linux-kernel - Re: [PATCH] mm-move-mremap-from-file_operations-to-vm_operations

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Date:	Mon, 20 Jul 2015 22:03:58 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Benjamin LaHaise <bcrl@...ck.org>
Cc:	Jeff Moyer <jmoyer@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <js1304@...il.com>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH]
	mm-move-mremap-from-file_operations-to-vm_operations_struct-fix

On 07/20, Benjamin LaHaise wrote:
>
> On Mon, Jul 20, 2015 at 09:24:40PM +0200, Oleg Nesterov wrote:
> > On 07/20, Oleg Nesterov wrote:
> > >
> > > But again, again, please ignore. This all is off-topic and my understanding
> > > is very limited.
> >
> > Yes, yes, but sorry for noise and let me repeat...
> >
> > This memory lives in page-cache/lru, it is visible for shrinker which
> > will unmap these pages for no reason on memory shortage. IOW, aio fools
> > the kernel, this memory looks reclaimable but it is not. And we only do
> > this for migration.
>
> And we have the same problem with O_DIRECT.

I don't this so, or I misunderstood. Sure, dio_get_page() will pin the page.
But not forever and this is unavoidable. This is not the same. OK, nevermind,
lets forget this.

> > And I should have changes the subject a long ago... So what do you think
> > we should do with the build failure?
>
> I honestly don't care what of the options you do -- please just don't go
> about adding BUG()s.

OK, thanks.

Then I'll send v2 which adds ifdef(MMU) into aio_ring_vm_ops tomorrow.

Oleg.

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