linux-kernel - Re: a question of split_huge

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Message-ID: <20200709155002.GF12769@casper.infradead.org>
Date:   Thu, 9 Jul 2020 16:50:02 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Linux-MM <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: a question of split_huge_page

On Thu, Jul 09, 2020 at 11:11:11PM +0800, Alex Shi wrote:
> Hi Kirill & Matthew,
> 
> In the func call chain, from split_huge_page() to lru_add_page_tail(),
> Seems tail pages are added to lru list at line 963, but in this scenario
> the head page has no lru bit and isn't set the bit later. Why we do this?
> or do I miss sth?

I don't understand how we get to split_huge_page() with a page that's
not on an LRU list.  Both anonymous and page cache pages should be on
an LRU list.  What am I missing?