linux-kernel - Re: [PATCH v3 1/3] mm: document zone device struct page field usage

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Message-ID: <20190725012225.GB32003@mellanox.com>
Date:   Thu, 25 Jul 2019 01:22:29 +0000
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Ralph Campbell <rcampbell@...dia.com>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        John Hubbard <jhubbard@...dia.com>,
        Matthew Wilcox <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>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v3 1/3] mm: document zone device struct page field usage

On Wed, Jul 24, 2019 at 04:26:58PM -0700, Ralph Campbell wrote:
> Struct page for ZONE_DEVICE private pages uses the page->mapping and
> and page->index fields while the source anonymous pages are migrated to
> device private memory. This is so rmap_walk() can find the page when
> migrating the ZONE_DEVICE private page back to system memory.
> ZONE_DEVICE pmem backed fsdax pages also use the page->mapping and
> page->index fields when files are mapped into a process address space.
> 
> Add comments to struct page and remove the unused "_zd_pad_1" field
> to make this more clear.
> 
> Signed-off-by: Ralph Campbell <rcampbell@...dia.com>
> Reviewed-by: John Hubbard <jhubbard@...dia.com>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Jérôme Glisse <jglisse@...hat.com>
> Cc: "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
> Cc: Lai Jiangshan <jiangshanlai@...il.com>
> Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
> Cc: Pekka Enberg <penberg@...nel.org>
> Cc: Randy Dunlap <rdunlap@...radead.org>
> Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Jason Gunthorpe <jgg@...lanox.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>  include/linux/mm_types.h | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)

Ralph, you marked some of thes patches as mm/hmm, but I feel it is
best if Andrew takes them through the normal -mm path.

They don't touch hmm.c or mmu notifiers so I don't forsee conflicts,
and I don't feel comfortable to review this code.

Regards,
Jason