linux-kernel - Re: a question of split_huge

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Message-ID: <20200709160750.utl46xvavceuvnom@box>
Date:   Thu, 9 Jul 2020 19:07:50 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Alex Shi <alex.shi@...ux.alibaba.com>,
        Johannes Weiner <hannes@...xchg.org>,
        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 04:50:02PM +0100, Matthew Wilcox wrote:
> 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?

Right, and it's never got removed from LRU during the split. The tail
pages have to be added to LRU because they now separate from the tail
page.

-- 
 Kirill A. Shutemov