linux-ext4 - Re: how to disable readahead

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Date:   Thu, 2 Aug 2018 15:01:29 +0000
From:   "Bean Huo (beanhuo)" <beanhuo@...ron.com>
To:     Jack Wang <jack.wang.usish@...il.com>
CC:     "tytso@....edu" <tytso@....edu>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        "beanhuo.linux@...gle.com" <beanhuo.linux@...gle.com>
Subject: Re: how to disable readahead

>
>> I am newbie on ext4, I tried the above method to disable readahead, echo
>0 > /sys/block/<dev>/queue/read_ahead_kb
>> Then I read by 128kB chunk size, ext4 will read the file by 4KB chunk size
>each time. that means ext4 splits 128KB into 32 4KB to read.
>> That's not my expectation.
>> Do you know how to still keep and let ext4 read by 128KB in case of disable
>readahead?
>> Thanks.
>>
>> //bean huo
>I guess you're doing buffered IO, have you try to use direct IO?
>
Direct I/O is another case, it is true that will bypass readahead.
But I want to disable readahead with page cache.

>Cheers,
>Jack