From: Qi Zheng <zhengqi.arch@bytedance.com>
To: Matthew Wilcox <willy@infradead.org>
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
Date: Mon, 5 Feb 2024 10:14:28 +0800 [thread overview]
Message-ID: <d464ef84-fe06-4279-a7fb-5a0cadef4064@bytedance.com> (raw)
In-Reply-To: <Zb_dT43-oPsRplhi@casper.infradead.org>
Hi Matthew,
On 2024/2/5 02:54, Matthew Wilcox wrote:
> 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.
The reason I first noticed this is that we didn't allocate and
initialize the ptlock in __pte_alloc_one_kernel(). So in at the PTE
level, the implementation of kernel & user page tables is already
different.
Thanks.
next prev parent reply other threads:[~2024-02-05 2:14 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-01 8:05 [PATCH 1/2] mm: pgtable: add missing flag and statistics for kernel PTE page Qi Zheng
2024-02-01 8:05 ` [PATCH 2/2] mm: pgtable: remove unnecessary split ptlock for kernel PMD page Qi Zheng
2024-02-02 3:16 ` Muchun Song
2024-02-04 18:54 ` Matthew Wilcox
2024-02-05 2:14 ` Qi Zheng [this message]
2024-02-02 2:47 ` [PATCH 1/2] mm: pgtable: add missing flag and statistics for kernel PTE page Muchun Song
2024-02-04 10:58 ` Mike Rapoport
2024-02-04 11:39 ` Qi Zheng
2024-02-04 12:15 ` Mike Rapoport
2024-02-04 16:26 ` Qi Zheng
2024-02-04 18:51 ` Matthew Wilcox
2024-02-05 2:05 ` Qi Zheng
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