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

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Message-ID: <20161230140839.qg3maz4ifyf7nwgq@techsingularity.net>
Date:   Fri, 30 Dec 2016 14:08:39 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     David Rientjes <rientjes@...gle.com>,
        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 Fri, Dec 30, 2016 at 01:56:16PM +0100, Michal Hocko wrote:
> On Fri 30-12-16 12:36:20, Mel Gorman wrote:
> [...]
> > I'll neither ack nor nak this patch. However, I would much prefer an
> > additional option be added to sysfs called defer-fault that would avoid
> > all fault-based stalls but still potentially stall for MADV_HUGEPAGE.
> 
> Would you consider changing the semantic of defer=madvise to invoke
> KSWAPD for !madvised vmas as acceptable. It would be a change in
> semantic but I am wondering what would be a risk and potential
> regression space.
> 

I'd worry a little, but not a lot. The concern would be that kswapd waking
up would reclaim pages and cause major faults that would have remained
resident with the current semantics.

-- 
Mel Gorman
SUSE Labs