On Wed, Oct 22 2008, Andrew Morton wrote:
> On Mon, 20 Oct 2008 20:11:56 +0200 Jens Axboe <jens.axboe@xxxxxxxxxx> wrote:
>
> > +ssize_t generic_file_splice_write_file_nolock(struct pipe_inode_info *pipe,
> > + struct file *out, loff_t *ppos,
> > + size_t len, unsigned int flags)
> > +{
> > + struct address_space *mapping = out->f_mapping;
> > + struct inode *inode = mapping->host;
> > + struct splice_desc sd = {
> > + .total_len = len,
> > + .flags = flags,
> > + .pos = *ppos,
> > + .u.file = out,
> > + };
> > + ssize_t ret;
> > +
> > + mutex_lock(&pipe->inode->i_mutex);
> > + ret = __splice_from_pipe(pipe, &sd, pipe_to_file);
> > + mutex_unlock(&pipe->inode->i_mutex);
> > +
> > + if (ret > 0) {
> > + unsigned long nr_pages;
> > +
> > + *ppos += ret;
> > + nr_pages = (ret + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
> > +
> > + if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
> > + int er;
> > +
> > + er = sync_page_range_nolock(inode, mapping, *ppos, ret);
> > + if (er)
> > + ret = er;
> > + }
> > + balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
> > + }
> > +
> > + return ret;
> > +}
> > +EXPORT_SYMBOL(generic_file_splice_write_file_nolock);
>
> I don't think the balance_dirty_pages() is needed if we just did the
> sync_page_range().
Good point, I think we can get rid of that.
>
>
> But really it'd be better if the throttling happened down in
> pipe_to_file(), on a per-page basis. As it stands we can dirty an
> arbitrary number of pagecache pages without throttling. I think?
That's pretty exactly why it isn't done in the actor, to avoid doing it
per-page. As it's going to be PIPE_BUFFERS (16) pages max, I think this
is better.
Back in the splice early days, the balance_dirty_pages() actually showed
up in profiles when it was done on a per-page basis. So I'm reluctant to
change it :-)
--
Jens Axboe
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