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Date: Thu, 11 Apr 2024 00:59:09 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Peter Xu <peterx@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Suren Baghdasaryan <surenb@google.com>,
	Lokesh Gidra <lokeshgidra@google.com>,
	"Liam R . Howlett" <Liam.Howlett@oracle.com>,
	Alistair Popple <apopple@nvidia.com>
Subject: Re: [PATCH] mm: Always sanity check anon_vma first for per-vma locks
Message-ID: <ZhcnzS1S6zOMJwSL@casper.infradead.org>
References: <20240410170621.2011171-1-peterx@redhat.com>
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On Wed, Apr 10, 2024 at 05:23:18PM -0400, Peter Xu wrote:
> On Wed, Apr 10, 2024 at 10:10:45PM +0100, Matthew Wilcox wrote:
> > > I can do some tests later today or tomorrow. Any suggestion you have on
> > > amplifying such effect that you have concern with?
> > 
> > 8 socket NUMA system, 800MB text segment, 10,000 threads.  No, I'm not
> > joking, that's a real customer workload.
> 
> Well, I believe you, but even with this, that's a total of 800MB memory on
> a giant moster system... probably just to fault in once.
> 
> And even before we talk about that into details.. we're talking about such
> giant program running acorss hundreds of cores with hundreds of MB text,
> then... hasn't the program developer already considered mlockall() at the
> entry of the program?  Wouldn't that greatly beneficial already with
> whatever granule of locks that a future fault would take?

I don't care what your theory is, or even what your benchmarking shows.
I had basically the inverse of this patch, and my customer's workload
showed significant improvement as a result.  Data talks, bullshit walks.
Your patch is NAKed and will remain NAKed.