Re: [Patch] invalidate range of pages after direct IO write

[Andrew Morton <akpm@osdl.org>]

Zach Brown <zach.brown@oracle.com> wrote:
>
> After a direct IO write only invalidate the pages that the write intersected.
> invalidate_inode_pages2_range(mapping, pgoff start, pgoff end) is added and
> called from generic_file_direct_IO().  This doesn't break some subtle agreement
> with some other part of the code, does it?

It should be OK.

Note that the same optimisation should be made in the call to
unmap_mapping_range() in generic_file_direct_IO().  Currently we try and
unmap the whole file, even if we're only writing a single byte.  Given that
you're now calculating iov_length() in there we might as well use that
number a few lines further up in that function.

Note that invalidate_inode_pages[_range2] also does the unmapping thing -
in the direct-io case we don't expect that path th ever trigger: the only
way we'll find mapped pages here is if someone raced and faulted a page
back in.

Reading the code, I'm unable to convince myself that it won't go into an
infinite loop if it finds a page at page->index = -1.  But I didn't try
very hard ;)

Minor note on this:

	return invalidate_inode_pages2_range(mapping, 0, ~0UL);

I just use `-1' there.  We don't _know_ that pgoff_t is an unsigned long. 
Some smarty may come along one day and make it unsigned long long, in which
case the code will break.  Using -1 here just works everywhere.

I'll make that change and plop the patch into -mm, but we need to think
about the infinite-loop problem..