02-b467-b969ab2482cc + - Write (with new block allocation): besides the cost of `open`, write to new block needs 5 IOs: read-write data bitmap (to allocate new free block), read-write inode (give the new block to the file), and finally write the block itself. + - Create: First of all, walk the path to its parent directory (a lot of IOs similar to `open`). Then, read-write inode bitmap (to allocate new inode block), write the new inode, read-write parent inode. Finally, if the directory block cannot accommodate the new file, more IOs generated. + - Caching and Buffering + ls-type:: annotation + hl-page:: 539 + hl-color:: yellow + id:: 643abc13-2fdb-4a66-932a-eea1eafa449a + - static partitioning: a fixed-size cache to hold popular blocks with swap strategies such as LRU. Can be wasteful, though + hl-page:: 539 + ls-type:: annotation + id:: 643abc6f-93a1-44e8-bb62-e56b2a9f2541 + hl-color:: yellow + - dynamic partitioning: modern OSs integrate VM pages and FS pages into a unified page cache + hl-page:: 539 + ls-type:: annotation + id:: 643abc73-d5b4-4627-9ab9-ef8863bc8f3d + hl-color:: yellow + - write buffering: FS can batch some updates into one IO to disk; FS can schedule subsequent IOs; some writes can be eliminated (such as an overwrite) + hl-page:: 540 + ls-type:: annotation + id:: 643abc3c-040a-4f2f-89e4-ca14c9c0c230 + hl-color:: yellow +- akin 相似的；类似的: + ls-type:: annotation + hl-page:: 532 + hl-color:: green + id:: 643a96a0-f55d-4a84-bf93-4732a282b124 +- readily 容易地；乐意地； + ls-type:: annotation + hl-page:: 533 + hl-color:: green + id:: 643a96cb-bb7d-44c7-ac86-1e55a7ea3249 +- per se 本质上，本身 by itself + hl-page:: 534 + ls-type:: annotation + id:: 643a9be6-58e7-47a5-9ef2-bfff1f4c88a7 + hl-color:: green +- bad mouth 说人坏话 + hl-page:: 541 + ls-type:: annotation + id:: 643abbf4-1d1a-4b32-9d91-345983406ce5 + hl-color:: green +- ## Fast File System + ls-type:: annotation + hl-page:: 544 + hl-color:: yellow + id:: 643abf69-04dc-428c-996d-b139cba0fa1f + collapsed:: true + - Problems with the rudimentary FS + - Data spread over the space, leading to long seek time between, e.g., inode and its data + - Free space get fragmented, making sequential read to a file slow + - Block size (512B) too small + - On-disk Structure + hl-page:: 546 + ls-type:: annotation + id:: 643ac12f-817c-459b-b9ba-bbb1745519fb + hl-color:: yellow + - **cylinder**: ==a set of tracks== on different surfaces of a hard drive that are the ==same distance from the center== of the drive + hl-page:: 546 + ls-type:: annotation + id:: 643ac141-3bff-4b00-9c18-57ad7c108fe5 + hl-color:: yellow + - **cylinder groups**: aggregates consecutive cylinders into a group + hl-page:: 546 + ls-type:: annotation + id:: 643ac144-24f3-46ca-9354-47c9d2f4ffe0 + hl-color:: yellow + - **block groups**: modern HDDs tend not to expose internal structure, so the OS cannot have cylinder groups. Instead, organize the drive into block groups (they are consecutive anyways). + hl-page:: 547 + ls-type:: annotation + id:: 643ac1ec-08d9-4584-b6ed-4332f8f791a0 + hl-color:: yellow + - FFS spreads the components of a FS into each cylinder group. + - Each group has a copy of the super block. + - A per-group inode bitmap and data bitmap, keeping free block info in the group + - The remaining blocks are data blocks. + - Allocation Policies + hl-page:: 548 + ls-type:: annotation + id:: 643ac42c-edf9-4b68-8890-b04d724c2ac2 + hl-color:: yellow + - Basic mantra: Keep related stuff together. + - **Directory** placement: put the new directory in the cylinder group with a ==low number of allocated directories== (to balance directories across groups) and a ==high number of free inodes== (to subsequently be able to allocate a bunch of files) + hl-page:: 548 + ls-type:: annotation + id:: 643ac55f-b4a2-4bfc-ad0b-23c785c4871e + hl-color:: yellow + - **File** placement: data blocks of a file in the ==same group as its inode== (long seeks between inode and data) , and it places files that are in the ==same directory== into the cylinder group of their enclosing directory. + hl-page:: 548 + ls-type:: annotation + id:: 643ac616-ab90-40d5-94b2-7b8c294c4360 + hl-color:: yellow + - The Large-File Exception + ls-type:: annotation + hl-page:: 551 + hl-color:: yellow + id:: 643ac8cc-7164-4066-9730-231063c6c7c0 + - Large file hurts locality by filling up the group and preventing other related files being placed in the same group + - After some number of blocks are allocated into the first block group, FFS places the next "l==arge" chunk of the file in another block group==. For example, put blocks pointed by direct pointers (12 blocks) in the first group, and those pointed to by the indirect block (1K blocks) in another. + hl-page:: 551 + ls-type:: annotation + id:: 643ac9e7-1479-4be9-81fe-acb750f363b4 + hl-color:: yellow + - Potential Performance: large sequential read from a large file. However, with selected chunk size (threshold of going to another group), ==cost of seek between groups can be amortized==. The larger size of a chunk, the higher average bandwidth you will reach. + - Measuring File Locality + hl-page:: 550 + ls-type:: annotation + id:: 643ac769-6511-4954-a43a-957f3b561c56 + hl-color:: yellow + - The metric can be: the distance to the common ancestor of the 2 files which are consecutively opened. + - About 40% are either the same or under same directory (FFS captures this), and 25% have distance of 2 (FFS failed to capture this) + - A Few Other Things About FFS + hl-page:: 553 + ls-type:: annotation + id:: 643acef0-5592-4bad-8557-878567dc18a1 + hl-color:: yellow + divide block into sub-blocks to save disk space (4K is too large for small files), and modify *libc* to buffer writes in 4KB chunks; + parameterization, a different disk block layout to improve sequential read +- replica 复制品 + ls-type:: annotation + hl-page:: 547 + hl-color:: green + id:: 643ac2c5-a62f-473b-b0e5-32807c7b2e6a +- corollary 必然的结果(或结论) + hl-page:: 548 + ls-type:: annotation + id:: 643ac41b-c2e0-4351-b0e3-012e792cf426 + hl-color:: green +- extensive 广阔的，广泛的；大量的，大规模的 + ls-type:: annotation + hl-page:: 549 + hl-color:: green + id:: 643ac4ec-df99-430a-9e2e-78101c74b14e +- nuance (意义、声音、颜色、感情等方面的)细微差别 + hl-page:: 549 + ls-type:: annotation + id:: 643ac4f0-6809-4acd-b141-2a96174f5395 + hl-color:: green +- watershed 分水岭 + hl-page:: 555 + ls-type:: annotation + id:: 643acd1b-5a18-4b14-acdc-006c2f97c0e8 + hl-color:: green +- ## Crash Consistency + hl-page:: 558 + ls-type:: annotation + id:: 643acfc2-eef7-4c7f-a8a5-1740c8788159 + hl-color:: yellow \ No newline at end of file