linux-kernel - Re: [PATCH -mm 06/21] mm, THP, swap: Support PMD swap mapping when splitting huge PMD

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Date:   Wed, 18 Apr 2018 08:38:16 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...el.com>,
        Andi Kleen <ak@...ux.intel.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        "Shaohua Li" <shli@...nel.org>, Hugh Dickins <hughd@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Rik van Riel <riel@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Zi Yan <zi.yan@...rutgers.edu>
Subject: Re: [PATCH -mm 06/21] mm, THP, swap: Support PMD swap mapping when splitting huge PMD

Randy Dunlap <rdunlap@...radead.org> writes:

> On 04/16/18 19:02, Huang, Ying wrote:
>> From: Huang Ying <ying.huang@...el.com>
>> 
>> A huge PMD need to be split when zap a part of the PMD mapping etc.
>> If the PMD mapping is a swap mapping, we need to split it too.  This
>> patch implemented the support for this.  This is similar as splitting
>> the PMD page mapping, except we need to decrease the PMD swap mapping
>> count for the huge swap cluster too.  If the PMD swap mapping count
>> becomes 0, the huge swap cluster will be split.
>> 
>> Notice: is_huge_zero_pmd() and pmd_page() doesn't work well with swap
>> PMD, so pmd_present() check is called before them.
>
> FWIW, I would prefer to see that comment in the source code, not just
> in the commit description.

Sure.  I will add comment in source code too.

Best Regards,
Huang, Ying

>> 
>> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
>> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
>> Cc: Andrea Arcangeli <aarcange@...hat.com>
>> Cc: Michal Hocko <mhocko@...e.com>
>> Cc: Johannes Weiner <hannes@...xchg.org>
>> Cc: Shaohua Li <shli@...nel.org>
>> Cc: Hugh Dickins <hughd@...gle.com>
>> Cc: Minchan Kim <minchan@...nel.org>
>> Cc: Rik van Riel <riel@...hat.com>
>> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
>> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
>> Cc: Zi Yan <zi.yan@...rutgers.edu>
>> ---
>>  include/linux/swap.h |  6 +++++
>>  mm/huge_memory.c     | 54 ++++++++++++++++++++++++++++++++++++++++----
>>  mm/swapfile.c        | 28 +++++++++++++++++++++++
>>  3 files changed, 83 insertions(+), 5 deletions(-)