linux-kernel - Re: [patch] mm, thp: always direct reclaim for MADV

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Message-ID: <alpine.DEB.2.10.1701041348580.77987@chino.kir.corp.google.com>
Date:   Wed, 4 Jan 2017 13:53:16 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
cc:     Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [patch] mm, thp: always direct reclaim for MADV_HUGEPAGE even
 when deferred

On Wed, 4 Jan 2017, Mel Gorman wrote:

> There is a slight disconnect. The bug reports I'm aware of predate the
> introduction of "defer" and the current "madvise" semantics for defrag. The
> current semantics have not had enough time in the field to generate
> reports. I expect lag before users are aware of "defer" due to the number
> of recommendations out there about blindly disabling THP.  This because
> the majority of users I deal with are not running mainline kernels.
> 

I find it sad that we need to have five options for thp defrag and that 
people now need to research options that don't break their userspace and 
affect all applications on the system, especially when one of those 
options now appears to have a hypothetical usecase, but in the interest of 
making forward progress in this area for support that we truly need, I'll 
reluctantly propose it as a patch.