linux-kernel - Re: [PATCH -mm] mm, huge page: Copy to access sub-page last when copy huge page

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Message-ID: <64430ed4-4019-d597-ccb3-8bf6b04ee464@oracle.com>
Date:   Fri, 18 May 2018 09:41:04 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Michal Hocko <mhocko@...nel.org>,
        "Huang, Ying" <ying.huang@...el.com>
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>
Subject: Re: [PATCH -mm] mm, huge page: Copy to access sub-page last when copy
 huge page

On 05/17/2018 11:24 PM, Michal Hocko wrote:
> 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?

One way to 'add less code' would be to create a helper routine that
indicates the order in which sub-pages are to be copied.  IIUC, you
added the same algorithm for sub-page ordering to copy_huge_page()
that was previously added to clear_huge_page().  Correct?  If so,
then perhaps a common helper could be used by both the clear and copy
huge page routines.  It would also make maintenance easier.

-- 
Mike Kravetz