Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
To:     "linux-mm@kvack.org" <linux-mm@kvack.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
From:   Yang Shi <yang.shi@linux.alibaba.com>
Subject: [Question] Why PageReadahead is not migrated by migration code?
Message-ID: <7691ab12-2e84-2531-f27d-2fae9045576d@linux.alibaba.com>
Date:   Thu, 13 Feb 2020 09:06:58 -0800
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0)
 Gecko/20100101 Thunderbird/52.7.0
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Content-Language: en-US
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi folks,


Recently we saw some PageReadahead related bugs, so I did a quick check 
about the use of PageReadahead. I just found the state is *not* migrated 
by migrate_page_states().


Since migrate_page() won't migrate writeback page, so if PageReadahead 
is set it should just mean PG_readahead rather than PG_reclaim. So, I 
didn't think of why it is not migrated.


I dig into the history a little bit, but the change in migration code is 
too overwhelming. But, it looks PG_readahead was added after migration 
was introduced. Is it just a simple omission?


Thanks,

Yang