On Tue, 29 Nov 2011 11:23:23 +0800 Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> > > +{
> > > +#ifdef CONFIG_READAHEAD_STATS
> > > + if (readahead_stats_enable) {
> > > + readahead_stats(mapping, offset, req_size, ra_flags,
> > > + start, size, async_size, actual);
> > > + readahead_stats(mapping, offset, req_size,
> > > + RA_PATTERN_ALL << READAHEAD_PATTERN_SHIFT,
> > > + start, size, async_size, actual);
> > > + }
> > > +#endif
> > > +}
> >
> > The stub should be inlined, methinks. The overhead of evaluating and
> > preparing eight arguments is significant. I don't think the compiler
> > is yet smart enough to save us.
>
> The parameter list actually becomes even out of control when doing the
> bit fields:
>
> + readahead_event(mapping, offset, req_size,
> + ra->pattern, ra->for_mmap, ra->for_metadata,
> + ra->start + ra->size >= eof,
> + ra->start, ra->size, ra->async_size, actual);
>
> So I end up passing file_ra_state around. The added cost is, I'll have
> to dynamically create a file_ra_state for the fadvise case, which
> should be acceptable since it's a cold path.
That will reduce the cost of something which would have zero cost by
making this function a static inline when CONFIG_READAHEAD_STATS=n.
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