linux-kernel - Re: [PATCH 1/2] mm: pgtable: add missing flag and statistics for kernel PTE page

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Message-ID: <Zb_cmZByel4cULDP@casper.infradead.org>
Date: Sun, 4 Feb 2024 18:51:05 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Qi Zheng <zhengqi.arch@...edance.com>
Cc: akpm@...ux-foundation.org, arnd@...db.de, muchun.song@...ux.dev,
	david@...hat.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: pgtable: add missing flag and statistics for
 kernel PTE page

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?