linux-kernel - Re: [PATCH -v3 07/10] mm, THP, swap: Support to add/delete THP to/from swap cache

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Message-Id: <57D128A9.3030306@linux.vnet.ibm.com>
Date:   Thu, 08 Sep 2016 14:30:25 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     "Huang, Ying" <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     tim.c.chen@...el.com, dave.hansen@...el.com, andi.kleen@...el.com,
        aaron.lu@...el.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
        Shaohua Li <shli@...nel.org>, Minchan Kim <minchan@...nel.org>,
        Rik van Riel <riel@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH -v3 07/10] mm, THP, swap: Support to add/delete THP to/from
 swap cache

On 09/07/2016 10:16 PM, Huang, Ying wrote:
> From: Huang Ying <ying.huang@...el.com>
> 
> With this patch, a THP (Transparent Huge Page) can be added/deleted
> to/from the swap cache as a set of sub-pages (512 on x86_64).
> 
> This will be used for the THP (Transparent Huge Page) swap support.
> Where one THP may be added/delted to/from the swap cache.  This will
> batch the swap cache operations to reduce the lock acquire/release times
> for the THP swap too.
> 
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: Shaohua Li <shli@...nel.org>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> ---
>  include/linux/page-flags.h |  2 +-
>  mm/swap_state.c            | 57 +++++++++++++++++++++++++++++++---------------
>  2 files changed, 40 insertions(+), 19 deletions(-)
> 
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 74e4dda..f5bcbea 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -314,7 +314,7 @@ PAGEFLAG_FALSE(HighMem)
>  #endif
>  
>  #ifdef CONFIG_SWAP
> -PAGEFLAG(SwapCache, swapcache, PF_NO_COMPOUND)
> +PAGEFLAG(SwapCache, swapcache, PF_NO_TAIL)

What is the reason for this change ? The commit message does not seem
to explain.