On Wed, Apr 11, 2007 at 04:44:34AM +0000, Jin Steve wrote:
> Just like the function check_ra_success: (Does it mean: last time
> RA>VM_MAX_CACHE_HIT, so next time no need readahead?)
The cache hit logic is to prevent doing pointless readahead for
an already cached file: the pages are already there.
VM_MAX_CACHE_HIT is the threshold to disable readahead in this case.
> static inline int check_ra_success(struct file_ra_state *ra,
> unsigned long nr_to_read, unsigned long actual)
> {
> if (actual == 0) {
> ra->cache_hit += nr_to_read;
> if (ra->cache_hit >= VM_MAX_CACHE_HIT) {
> ra_off(ra);
> ra->flags |= RA_FLAG_INCACHE;
> return 0;
> }
> } else {
> ra->cache_hit=0;
> }
> return 1;
> }
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