Re: Question about invalidate_inode_pages2_range()

[Trond Myklebust <trond.myklebust@fys.uio.no>]

On Mon, 2009-10-19 at 16:38 +0800, Peng Tao wrote:
> On Mon, Oct 19, 2009 at 4:26 PM, Trond Myklebust
> <trond.myklebust@fys.uio.no> wrote:
> > On Mon, 2009-10-19 at 16:16 +0800, Peng Tao wrote:
> >> Hi,
> >>
> >> I've a question about invalidate_inode_pages2_range().
> >>
> >> When does invalidate_inode_pages2_range() returns -EBUSY? It locks and
> >> writes back the page. Why invalidate_complete_page2() still may fail
> >> due to page dirtiness?
> >
> > A lot of those requirements were set by NFS, which uses
> > invalidate_inode_pages2() in order to invalidate the page cache when it
> > detects that a file has been changed on the server (either due to an
> > O_DIRECT write, or due to another client modifying the file).
> >
> > In such cases, you want to try to keep the dirty data by writing it out
> > instead of discarding it.
> Thanks for your quick response. But I have two more questions about this.
> 1. invalidate_inode_pages2_range() calls wait_on_page_writeback().
> Does the latter actually write out the dirty page?

No. It just waits for any outstanding writeback activity on that page to
finish.

> 2. Is there any interface in the mm subsystem forces discarding a page cache?

You mean that also discards dirty pages? Yes. That is what
truncate_inode_pages() does...