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 This document has been retrieved from archive.org in its version from 2007-04-27.
It was written by its respective author(s) and not by the author(s) of this article.
Please apply only formatting changes, adding or correcting sources and maybe
spelling- and punctuation fixes to this document. Thanks!
 Tasks are needed to done for getting reiser4 code into the kernel 
 as found by AKPM in 2.6.18-rc2-mm1 (# means that an issue is done)
 Reiser4/ToDo (last edited 2007-04-27 10:20:13 by frink)
Tasks are needed to done for getting reiser4 code into the kernel as found by AKPM
in 2.6.18-rc2-mm1 (# means that an issue is done)

1. running igrab() in the writepage() path is really going to hammer inode_lock. 
   Something else will need to be done here.

2. The preferred way of solving the above would be to mark the page as
   PageWriteback() with set_page_writeback() prior to unlocking it. That'll pin
   the page and the inode. It does require that the page actually get written later on.
   If we cannot do that then more thought is needed.

3. If poss, use wake_up_process() rather than wake_up(). That'll save some locking.

4. Running iput() in entd() is a bit surprising. iirc there are various ways in which
   this can recur into the filesystem, perform I/O, etc. I guess it works.. But again,
   it will hammer inode_lock.

5. the writeout logic in entd_flush() is interesting (as in "holy cow"). It's very
   central and really needs some good comments describing what's going on in there - 
   what problems are being solved, which decisions were taken and why, etc. The big 
   comment in page_cache.c is useful. Please maintain it well. Boy, it has some old 
   stuff in it.

6. reiser4_wait_page_writeback() needs commenting.

7. reading the comment in txnmgr.c regarding MAP_SHARED pages: a number of things
   have changed since then. We have page-becoming-writeable notifications and probably
   soon we'll always take a pagefault when a MAP_SHARED page transitions from pte-clean
   to pte-dirty (although I wouldn't recommend that a filesystem rely upon the latter
   for a while yet).

8. page_cache.c: yes, mpage_end_io_write() and mpage_end_io_read() are pretty generic
   - we might as well export them.

9. truncate_jnodes_range() looks wrong to me. When we populate gang[], there can be any
   number of NULL entries placed in it. But the loop which iterates across the 
   now-populated gang[] will bale out when it its the _first_ NULL entry. Any following 
   entries will have a leaked jref() against them.

10. Waaaaaaaaaaaaaaay too many typedefs.

11. There are many coding-style nits. One I will mention is very large number of unneeded braces:
          * if (foo) {
                o bar(); 
      it'd be nice to fix these up sometime. Note: Easy to find and repair with checkpatch.pl
script found at http://www.kernel.org/pub/linux/kernel/people/apw/checkpatch/

12. General comment: the lack of support for extended attributes, access control lists and 
    direct-io is a big problem and it's getting bigger. I don't see how a vendor could 
    support reiser4 without these features and permanent lack of vendor support will hurt. 
    What's the plan here?

13. (from CH) Another issue is the lack of support for blocksize < pagesize. This prevents it 
    from being used across architectures. Even worse when I tried the last time it didn't allow
    me to create a 64k blocksize filesystem that I could actually test on ppc64.  \

14. set_page_dirty_internal() pokes around in VFS internals. Use set_page_dirty_no_buffers() 
    or create a new library function in mm/page-writeback.c. In particular, it gets the 
    radix-tree dirty tagging out of sync.

15. #wbq.sem should be using a completion for the "wait until entd finishes", not a semaphore.
    Because there's a teeny theoretical race when using semaphores this way which completions
    were designed to avoid. (The waker can still be playing with the semaphore when it has 
    gone out of scope on the wakee's stack).

16. #write_page_by_ent(): the "spin until entd thread" thing is gross. This function is really

17. #entd_flush(): bug:
       rq->wbc->range_start = rq->page->index << PAGE_CACHE_SHIFT; 
    this can overflow on 32-bit. Need to cast rq->page->index to loff_t.

18. #writeout() is a poor name for a global function. Even things like "txn_restart" are a bit
    generic-sounding. Low-risk, but the kernel's getting bigger... If it were mine, I'd prefix
    all these symbols with "r4_". prepare_to_sleep(), page_io(), drop_page(), statfs_type(), 
    pre_commit_hook(), etc, etc, etc, etc. Much namespace pollution.

19. #invalidate_list() is a poorly-chosen global identifier. We already have an invalidate_list()
    in fs/inode.c, too. Please audit all of reiser4's global identifiers (use nm *.o) for 
    suitable naming choices.

20. #semaphores are deprecated. Please switch to mutexes and/or completions where appropriate 
    and possible.

21. #drop_page() is a worry. Why _does_ reiser4 need to remove pages from pagecache? That 
    isn't a filesystem function. drop_page() appears to leave the no-longer-present page tagged
    as dirty in the radix-tree.

22. #reiser4_invalidate_pages() is a mix of reiser4 things and of things-which-the-vfs-is-supposed-to-do.
    It is uncommented and I am unable to work out why it was necessary to do this, and hence what we 
    can do about it.

23. #reiser4_readpages() shouldn't need to clean up the remaining pages on *pages. read_cache_pages()
    does that now.

24. #<wonders what formatted and unformatted nodes are> A brief glossary might help.

25. #REISER4_ERROR_CODE_BASE actually overlaps real errnos (see include/linux/errno.h). Suggest that
    it be changed to 1000000 or something.

26. #blocknr_set_add() modifies a list_head without any apparent locking. Certainly without any 
    _documented_ locking... Ditto blocknr_set_destroy(). I'm sure there's locking, but it's harder than
    it should be to work out what it is. Given that proper locking is in place, the filesystem seems to
    use list_*_careful() a lot more than is necessary?

27. #It would be clearer to remove `struct blocknr_set' and just use list_head. 

Reiser4/ToDo (last edited 2007-11-25 21:57:14 by M9132)
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