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SubjectRe: [patch 1/2] mm: dont clear PG_uptodate in invalidate_complete_page2()
On Wed, Jun 25, 2008 at 02:40:39PM +0200, Miklos Szeredi (miklos@szeredi.hu) wrote:
> From: Miklos Szeredi <mszeredi@suse.cz>
>
> Clearing the uptodate page flag will cause page_cache_pipe_buf_confirm()
> to return -ENODATA if that page was in the buffer. This in turn will cause
> splice() to return a short or zero count.
>
> This manifested itself in rare I/O errors seen on nfs exported fuse
> filesystems. This is because nfsd uses splice_direct_to_actor() to
> read files, and fuse uses invalidate_inode_pages2() to invalidate
> stale data on open.
>
> Fix this by not clearing PG_uptodate on page invalidation. This will
> result in the old, invalid page contents being copied. But that's OK,
> the contents were valid at splice-in time (which is when the the
> "copy" was conceptually done).
>
> I haven't done an audit of all code that checks the PG_uptodate flags,
> but I suspect, that this change won't have any harmful effects. Most
> code checks page->mapping to see if the page was truncated or
> invalidated, before using it, and retries the find/read on the page if
> it wasn't. The page_cache_pipe_buf_confirm() code is an exception in
> this regard.

What about writing path, when page is written after some previous write?
Like __block_prepare_write()?

> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
> ---
> mm/truncate.c | 1 -
> 1 file changed, 1 deletion(-)
>
> Index: linux-2.6/mm/truncate.c
> ===================================================================
> --- linux-2.6.orig/mm/truncate.c 2008-06-24 20:49:25.000000000 +0200
> +++ linux-2.6/mm/truncate.c 2008-06-24 23:28:32.000000000 +0200
> @@ -356,7 +356,6 @@ invalidate_complete_page2(struct address
> BUG_ON(PagePrivate(page));
> __remove_from_page_cache(page);
> write_unlock_irq(&mapping->tree_lock);
> - ClearPageUptodate(page);
> page_cache_release(page); /* pagecache ref */
> return 1;
> failed:

Don't do that, add new function instead which will do exactly that, if
you do need exactly this behaviour.

Also why isn't invalidate_complete_page() enough, if you want to have
that page to be half invalidated?

--
Evgeniy Polyakov


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