On Wed, Nov 03, 2021 at 02:58:12PM +0000, David Howells wrote:

Matthew Wilcox [off-list ref] wrote:

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+	len = (size >= start + gran) ? gran : size - start;

This seems like the most complicated way to write this ... how about:

        size_t len = min_t(loff_t, isize - start, folio_size(folio));

I was trying to hedge against isize-start going negative.  Can this code race
against truncate?  truncate_setsize() changes i_size *before* invalidating the
pages.

We should check for isize < start separately, and skip the writeback
entirely.

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 static int afs_symlink_readpage(struct file *file, struct page *page)
 {
-	struct afs_vnode *vnode = AFS_FS_I(page->mapping->host);
+	struct afs_vnode *vnode = AFS_FS_I(page_mapping(page)->host);

How does swap end up calling readpage on a symlink?

Um - readpage is called to read the symlink.

But the only reason to use page_mapping() instead of page->mapping
is if you don't know that the page is in the page cache.  You know
that here, so I don't understand why you changed it.

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-	page_endio(page, false, ret);
+	page_endio(&folio->page, false, ret);

We need a folio_endio() ...

I think we mentioned this before and I think you said you had or would make a
patch for it.  I can just create a wrapper for it if that'll do.

Probably better to convert it and put a page_endio wrapper in
folio-compat.c