linux-kernel - Re: [patch for-5.3 0/4] revert immediate fallback to remote hugepages

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Date:   Mon, 25 Nov 2019 12:47:08 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Mel Gorman <mgorman@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [patch for-5.3 0/4] revert immediate fallback to remote hugepages

On Sun 24-11-19 16:10:53, David Rientjes wrote:
[...]
> So my question would be: if we know the previous behavior that allowed 
> excessive swap and recalling into compaction was deemed harmful for the 
> local node, why do we now believe it cannot be harmful if done for all 
> system memory?

I have to say that I got lost in your explanation. I have already
pointed this out in a previous email you didn't reply to. But the main
difference to previous __GFP_THISNODE behavior is that it is used along
with __GFP_NORETRY and that reduces the overall effort of the reclaim
AFAIU. If that is not the case then please be _explicit_ why.

Having test results from Andrea would be really appreciated of course
but he seems to be too busy to do that (or maybe not interested
anymore). I do not see any real reason to hold on this patch based on
hand waving though. So either we have some good reasoning to argue
against the patch or a good testing results or we should go ahead.
As things stand right now, THP success rate went down after your last
changes for _very simple_ workloads. This needs addressing which I hope
we do agree on.
-- 
Michal Hocko
SUSE Labs