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

[Randy Dunlap]

On 04/16/18 19:02, Huang, Ying wrote:
> From: Huang Ying <ying.huang@xxxxxxxxx>
> 
> 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.

> 
> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Shaohua Li <shli@xxxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Cc: Zi Yan <zi.yan@xxxxxxxxxxxxxx>
> ---
>  include/linux/swap.h |  6 +++++
>  mm/huge_memory.c     | 54 ++++++++++++++++++++++++++++++++++++++++----
>  mm/swapfile.c        | 28 +++++++++++++++++++++++
>  3 files changed, 83 insertions(+), 5 deletions(-)


-- 
~Randy