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From:   Jason Gunthorpe <jgg@mellanox.com>
To:     Christoph Hellwig <hch@lst.de>
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Subject: Re: [PATCH 01/10] mm: turn migrate_vma upside down
Thread-Topic: [PATCH 01/10] mm: turn migrate_vma upside down
Thread-Index: AQHVUnY4TvdvZdqG70SoVm3XhXkEbab+BjuAgAEzdgCAABX0AA==
Date:   Sat, 17 Aug 2019 12:50:06 +0000
Message-ID: <20190817125002.GB10068@mellanox.com>
References: <20190814075928.23766-1-hch@lst.de>
 <20190814075928.23766-2-hch@lst.de> <20190816171101.GK5412@mellanox.com>
 <20190817113128.GA23295@lst.de>
In-Reply-To: <20190817113128.GA23295@lst.de>
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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);
>=20
> 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