linux-kernel - Re: [v2 PATCH 7/7] mm: thp: skip make PMD PROT

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Message-ID: <20210517153044.GZ3672@suse.de>
Date:   Mon, 17 May 2021 16:30:44 +0100
From:   Mel Gorman <mgorman@...e.de>
To:     Yang Shi <shy828301@...il.com>
Cc:     kirill.shutemov@...ux.intel.com, ziy@...dia.com, mhocko@...e.com,
        ying.huang@...el.com, hughd@...gle.com,
        gerald.schaefer@...ux.ibm.com, hca@...ux.ibm.com,
        gor@...ux.ibm.com, borntraeger@...ibm.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH 7/7] mm: thp: skip make PMD PROT_NONE if THP migration
 is not supported

On Tue, Apr 13, 2021 at 02:24:16PM -0700, Yang Shi wrote:
> A quick grep shows x86_64, PowerPC (book3s), ARM64 and S390 support both
> NUMA balancing and THP.  But S390 doesn't support THP migration so NUMA
> balancing actually can't migrate any misplaced pages.
> 
> Skip make PMD PROT_NONE for such case otherwise CPU cycles may be wasted
> by pointless NUMA hinting faults on S390.
> 
> Signed-off-by: Yang Shi <shy828301@...il.com>

Acked-by: Mel Gorman <mgorman@...e.de>

-- 
Mel Gorman
SUSE Labs