linux-kernel - Re: [PATCH 1/3] mm: document zone device struct page reserved fields

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Message-ID: <4295112b-e5ff-f9ad-defc-597ad3bc49a1@nvidia.com>
Date:   Wed, 17 Jul 2019 10:50:20 -0700
From:   Ralph Campbell <rcampbell@...dia.com>
To:     Christoph Hellwig <hch@....de>, John Hubbard <jhubbard@...dia.com>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <willy@...radead.org>, Vlastimil Babka <vbabka@...e.cz>,
        Christoph Lameter <cl@...ux.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Pekka Enberg <penberg@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/3] mm: document zone device struct page reserved fields


On 7/16/19 9:38 PM, Christoph Hellwig wrote:
> On Tue, Jul 16, 2019 at 09:31:33PM -0700, John Hubbard wrote:
>> OK, so just delete all the _zd_pad_* fields? Works for me. It's misleading to
>> calling something padding, if it's actually unavailable because it's used
>> in the other union, so deleting would be even better than commenting.
>>
>> In that case, it would still be nice to have this new snippet, right?:
> 
> I hope willy can chime in a bit on his thoughts about how the union in
> struct page should look like.  The padding at the end of the sub-structs
> certainly looks pointless, and other places don't use it either.  But if
> we are using the other fields it almost seems to me like we only want to
> union the lru field in the first sub-struct instead of overlaying most
> of it.
>

I like this approach.
I'll work on an updated patch that makes "struct list_head lru" part
of a union with the ZONE_DEVICE struct without the padding and update
the comments and change log.

I will also wait a day or two for others to add their comments.