linux-kernel - Re: [PATCH 19/36] autonuma: memory follows CPU algorithm and task/mm

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Date:	Wed, 22 Aug 2012 14:22:33 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Andi Kleen <andi@...stfloor.org>
cc:	Andrea Arcangeli <aarcange@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 19/36] autonuma: memory follows CPU algorithm and
 task/mm_autonuma stats collection

On Wed, 22 Aug 2012, Andi Kleen wrote:
> Andrea Arcangeli <aarcange@...hat.com> writes:
> > +		/*
> > +		 * Take the lock with irqs disabled to avoid a lock
> > +		 * inversion with the lru_lock. The lru_lock is taken
> > +		 * before the autonuma_migrate_lock in
> > +		 * split_huge_page. If we didn't disable irqs, the
> > +		 * lru_lock could be taken by interrupts after we have
> > +		 * obtained the autonuma_migrate_lock here.
> > +		 */
> 
> Which interrupt code takes the lru_lock? That sounds like a bug.

Not a bug: the clearest example is end_page_writeback() calling
rotate_reclaimable_page(); but I think once you probe deeper, you
find some other mm/swap.c pagevec operations which may get called
from interrupt, and end up freeing unrelated PageLRU pages.

Hugh
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