linux-kernel - Re: [PATCH] doc: mm: migration doesn't use FOLL

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Message-ID: <C8CBF3A3-5ADA-4CA6-8AEB-4836AE9146D7@nvidia.com>
Date:   Thu, 18 Apr 2019 16:30:27 -0400
From:   Zi Yan <ziy@...dia.com>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
CC:     <mhocko@...e.com>, <kirill.shutemov@...ux.intel.com>,
        <rppt@...ux.vnet.ibm.com>, <corbet@....net>,
        <akpm@...ux-foundation.org>, <linux-doc@...r.kernel.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] doc: mm: migration doesn't use FOLL_SPLIT anymore

On 18 Apr 2019, at 16:17, Yang Shi wrote:

> When demonstrating FOLL_SPLIT in transhuge document, migration is used
> as an example.  But, since commit 94723aafb9e7 ("mm: unclutter THP
> migration"), the way of THP migration is totally changed.  FOLL_SPLIT 
> is
> not used by migration anymore due to the change.
>
> Remove the obsolete example to avoid confusion.
>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Zi Yan <ziy@...dia.com>
> Cc: Mike Rapoport <rppt@...ux.vnet.ibm.com>
> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
> ---
>  Documentation/vm/transhuge.rst | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
>
> diff --git a/Documentation/vm/transhuge.rst 
> b/Documentation/vm/transhuge.rst
> index a8cf680..8df3806 100644
> --- a/Documentation/vm/transhuge.rst
> +++ b/Documentation/vm/transhuge.rst
> @@ -55,13 +55,7 @@ prevent page from being split by anyone.
>  In case you can't handle compound pages if they're returned by
>  follow_page, the FOLL_SPLIT bit can be specified as parameter to
>  follow_page, so that it will split the hugepages before returning
> -them. Migration for example passes FOLL_SPLIT as parameter to
> -follow_page because it's not hugepage aware and in fact it can't work
> -at all on hugetlbfs (but it instead works fine on transparent
> -hugepages thanks to FOLL_SPLIT). migration simply can't deal with
> -hugepages being returned (as it's not only checking the pfn of the
> -page and pinning it during the copy but it pretends to migrate the
> -memory in regular page sizes and with regular pte/pmd mappings).
> +them.
>
>  Graceful fallback
>  =================
> -- 
> 1.8.3.1

Thanks for updating the document.

Reviewed-by: Zi Yan <ziy@...dia.com>



--
Best Regards,
Yan Zi