Re: [RFC PATCH 0/7] mm: Make more use of readahead_control

[Matthew Wilcox]

On Tue, Sep 01, 2020 at 08:44:14PM +0100, David Howells wrote:
> Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> 
> > > Note that I've been
> > > passing the number of pages to read in rac->_nr_pages, and then saving it
> > > and changing it certain points, e.g. page_cache_readahead_unbounded().
> > 
> > I do not like this.  You're essentially mutating the meaning of _nr_pages
> > as the ractl moves down the stack, and that's going to lead to bugs.
> > I'd keep it as a separate argument.
> 
> The meaning isn't specified in linux/pagemap.h.  Can you adjust the comments
> on the struct and on readahead_count() to make it more clear what the value
> represents?

It's intentionally not documented.  This documentation is for the
filesystem author, who should not be looking at it.  Neither should
you :-P