linux-kernel - Re: [PATCH] mm: Always sanity check anon

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Message-ID: <ZhhaRXHKk7w_hKgi@x1n>
Date: Thu, 11 Apr 2024 17:46:45 -0400
From: Peter Xu <peterx@...hat.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Lokesh Gidra <lokeshgidra@...gle.com>,
	Alistair Popple <apopple@...dia.com>
Subject: Re: [PATCH] mm: Always sanity check anon_vma first for per-vma locks

On Thu, Apr 11, 2024 at 10:27:56PM +0100, Matthew Wilcox wrote:
> On Thu, Apr 11, 2024 at 05:12:02PM -0400, Peter Xu wrote:
> > The question is whether that's intended to make it as complicated.  For
> > example, why don't we check anon_vma for anonymous too later when prepare
> > anon_vma, however we do it late for file memory.  AFAICT there's nothing
> > special with file memory in this case.
> 
> Yes, it's absolutely intended.  If anything, anon memory is the special
> case that checks up-front.
> 
> Congratulations on adding additional instructions to the common case.
> I don't understand why you persist with your nonsense.  Please stop.

How many instructions it takes for a late RETRY for WRITEs to private file
mappings, fallback to mmap_sem?

Did you even finish reading the patch at all?

-- 
Peter Xu