linux-kernel - Re: [PATCH v3 15/17] mm: pgtable: remove tlb_remove_page

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Message-ID: <a84a7b0f-dad5-4100-9d0c-3b515e7fb71f@bytedance.com>
Date: Mon, 6 Jan 2025 11:53:36 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: Peter Zijlstra <peterz@...radead.org>, Mike Rapoport <rppt@...nel.org>
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Subject: Re: [PATCH v3 15/17] mm: pgtable: remove tlb_remove_page_ptdesc()



On 2025/1/3 19:14, Peter Zijlstra wrote:
> On Sat, Dec 28, 2024 at 11:26:22AM +0200, Mike Rapoport wrote:
>> On Mon, Dec 23, 2024 at 05:41:01PM +0800, Qi Zheng wrote:
>>> Here we are explicitly dealing with struct page, and the following logic
>>> semms strange:
>>>
>>> tlb_remove_page_ptdesc((tlb), (page_ptdesc(pte)));
>>>
>>> tlb_remove_page_ptdesc
>>> --> tlb_remove_page(tlb, ptdesc_page(pt));
>>>
>>> So remove tlb_remove_page_ptdesc() and make callers call tlb_remove_page()
>>> directly.
>>
>> Please don't. The ptdesc wrappers are there as a part of reducing the size
>> of struct page project [1].
>>
>> For now struct ptdesc overlaps struct page, but the goal is to have them
>> separate and always operate on struct ptdesc when working with page tables.
> 
> I don't see how the current idiotic code helps with that at all.
> 
> Fundamentally tlb_remove_page() is about removing *pages* as from a PTE,
> there should not be a page-table anywhere near here *ever*.
> 
> Yes, some architectures use tlb_remove_page() for page-tables too, but
> that is more or less an implementation detail that can be fixed.
> 
> So no, please keep these patches and kill this utterly idiotic code.
> 
> The only thing that should eventually care about page-tables is
> tlb_remove_table(), and that takes a 'void *' and is expected to match
> whatever __tlb_remove_table() does.
> 
> Flipping those to pgdesc, once its actually a thing, should be fairly
> straight forward.

Well, since I've already sent v4, and that patch series is mainly for
bug fix, I'll send a separate patch series to do this.

Thanks!