Re: [PATCH] mm: readahead: remove redundant ra_pages in file_ra_state

[Ni zhan Chen]

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?

Regards,
Chen

> Thanks,
> Fengguang
>
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