linux-kernel - Re: [RFC v11 08/14] mm: page_frag: some minor refactoring before adding new API

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Message-ID: <e532356e-3153-4132-9d20-940bc3b84ef3@huawei.com>
Date: Wed, 31 Jul 2024 20:35:08 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Alexander H Duyck <alexander.duyck@...il.com>
CC: <davem@...emloft.net>, <kuba@...nel.org>, <pabeni@...hat.com>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Andrew Morton
	<akpm@...ux-foundation.org>, <linux-mm@...ck.org>
Subject: Re: [RFC v11 08/14] mm: page_frag: some minor refactoring before
 adding new API

On 2024/7/30 23:12, Alexander H Duyck wrote:

...

>>         }
>>
>>         nc->pagecnt_bias--;
>>         nc->remaining = remaining - fragsz;
>>
>>         return encoded_page_address(encoded_va) +
>>                 (page_frag_cache_page_size(encoded_va) - remaining);
> 
> Parenthesis here shouldn't be needed, addition and subtractions
> operations can happen in any order with the result coming out the same.

I am playing safe to avoid overflow here, as I am not sure if the allocator
will give us the last page. For example, '0xfffffffffffff000 + 0x1000' will
have a overflow.