Re: [PATCH 14/33] readahead: state based method - data structure

[Wu Fengguang]

On Fri, May 26, 2006 at 10:05:52AM -0700, Andrew Morton wrote:
> Wu Fengguang <wfg@xxxxxxxxxxxxxxxx> wrote:
> >
> >  #define RA_FLAG_MISS 0x01	/* a cache miss occured against this file */
> >   #define RA_FLAG_INCACHE 0x02	/* file is already in cache */
> >  +#define RA_FLAG_MMAP		(1UL<<31)	/* mmaped page access */
> >  +#define RA_FLAG_NO_LOOKAHEAD	(1UL<<30)	/* disable look-ahead */
> >  +#define RA_FLAG_EOF		(1UL<<29)	/* readahead hits EOF */
> 
> Odd.  Why not use 4, 8, 16?

Sorry, the lower 8 bits are for ra_class values in the new code. It can
cause data corruption when dynamic switching between the two logics :(

I'd like to change the flags member to explicit ones like

        struct {
                unsigned miss           :1;
                unsigned incache        :1;
                unsigned mmap           :1;
                unsigned no_lookahead   :1;
                unsigned eof            :1;
        } flags;

        unsigned class_new              :4;
        unsigned class_old              :4;

Reasonable?
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