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Date: Sun, 4 Feb 2024 18:54:07 +0000
From: Matthew Wilcox <willy@infradead.org>
To: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: akpm@linux-foundation.org, arnd@arndb.de, muchun.song@linux.dev,
	david@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	linux-arch@vger.kernel.org
Subject: Re: [PATCH 2/2] mm: pgtable: remove unnecessary split ptlock for
 kernel PMD page
Message-ID: <Zb_dT43-oPsRplhi@casper.infradead.org>
References: <f023a6687b9f2109401e7522b727aa4708dc05f1.1706774109.git.zhengqi.arch@bytedance.com>
 <63f0b3d2f9124ae5076963fb5505bd36daba0393.1706774109.git.zhengqi.arch@bytedance.com>
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On Thu, Feb 01, 2024 at 04:05:41PM +0800, Qi Zheng wrote:
> For kernel PMD entry, we use init_mm.page_table_lock to protect it, so
> there is no need to allocate and initialize the split ptlock for kernel
> PMD page.

I don't think this is a great idea.  Maybe there's no need to initialise
it, but keeping things the same between kernel & user page tables is a
usually better.  We don't normally allocate memory for the spinlock,
it's only in debugging scenarios like LOCKDEP.  I would drop this unless
you have a really compelling argument to make.