On Tue, 2007-02-20 at 10:40 -0800, Zach Brown wrote:
> >> There are some strange O_DIRECT corner cases in here such that the
> >> 'last
> >> writer' may actually be a 'last reader' and winning can mean have
> >> a copy
> >> of the page in page cache older than the copy on disk.
> >
> > As long as it is marked dirty so that it eventually gets synced to
> > disk,
> > it shouldn't matter.
>
> No, Chris is pointing out that an an O_DIRECT write can leave clean
> read pages in the page cache.
>
> All it takes is giving a source buffer for the write which is an mmap
> ()ed apeture of the region that is being written to. If you get the
> offsets right you can get the get_user_pages() down in fs/direct-io.c
> will populate the page cache before the actual O_DIRECT write gets to
> it.
With invalidate_inode_pages2()? That is supposed to wait until the page
lock is taken -> read is done. It then calls unmap_mapping_range() which
will remove the offending page from any existing mappings. Sure an
application could get stale data, but if it is reading while an O_DIRECT
write is proceeding, then it gets what it deserves.
Trond
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