117 lines
5.0 KiB
Plaintext
117 lines
5.0 KiB
Plaintext
# @(#)TODO 8.1 (Berkeley) 6/11/93
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NOTE: Changed the lookup on a page of inodes to search from the back
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in case the same inode gets written twice on the same page.
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Make sure that if you are writing a file, but not all the blocks
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make it into a single segment, that you do not write the inode in
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that segment.
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Keith:
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Why not delete the lfs_bmapv call, just mark everything dirty
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that isn't deleted/truncated? Get some numbers about
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what percentage of the stuff that the cleaner thinks
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might be live is live. If it's high, get rid of lfs_bmapv.
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There is a nasty problem in that it may take *more* room to write
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the data to clean a segment than is returned by the new segment
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because of indirect blocks in segment 2 being dirtied by the data
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being copied into the log from segment 1. The suggested solution
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at this point is to detect it when we have no space left on the
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filesystem, write the extra data into the last segment (leaving
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no clean ones), make it a checkpoint and shut down the file system
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for fixing by a utility reading the raw partition. Argument is
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that this should never happen and is practically impossible to fix
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since the cleaner would have to theoretically build a model of the
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entire filesystem in memory to detect the condition occurring.
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A file coalescing cleaner will help avoid the problem, and one
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that reads/writes from the raw disk could fix it.
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DONE Currently, inodes are being flushed to disk synchronously upon
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creation -- see ufs_makeinode. However, only the inode
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is flushed, the directory "name" is written using VOP_BWRITE,
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so it's not synchronous. Possible solutions: 1: get some
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ordering in the writes so that inode/directory entries get
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stuffed into the same segment. 2: do both synchronously
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3: add Mendel's information into the stream so we log
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creation/deletion of inodes. 4: do some form of partial
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segment when changing the inode (creation/deletion/rename).
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DONE Fix i_block increment for indirect blocks.
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If the file system is tar'd, extracted on top of another LFS, the
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IFILE ain't worth diddly. Is the cleaner writing the IFILE?
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If not, let's make it read-only.
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DONE Delete unnecessary source from utils in main-line source tree.
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DONE Make sure that we're counting meta blocks in the inode i_block count.
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Overlap the version and nextfree fields in the IFILE
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DONE Vinvalbuf (Kirk):
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Why writing blocks that are no longer useful?
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Are the semantics of close such that blocks have to be flushed?
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How specify in the buf chain the blocks that don't need
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to be written? (Different numbering of indirect blocks.)
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Margo:
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Change so that only search one sector of inode block file for the
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inode by using sector addresses in the ifile instead of
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logical disk addresses.
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Fix the use of the ifile version field to use the generation
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number instead.
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DONE Unmount; not doing a bgetvp (VHOLD) in lfs_newbuf call.
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DONE Document in the README file where the checkpoint information is
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on disk.
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Variable block sizes (Margo/Keith).
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Switch the byte accounting to sector accounting.
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DONE Check lfs.h and make sure that the #defines/structures are all
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actually needed.
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DONE Add a check in lfs_segment.c so that if the segment is empty,
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we don't write it.
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Need to keep vnode v_numoutput up to date for pending writes?
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DONE USENIX paper (Carl/Margo).
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Evelyn:
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lfsck: If delete a file that's being executed, the version number
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isn't updated, and lfsck has to figure this out; case is the same as if have an inode that no directory references,
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so the file should be reattached into lost+found.
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Recovery/fsck.
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Carl:
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Investigate: clustering of reads (if blocks in the segment are ordered,
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should read them all) and writes (McVoy paper).
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Investigate: should the access time be part of the IFILE:
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pro: theoretically, saves disk writes
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con: cacheing inodes should obviate this advantage
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the IFILE is already humongous
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Cleaner.
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Port to OSF/1 (Carl/Keith).
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Currently there's no notion of write error checking.
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+ Failed data/inode writes should be rescheduled (kernel level
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bad blocking).
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+ Failed superblock writes should cause selection of new
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superblock for checkpointing.
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FUTURE FANTASIES: ============
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+ unrm, versioning
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+ transactions
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+ extended cleaner policies (hot/cold data, data placement)
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==============================
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Problem with the concept of multiple buffer headers referencing the segment:
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Positives:
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Don't lock down 1 segment per file system of physical memory.
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Don't copy from buffers to segment memory.
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Don't tie down the bus to transfer 1M.
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Works on controllers supporting less than large transfers.
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Disk can start writing immediately instead of waiting 1/2 rotation
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and the full transfer.
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Negatives:
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Have to do segment write then segment summary write, since the latter
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is what verifies that the segment is okay. (Is there another way
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to do this?)
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==============================
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The algorithm for selecting the disk addresses of the super-blocks
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has to be available to the user program which checks the file system.
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(Currently in newfs, becomes a common subroutine.)
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