linux-kernel - Re: [PATCH 01/10] mm: turn migrate

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Message-ID: <20190817125002.GB10068@mellanox.com>
Date:   Sat, 17 Aug 2019 12:50:06 +0000
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Christoph Hellwig <hch@....de>
CC:     Jérôme Glisse <jglisse@...hat.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Bharata B Rao <bharata@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/10] mm: turn migrate_vma upside down

On Sat, Aug 17, 2019 at 01:31:28PM +0200, Christoph Hellwig wrote:
> On Fri, Aug 16, 2019 at 05:11:07PM +0000, Jason Gunthorpe wrote:
> > -	if (args->cpages)
> > -		migrate_vma_prepare(args);
> > -	if (args->cpages)
> > -		migrate_vma_unmap(args);
> > +	if (!args->cpages)
> > +		return 0;
> > +
> > +	migrate_vma_prepare(args);
> > +	migrate_vma_unmap(args);
> 
> I don't think this is ok.  Both migrate_vma_prepare and migrate_vma_unmap
> can reduce args->cpages, including possibly to 0.

Oh, yes, that was far too hasty on my part, I had assumed collect set
the cpages. Thank you for checking

Jason