Re: [PATCH v5.1] fs: Allow fine-grained control of folio sizes

[Dave Chinner <david@fromorbit.com>]

On Tue, May 28, 2024 at 09:12:02AM +0000, Pankaj Raghav (Samsung) wrote:
> On Tue, May 28, 2024 at 09:00:00AM +1000, Dave Chinner wrote:
> > On Mon, May 27, 2024 at 11:43:43PM +0100, Matthew Wilcox wrote:
> > > On Mon, May 27, 2024 at 11:39:47PM +0100, Matthew Wilcox wrote:
> > > > > > +	AS_FOLIO_ORDER_MIN = 16,
> > > > > > +	AS_FOLIO_ORDER_MAX = 21, /* Bits 16-25 are used for FOLIO_ORDER */
> > > > > >  };
> > > > > >  
> > > > > > +#define AS_FOLIO_ORDER_MIN_MASK 0x001f0000
> > > > > > +#define AS_FOLIO_ORDER_MAX_MASK 0x03e00000
> > > > > 
> > > > > As you changed the mapping flag offset, these masks also needs to be
> > > > > changed accordingly.
> > > > 
> > > > That's why I did change them?
> > > 
> > > How about:
> > > 
> > > -#define AS_FOLIO_ORDER_MIN_MASK 0x001f0000
> > > -#define AS_FOLIO_ORDER_MAX_MASK 0x03e00000
> > > +#define AS_FOLIO_ORDER_MIN_MASK (31 << AS_FOLIO_ORDER_MIN)
> > > +#define AS_FOLIO_ORDER_MAX_MASK (31 << AS_FOLIO_ORDER_MAX)
> > 
> > Lots of magic numbers based on the order having only having 5 bits
> > of resolution. Removing that magic looks like this:
> > 
> > 	AS_FOLIO_ORDER_BITS = 5,
> 
> I think this needs to be defined outside of the enum as 5 is already
> taken by AS_NO_WRITEBACK_TAGS? But I like the idea of making it generic
> like this.

Duplicate values in assigned enums are legal and fairly common.
This:

enum {
        FOO = 1,
        BAR = 2,
        BAZ = 1,
};

int main(int argc, char *argv[])
{
        printf("foo %d, bar %d, baz %d\n", FOO, BAR, BAZ);
}

compiles without warnings or errors and gives the output:

foo 1, bar 2, baz 1

-Dave.
-- 
Dave Chinner
david@fromorbit.com