Re: linux-2.4.10-pre5

[Andrea Arcangeli]

On Sat, Sep 08, 2001 at 11:01:59AM -0700, Linus Torvalds wrote:
> 
> On Sat, 8 Sep 2001, Andrea Arcangeli wrote:
> >
> > First of all I just __block_fsync + truncate_inode_pages(inode->i_mapping, 0) so
> > all pagecache updates are commited to disk after that, so the latest uptodate
> > data is on disk and nothing uptodate is in memory.
> 
> Hmm. And if two openers have the device open at the same time? One dirties

of course I described what happens under the bdev semaphore at the very
latest release, so there is no "two" opener case here. If some reference
of the file is still open I don't even attempt to sync anything. (if the
user didn't asked for O_SYNC of course, in such a case the
generic_file_write would take care of it)

> data after the first one has done __block_fsync? And the truncate will
> throw the dirtied page away?

There can't be any truncate because the blkdev isn't a regular file.

> Now, I don't think we need to be _too_ careful about cache coherency: it's
> probably ok to do something like
> 
> 	__block_fsync(dev) - sync _our_ changes
> 	invalidate_inode_pages(dev) - this will only invalidate unused pages
> 	invalidate_device(dev)

that's definitely not enough, see the other issue mentioned by Andreas
in this thread, the reason I wrote the algorithm I explained in the
previous email is as first thing to eventually avoid infinite long fsck
of the root fs.

Andrea