Re: [PATCH 04/33] readahead: page flag PG_readahead

[Wu Fengguang]

On Thu, May 25, 2006 at 09:23:11AM -0700, Andrew Morton wrote:
> Wu Fengguang <wfg@xxxxxxxxxxxxxxxx> wrote:
> >
> > An new page flag PG_readahead is introduced as a look-ahead mark, which
> > reminds the caller to give the adaptive read-ahead logic a chance to do
> > read-ahead ahead of time for I/O pipelining.
> > 
> > It roughly corresponds to `ahead_start' of the stock read-ahead logic.
> > 
> 
> This isn't a very revealing description of what this flag does.

Updated to:

An new page flag PG_readahead is introduced.

It acts as a look-ahead mark, which tells the page reader:
        Hey, it's time to invoke the adaptive read-ahead logic!
        For the sake of I/O pipelining, don't wait until it runs out of
        cached pages.  ;-)

> > +#define __SetPageReadahead(page) __set_bit(PG_readahead, &(page)->flags)
> 
> uh-oh.  This is extremly risky.  Needs extensive justification, please.

Ok, removed the ugly __ :-)

Wu
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