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From: David Hildenbrand <david@redhat.com>
To: Qi Zheng <zhengqi.arch@bytedance.com>, Jason Gunthorpe <jgg@ziepe.ca>
Cc: akpm@linux-foundation.org, tglx@linutronix.de,
	hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com,
	kirill.shutemov@linux.intel.com, mika.penttila@nextfour.com,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, songmuchun@bytedance.com
Subject: Re: [PATCH v2 0/9] Free user PTE page table pages
Date: Thu, 16 Sep 2021 10:30:21 +0200	[thread overview]
Message-ID: <b7514329-7ae4-b78e-a4f1-4208c9cfe802@redhat.com> (raw)
In-Reply-To: <d33a4349-a228-f98a-ab14-e221bf80dd4a@bytedance.com>

On 16.09.21 07:32, Qi Zheng wrote:
> 
> 
> On 9/15/21 10:59 PM, Jason Gunthorpe wrote:
>> On Wed, Sep 15, 2021 at 10:52:40PM +0800, Qi Zheng wrote:
>>> I am going to split this patch series as follows:
>>>
>>> 1. Introduce the new dummy APIs, which is an empty implementation.
>>>      But I will explain its semantics.
>>> 2. Merge #6, #7 and #8, and call these dummy APIs in any necessary
>>>      location, and split some special cases into single patches, such as
>>>      pagefault and gup, etc. So that we can explain in more detail the
>>>      concurrency in these cases. For example, we don't need to hold any
>>>      pte_refcount in the fast path in gup on the x86_64 platform. Because
>>>      the PTE page can't be freed after the local CPU interrupt is closed
>>>      in the fast path in gup.
>>> 3. Introduce CONFIG_FREE_USER_PTE and implement these empty dummy APIs.
>>> 4. Add a description document.
>>>
>>> And I try to add a function that combines pte_offset_map() and
>>> pte_try_get(). Maybe the func name is pte_try_map() recommended by
>>> Jason, or keep the pte_offset_map() unchanged?
>>
>> It is part of the transformation, add a
>> pte_try_map()/pte_undo_try_map() and replace all the pte_offset_map()
>> callsites that can use the new API with it. The idea was that try_map
>> would incorporate the pmd_trans_unstable/etc mess so searching for
>> trans_unstable is a good place to start finding candidates. Some are
>> simple, some are tricky.
> 
> Yes, I will search pte_offset_map()/pmd_trans_unstable/etc, and then
> analyze the specific situation.

Maybe propose the new API first, before doing the actual implementation. 
Might safe you from doing some additional back-and-forth
work eventually.


-- 
Thanks,

David / dhildenb


  reply	other threads:[~2021-09-16  8:30 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-19  3:18 [PATCH v2 0/9] Free user PTE page table pages Qi Zheng
2021-08-19  3:18 ` [PATCH v2 1/9] mm: introduce pmd_install() helper Qi Zheng
2021-08-24 16:26   ` David Hildenbrand
2021-08-25 16:20     ` Qi Zheng
2021-08-25 16:32       ` David Hildenbrand
2021-08-26  3:04         ` Qi Zheng
2021-08-19  3:18 ` [PATCH v2 2/9] mm: remove redundant smp_wmb() Qi Zheng
2021-08-19  3:18 ` [PATCH v2 3/9] mm: rework the parameter of lock_page_or_retry() Qi Zheng
2021-08-19  3:18 ` [PATCH v2 4/9] mm: move pte_alloc{,_map,_map_lock}() to a separate file Qi Zheng
2021-08-19  3:18 ` [PATCH v2 5/9] mm: pte_refcount infrastructure Qi Zheng
2021-08-19  3:18 ` [PATCH v2 6/9] mm: free user PTE page table pages Qi Zheng
2021-08-19  7:01   ` David Hildenbrand
2021-08-19 10:18     ` [External] " Qi Zheng
2021-09-01 13:53   ` Jason Gunthorpe
2021-09-01 13:57     ` David Hildenbrand
2021-09-01 15:32       ` Jason Gunthorpe
2021-09-01 16:13         ` David Hildenbrand
2021-09-01 16:16           ` Jason Gunthorpe
2021-09-01 16:19             ` David Hildenbrand
2021-09-01 17:10               ` Jason Gunthorpe
2021-09-01 17:49                 ` David Hildenbrand
2021-09-01 17:55                   ` Jason Gunthorpe
2021-09-01 17:58                     ` David Hildenbrand
2021-09-01 18:09                       ` Jason Gunthorpe
2021-09-01 18:10                         ` David Hildenbrand
2021-09-02  7:04                     ` Qi Zheng
2021-09-02  6:53         ` Qi Zheng
2021-08-19  3:18 ` [PATCH v2 7/9] mm: add THP support for pte_ref Qi Zheng
2021-08-19  3:18 ` [PATCH v2 8/9] mm: free PTE page table by using rcu mechanism Qi Zheng
2021-08-19  3:18 ` [PATCH v2 9/9] mm: use mmu_gather to free PTE page table Qi Zheng
2021-09-01 12:32 ` [PATCH v2 0/9] Free user PTE page table pages David Hildenbrand
2021-09-01 16:07   ` Jason Gunthorpe
2021-09-01 16:10     ` David Hildenbrand
2021-09-02  3:37   ` Qi Zheng
2021-09-15 14:52   ` Qi Zheng
2021-09-15 14:59     ` Jason Gunthorpe
2021-09-16  5:32       ` Qi Zheng
2021-09-16  8:30         ` David Hildenbrand [this message]
2021-09-16  8:41           ` Qi Zheng

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