linux-kernel - Re: [PATCH] mm: introduce MADV_CLR

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Message-ID: <20170531141939.GP27783@dhcp22.suse.cz>
Date:   Wed, 31 May 2017 16:19:40 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Mike Rapoprt <rppt@...ux.vnet.ibm.com>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        linux-mm <linux-mm@...ck.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE

On Wed 31-05-17 15:39:22, Mike Rapoprt wrote:
> 
> 
> On May 31, 2017 3:08:22 PM GMT+03:00, Michal Hocko <mhocko@...nel.org> wrote:
[...]
> > From what Mike said a global disable THP for the whole process
> >while the post-copy is in progress is a better solution anyway.
> 
> For the CRIU usecase, disabling THP for a while and re-enabling
> it back will do the trick, provided VMAs flags are not affected,
> like in the patch you've sent.  Moreover, we may even get away with
> ioctl(UFFDIO_COPY) if it's overhead shows to be negligible.  Still,
> I believe that MADV_RESET_HUGEPAGE (or some better named) command has
> the value on its own.

I would prefer if we could go the prctl if possible and add a new
MADV_RESET_HUGEPAGE if there is really a usecase for it.
-- 
Michal Hocko
SUSE Labs