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Message-ID: <20181205011519.GV10377@bombadil.infradead.org>
Date: Tue, 4 Dec 2018 17:15:19 -0800
From: Matthew Wilcox <willy@...radead.org>
To: John Hubbard <jhubbard@...dia.com>
Cc: Dan Williams <dan.j.williams@...el.com>,
John Hubbard <john.hubbard@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux MM <linux-mm@...ck.org>, Jan Kara <jack@...e.cz>,
tom@...pey.com, Al Viro <viro@...iv.linux.org.uk>, benve@...co.com,
Christoph Hellwig <hch@...radead.org>,
Christopher Lameter <cl@...ux.com>,
"Dalessandro, Dennis" <dennis.dalessandro@...el.com>,
Doug Ledford <dledford@...hat.com>,
Jason Gunthorpe <jgg@...pe.ca>,
Jérôme Glisse <jglisse@...hat.com>,
Michal Hocko <mhocko@...nel.org>, mike.marciniszyn@...el.com,
rcampbell@...dia.com,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions
On Tue, Dec 04, 2018 at 04:58:01PM -0800, John Hubbard wrote:
> On 12/4/18 3:03 PM, Dan Williams wrote:
> > Except the LRU fields are already in use for ZONE_DEVICE pages... how
> > does this proposal interact with those?
>
> Very badly: page->pgmap and page->hmm_data both get corrupted. Is there an entire
> use case I'm missing: calling get_user_pages() on ZONE_DEVICE pages? Said another
> way: is it reasonable to disallow calling get_user_pages() on ZONE_DEVICE pages?
>
> If we have to support get_user_pages() on ZONE_DEVICE pages, then the whole
> LRU field approach is unusable.
We just need to rearrange ZONE_DEVICE pages. Please excuse the whitespace
damage:
+++ b/include/linux/mm_types.h
@@ -151,10 +151,12 @@ struct page {
#endif
};
struct { /* ZONE_DEVICE pages */
+ unsigned long _zd_pad_2; /* LRU */
+ unsigned long _zd_pad_3; /* LRU */
+ unsigned long _zd_pad_1; /* uses mapping */
/** @pgmap: Points to the hosting device page map. */
struct dev_pagemap *pgmap;
unsigned long hmm_data;
- unsigned long _zd_pad_1; /* uses mapping */
};
/** @rcu_head: You can use this to free a page by RCU. */
You don't use page->private or page->index, do you Dan?
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