linux-kernel - Re: [PATCH] mm: readahead: remove redundant ra_pages in file_ra

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Date:	Fri, 26 Oct 2012 15:03:12 +0800
From:	Ni zhan Chen <nizhan.chen@...il.com>
To:	Fengguang Wu <fengguang.wu@...el.com>
CC:	Dave Chinner <david@...morbit.com>,
	YingHang Zhu <casualfisher@...il.com>,
	akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: readahead: remove redundant ra_pages in file_ra_state

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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