Messages in this thread | | | Date | Fri, 26 Oct 2012 15:09:36 +0800 | From | Fengguang Wu <> | Subject | Re: [PATCH] mm: readahead: remove redundant ra_pages in file_ra_state |
| |
On Fri, Oct 26, 2012 at 03:03:12PM +0800, Ni zhan Chen wrote: > On 10/26/2012 02:58 PM, Fengguang Wu wrote: > >> static void shrink_readahead_size_eio(struct file *filp, > >> struct file_ra_state *ra) > >> { > >>- ra->ra_pages /= 4; > >>+ spin_lock(&filp->f_lock); > >>+ filp->f_mode |= FMODE_RANDOM; > >>+ spin_unlock(&filp->f_lock); > >> > >>As the example in comment above this function, the read maybe still > >>sequential, and it will waste IO bandwith if modify to FMODE_RANDOM > >>directly. > >Yes immediately disabling readahead may hurt IO performance, the > >original '/ 4' may perform better when there are only 1-3 IO errors > >encountered. > > Hi Fengguang, > > Why the number should be 1-3?
The original behavior is '/= 4' on each error.
After 1 errors, readahead size will be shrinked by 1/4 After 2 errors, readahead size will be shrinked by 1/16 After 3 errors, readahead size will be shrinked by 1/64 After 4 errors, readahead size will be effectively 0 (disabled)
Thanks, Fengguang
| |