Re: [PATCH] filemap_fdatasync & related changes

[Daniel Phillips <phillips@innominate.de>]

Chris Mason wrote:
> 
> Hi guys,
> 
> Just noticed the filemap_fdatasync code doesn't check the return value from
> writepage.  Linus, would you take a patch that redirtied the page, puts it
> back onto the dirty list (at the tail), and unlocks the page when writepage
> returns 1?

It would be a lot more consistent if ->writepage always unlocks the page
(or starts the chain of events that eventually unlocks the page) even
when it fails.

> That would loop forever if the writepage func kept returning 1 though...I
> think that's what we want, unless someone like ramfs made a writepage func
> that always returned 1.

Even then it's ok.  Without major surgery, those pages are going to loop
forever somewhere, it might as well be the inactive_dirty list.  This is
going to mess up the mm balancing calculations, but of course only when
somebody is actually using ramfs.  Maybe somebody will come up with a
tidy way of getting those pages entirely off the mm lists so they doing
just keep eating cpu cycles.

By the way, the whole concept of ramfs is really elegant - ramdisks are
just wrong, because all the ramdisk data in cache is in memory twice. 
Solution: throw away the disk, keep the cache.  Nice.

> For the reiserfs code, I'd like to be able to tell page_launder and
> filemap_fdatasync to try the page again later.  reiserfs would clean and
> unlock the page if no io needs to be done at all.

--
Daniel
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