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Message-ID: <87fu2lkc7d.fsf@yhuang-dev.intel.com>
Date: Mon, 21 May 2018 09:51:50 +0800
From: "Huang\, Ying" <ying.huang@...el.com>
To: Michal Hocko <mhocko@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
<linux-kernel@...r.kernel.org>, Andi Kleen <andi.kleen@...el.com>,
Jan Kara <jack@...e.cz>,
Andrea Arcangeli <aarcange@...hat.com>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Matthew Wilcox <mawilcox@...rosoft.com>,
Hugh Dickins <hughd@...gle.com>,
Minchan Kim <minchan@...nel.org>, Shaohua Li <shli@...com>,
Christopher Lameter <cl@...ux.com>,
Mike Kravetz <mike.kravetz@...cle.com>
Subject: Re: [PATCH -mm] mm, huge page: Copy to access sub-page last when copy huge page
Hi, Michal,
Michal Hocko <mhocko@...nel.org> writes:
> On Fri 18-05-18 11:03:16, Huang, Ying wrote:
> [...]
>> The patch is a generic optimization which should benefit quite some
>> workloads, not for a specific use case. To demonstrate the performance
>> benefit of the patch, we tested it with vm-scalability run on
>> transparent huge page.
>
> It is also adds quite some non-intuitive code. So is this worth? Does
> any _real_ workload benefits from the change?
I don't have any _real_ workload which benefits from this. But I think
this is the right way to copy the huge page. It should benefit many
workloads with heavy cache contention, as illustrated in the
micro-benchmark. But the performance benefit may be small or
non-measurable for the _real_ workload.
The code does become not as intuitive as before. But fortunately, all
non-intuitive code are in copy_user_huge_page(), which is a leaf
function with well defined interface and semantics. And with the help
of the code comments, at least the intention of the code is clear.
Best Regards,
Huang, Ying
>> include/linux/mm.h | 3 ++-
>> mm/huge_memory.c | 3 ++-
>> mm/memory.c | 43 +++++++++++++++++++++++++++++++++++++++----
>> 3 files changed, 43 insertions(+), 6 deletions(-)
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