Messages in this thread | | | Date | Fri, 26 Oct 2012 15:19:57 +0800 | From | Ni zhan Chen <> | Subject | Re: [PATCH] mm: readahead: remove redundant ra_pages in file_ra_state |
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On 10/26/2012 03:09 PM, Fengguang Wu wrote: > 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)
But from function shrink_readahead_size_eio and its caller filemap_fault I can't find the behavior you mentioned. How you figure out it?
Regards, Chen
> > Thanks, > Fengguang >
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