linux-ext4 - Re: how to disable readahead

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Message-ID: <CA+res+TRZEHKNnyZnCifasjvmJiY_ccKeiaV56rZM8a2LxUoRA@mail.gmail.com>
Date:   Thu, 2 Aug 2018 16:03:12 +0200
From:   Jack Wang <jack.wang.usish@...il.com>
To:     beanhuo@...ron.com
Cc:     tytso@....edu, linux-ext4@...r.kernel.org, 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?

Cheers,
Jack