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Date:   Wed, 3 Feb 2021 14:00:04 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Joao Martins <joao.m.martins@oracle.com>
Cc:     Pavel Tatashin <pasha.tatashin@soleen.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
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Subject: Re: [PATCH v8 02/14] mm/gup: check every subpage of a compound page
 during isolation
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On Wed, Feb 03, 2021 at 04:13:21PM +0000, Joao Martins wrote:

> If check_and_migrate_movable_pages() is meant to migrate unpinned
> pages, then rather than pinning+unpinning+moving, perhaps it would
> be called in __get_user_pages() place where we are walking page
> tables and know if it's a PUD/PMD and can skip all the subpages and
> just record and migrate those instead. Was that your thinking?

I think a reasonable approach is to detect non-pinnable pages while
walking the VMAs, when found isolate them and thread them on a linked
list.

When the VMA walk is done you'll have a linked list of isolated pages
that need migration. So the check_and_migrate_movable_pages() gets
split into the top half being diffused in the VMA walk and the bottom
half still called after __get_user_pages() returns.

Jason