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Date: Sun, 4 Feb 2024 18:51:05 +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 1/2] mm: pgtable: add missing flag and statistics for
 kernel PTE page
Message-ID: <Zb_cmZByel4cULDP@casper.infradead.org>
References: <f023a6687b9f2109401e7522b727aa4708dc05f1.1706774109.git.zhengqi.arch@bytedance.com>
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In-Reply-To: <f023a6687b9f2109401e7522b727aa4708dc05f1.1706774109.git.zhengqi.arch@bytedance.com>

On Thu, Feb 01, 2024 at 04:05:40PM +0800, Qi Zheng wrote:
> For kernel PTE page, we do not need to allocate and initialize its split
> ptlock, but as a page table page, it's still necessary to add PG_table
> flag and NR_PAGETABLE statistics for it.

No, this is wrong.

We do not account _kernel_ page tables to the _user_.  Just because
the kernel, say, called vmalloc() doesn't mean we should charge the
task for it.  Moreover, one task may call vmalloc() and a different task
would then call vfree().

This is a can of worms you don't want to open.  Why did you want to do
this?