Messages in this thread | | | From | "Stephen C. Tweedie" <> | Date | Mon, 7 Feb 2000 15:39:15 +0000 (GMT) | Subject | Re: ext2 compression status (was Re: 2.4 Features |
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Hi,
On Sun, 6 Feb 2000 11:37:27 +1100, Peter Moulder <reiter@netspace.net.au> said:
>> and is there a robust 2.3 version?
> Nope. The change to Linux' write mechanism in early 2.3 (namely > having writes go through writepage instead of having ext2_file_write > create disk buffers) means that there's no longer a convenient place > to do the compression (in the most common case, where we wish to > compress more than a page full at a time). Probably the fix is to > organise for multiple pages to be written at once. It just requires > that someone spend a chunk of time getting familiar with how pages > usually get written out, and the locking issues and so on. Stephen, > since you're already familiar with both the mm system and ext2, can > you comment on that plan?
Sure. It's not really hard to do that in 2.3.
The 2.3 VM doesn't force you to use generic_file_write(). grab_cache_page() and read_cache_page() can be used by other filesystems to access the page cache, and you can use that in your own file_write function to do any sort of transformations you want during the write() system call. You don't want to use generic_file_write(), as that assumes that the disk blocks we're using for IO correspond exactly to the contents of the page cache. That doesn't prevent you from using your own file_write function to update the page cache and then do any other write-through you want to the buffer cache.
--Stephen
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