netdev - Re: [PATCH v2] mm, page_pool: introduce a new page type for page pool in page type

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Message-ID: <7d7eb3cd-db7e-4a9e-8671-4185b716bbc8@gmail.com>
Date: Tue, 29 Jul 2025 09:53:31 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Byungchul Park <byungchul@...com>
Cc: Mina Almasry <almasrymina@...gle.com>, linux-mm@...ck.org,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH v2] mm, page_pool: introduce a new page type for page pool
 in page type

On 7/29/25 02:04, Byungchul Park wrote:
> On Mon, Jul 28, 2025 at 07:49:30PM +0100, Pavel Begunkov wrote:
>> On 7/28/25 19:39, Mina Almasry wrote:
>>> On Mon, Jul 28, 2025 at 11:35 AM Pavel Begunkov <asml.silence@...il.com> wrote:

...>>> This may be my bad since I said we should check if it's 0 initialized.
>>>
>>> It looks like on the devmem side as well we kvmalloc_array the niovs,
>>> and if I'm checking through the helpers right, kvmalloc_array does
>>> 0-initialize indeed.
>>
>> I wouldn't rely on that, it's just for zcrx I do:
>>
>> kvmalloc_array(...,  GFP_KERNEL | __GFP_ZERO);
> 
> For net_devmem_bind_dmabuf(), __GFP_ZERO will add bigger overhead than
> just assignment, 'niov->pp = NULL'.

That's not a place where you should care about zeroing overhead.

> I'd like to ask you if you are still good with __GFP_ZERO overhead
> before going ahead.

However, it might be easier for you to just assign it directly
for devmem and let Mina add GFP_ZERO if he fancy the idea.

-- 
Pavel Begunkov