Messages in this thread | | | From | "Stephen C. Tweedie" <> | Date | Mon, 18 Oct 1999 11:28:14 +0100 (BST) | Subject | Re: fs specific union in struct buffer head? Optimal implementation of allocate on flush seems to require a b_parent field in struct buffer_head. |
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Hi,
On Fri, 15 Oct 1999 23:22:23 +0400, Hans Reiser <reiser@idiom.com> said:
> Vladimir and I are discussing how to implement allocate on flush in our next > major version (not for 2.4) of reiserfs.
>> If you are going to reallocate on flush unformatted nodes you must be able >> to:
Remember, there is a huge difference between allocate-on-flush and reallocate-on-flush. In the former case, you simply don't have buffer_heads present until the final flush: everything has to be maintained in the filesystem itself or the VM, not in the buffer cache, until the final flush (because the buffer cache is really only for storing blocks whose on-disk location is known).
In the reallocate case, a buffer_head b_fs_private pointer to fs-specific metadata would allow the fs to deal with this independently of the buffer cache layer itself. For allocate-on-flush, though, you need to be able to look up the information from the VM, not from the buffer cache.
--Stephen
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