linux-kernel - Re: [PATCH 1/3] mm, numa: rework do_pages

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Date:   Fri, 5 Jan 2018 19:09:05 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Christopher Lameter <cl@...ux.com>
Cc:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Zi Yan <zi.yan@...rutgers.edu>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrea Reale <ar@...ux.vnet.ibm.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] mm, numa: rework do_pages_move

On Fri 05-01-18 11:15:18, Cristopher Lameter wrote:
> On Fri, 5 Jan 2018, Michal Hocko wrote:
> 
> > Yes. I am really wondering because there souldn't anything specific to
> > improve the situation with patch 2 and 3. Likewise the only overhead
> > from the patch 1 I can see is the reduced batching of the mmap_sem. But
> > then I am wondering what would compensate that later...
> 
> Could you reduce the frequency of taking mmap_sem? Maybe take it when
> picking a new node and drop it when done with that node before migrating
> the list of pages?

I believe there should be some cap on the number of pages. We shouldn't
keep it held for million of pages if all of them are moved to the same
node. I would really like to postpone that to later unless it causes
some noticeable regressions because this would complicate the code
further and I am not sure this is all worth it.

-- 
Michal Hocko
SUSE Labs