linux-kernel - Re: [PATCH 1/2] mm: fix bogus VM_BUG_ON_PAGE() in isolate_lru

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Date:	Mon, 1 Feb 2016 15:24:46 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	David Rientjes <rientjes@...gle.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: fix bogus VM_BUG_ON_PAGE() in isolate_lru_page()

On Mon 01-02-16 16:26:08, Kirill A. Shutemov wrote:
> We don't care if there's a tail pages which is not on LRU. We are not
> going to isolate them anyway.

yes we are not going to isolate them but calling this function on a
tail page is wrong in principle, no? PageLRU check is racy outside of
lru_lock so what if we are racing here. I know, highly unlikely but not
impossible. So I am not really sure this is an improvement. When would
we hit this VM_BUG_ON and it wouldn't be a bug or at least suspicious
usage?
-- 
Michal Hocko
SUSE Labs