Re: [PATCH] mm/filemap: Use filemap_read_page in filemap_fault

[Matthew Wilcox <willy@infradead.org>]

On Tue, Mar 02, 2021 at 05:30:39PM -0800, Andrew Morton wrote:
> On Fri, 26 Feb 2021 14:00:11 +0000 "Matthew Wilcox (Oracle)" <willy@infradead.org> wrote:
> 
> > After splitting generic_file_buffered_read() into smaller parts, it
> > turns out we can reuse one of the parts in filemap_fault().  This fixes
> > an oversight -- waiting for the I/O to complete is now interruptible
> > by a fatal signal.  And it saves us a few bytes of text in an unlikely
> > path.
> 
> We also handle AOP_TRUNCATED_PAGE which the present code fails to do. 
> Should this be in the changelog?

No, the present code does handle AOP_TRUNCATED_PAGE.  It's perhaps not
the clearest in the diff, but it's there.  Here's git show -U5:

-       ClearPageError(page);
        fpin = maybe_unlock_mmap_for_io(vmf, fpin);
-       error = mapping->a_ops->readpage(file, page);
-       if (!error) {
-               wait_on_page_locked(page);
-               if (!PageUptodate(page))
-                       error = -EIO;
-       }
+       error = filemap_read_page(file, mapping, page);
        if (fpin)
                goto out_retry;
        put_page(page);
 
        if (!error || error == AOP_TRUNCATED_PAGE)
                goto retry_find;
 
-       shrink_readahead_size_eio(ra);
        return VM_FAULT_SIGBUS;