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

[Fengguang Wu]

>  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.

Thanks,
Fengguang
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