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    SubjectRe: [PATCH v2 2/4] mm: add file_fdatawait_range and file_write_and_wait
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    On Thu, 2017-07-27 at 10:49 +0200, Jan Kara wrote:
    > On Wed 26-07-17 13:55:36, Jeff Layton wrote:
    > > +int file_write_and_wait(struct file *file)
    > > +{
    > > + int err = 0, err2;
    > > + struct address_space *mapping = file->f_mapping;
    > > +
    > > + if ((!dax_mapping(mapping) && mapping->nrpages) ||
    > > + (dax_mapping(mapping) && mapping->nrexceptional)) {
    > > + err = filemap_fdatawrite(mapping);
    > > + /* See comment of filemap_write_and_wait() */
    > > + if (err != -EIO) {
    > > + loff_t i_size = i_size_read(mapping->host);
    > > +
    > > + if (i_size != 0)
    > > + __filemap_fdatawait_range(mapping, 0,
    > > + i_size - 1);
    > > + }
    > > + }
    >
    > Err, what's the i_size check doing here? I'd just pass ~0 as the end of the
    > range and ignore i_size. It is much easier than trying to wrap your head
    > around possible races with file operations modifying i_size.
    >
    > Honza

    I'm basically emulating _exactly_ what filemap_write_and_wait does here,
    as I'm leery of making subtle behavior changes in the actual writeback
    behavior. For example:

    -----------------8<----------------
    static inline int __filemap_fdatawrite(struct address_space *mapping,
    int sync_mode)
    {
    return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
    }

    int filemap_fdatawrite(struct address_space *mapping)
    {
    return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
    }
    EXPORT_SYMBOL(filemap_fdatawrite);
    -----------------8<----------------

    ...which then sets up the wbc with the right ranges and sync mode and
    kicks off writepages. But then, it does the i_size_read to figure out
    what range it should wait on (with the shortcut for the size == 0 case).

    My assumption was that it was intentionally designed that way, but I'm
    guessing from your comments that it wasn't? If so, then we can turn
    file_write_and_wait a static inline wrapper around
    file_write_and_wait_range.
    --
    Jeff Layton <jlayton@redhat.com>

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