Re: [patch 1/2] mm: dont clear PG_uptodate in invalidate_complete_page2()

[Evgeniy Polyakov <johnpol@2ka.mipt.ru>]

On Wed, Jun 25, 2008 at 05:59:14PM +0200, Miklos Szeredi (miklos@szeredi.hu) wrote:
> > Page is locked of course, but invalidated, removed from all trees and
> > caches, i.e. grab, lock, check, unlock... invalidate, write into that
> > page should fail, but it will not, since page is uptodate and
> > prepare_write does not check mapping at all.
> 
> But callers do check after having locked the page.

Yes, it is possible to check mapping, but it does not exist and it is
correct, that there is no mapping - we are just writing into page in
ram, kind of loop device, but without binding page into mapping.
And mapping itself is used just for its operations.

> > > > Instead of returning error when reading from invalid page, now you
> > > > return old content of it?
> > > 
> > > No, instead of returning a short count, it is now returning old
> > > content.
> > 
> > Or instead of returning error or zero and relookup page eventually,
> > which can already contain new data, we get old data.
> 
> Umm, it doesn't make any sense to try to always get fresh data.  If
> you do read() on a file, the data may become old and invalid a
> millisecond after the read finished.  We can't and needn't do anything
> about this.

Page reading from disk is atomic in respect that page is always locked,
now readpage(s) may not be called in some cases...

-- 
	Evgeniy Polyakov