linux-kernel - [Question] Why PageReadahead is not migrated by migration code?

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Date:   Thu, 13 Feb 2020 09:06:58 -0800
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: [Question] Why PageReadahead is not migrated by migration code?

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