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

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Date:   Tue, 5 Nov 2019 17:01:00 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        "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 Tue, 5 Nov 2019, Michal Hocko wrote:

> > > Thanks, I'll queue this for some more testing.  At some point we should
> > > decide on a suitable set of Fixes: tags and a backporting strategy, if any?
> > > 
> > 
> > I'd strongly suggest that Andrea test this patch out on his workload on 
> > hosts where all nodes are low on memory because based on my understanding 
> > of his reported issue this would result in swap storms reemerging but 
> > worse this time because they wouldn't be constrained only locally.  (This 
> > patch causes us to no longer circumvent excessive reclaim when using 
> > MADV_HUGEPAGE.)
> 
> Could you be more specific on why this would be the case? My testing is
> doesn't show any such signs and I am effectivelly testing memory low
> situation. The amount of reclaimed memory matches the amount of
> requested memory.
> 

The follow-up allocation in alloc_pages_vma() would no longer use 
__GFP_NORETRY and there is no special handling to avoid swap storms in the 
page allocator anymore as a result of this patch.  I don't see any 
indication that this allocation would behave any different than the code 
that Andrea experienced swap storms with, but now worse if remote memory 
is in the same state local memory is when he's using __GFP_THISNODE.