linux-kernel - Re: [PATCH v5 6/8] mm: Introduce deferred freeing for kernel page tables

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Message-ID: <7a001cb9-fb09-487c-bfa9-e2d329b0f6a8@linux.intel.com>
Date: Sat, 11 Oct 2025 14:30:54 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: David Hildenbrand <david@...hat.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Kevin Tian <kevin.tian@...el.com>, Jason Gunthorpe <jgg@...dia.com>,
 Jann Horn <jannh@...gle.com>, Vasant Hegde <vasant.hegde@....com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...el.com>,
 Alistair Popple <apopple@...dia.com>, Peter Zijlstra <peterz@...radead.org>,
 Uladzislau Rezki <urezki@...il.com>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Andy Lutomirski <luto@...nel.org>, Yi Lai <yi1.lai@...el.com>
Cc: iommu@...ts.linux.dev, security@...nel.org, x86@...nel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v5 6/8] mm: Introduce deferred freeing for kernel page
 tables

On 10/10/25 23:47, David Hildenbrand wrote:
> On 19.09.25 07:40, Lu Baolu wrote:
>> From: Dave Hansen <dave.hansen@...ux.intel.com>
>>
>> This introduces a conditional asynchronous mechanism, enabled by
>> CONFIG_ASYNC_PGTABLE_FREE. When enabled, this mechanism defers the 
>> freeing
>> of pages that are used as page tables for kernel address mappings. These
>> pages are now queued to a work struct instead of being freed immediately.
>>
> 
> Okay, I now looked at patch #8 and I think the whole reason of this 
> patch is "batch-free page tables to minimize the impact of an expensive 
> cross-page table operation" which is a single TLB flush.
> 
>> This deferred freeing provides a safe context for a future patch to add
> 
> So I would claridy here instead something like
> 
> "This deferred freeing allows for batch-freeing of page tables, 
> providing a safe context for performing a single expensive operation 
> (TLB flush) for a batch of kernel page tables instead of performing that 
> expensive operation for each page table."

The commit message has been updated, and CONFIG_ASYNC_PGTABLE_FREE has
been replaced with CONFIG_ASYNC_KERNEL_PGTABLE_FREE. Thank you for the
comments.

Thanks,
baolu