netdev - Re: [net RFC] net/mlx4_en: Use frag stride in crossing page boundary condition

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Date:   Thu, 14 Jun 2018 12:12:16 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Saeed Mahameed <saeedm@...lanox.com>,
        "eric.dumazet@...il.com" <eric.dumazet@...il.com>,
        "kafai@...com" <kafai@...com>, Tariq Toukan <tariqt@...lanox.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>
Subject: Re: [net RFC] net/mlx4_en: Use frag stride in crossing page boundary
 condition



On 06/14/2018 11:56 AM, Saeed Mahameed wrote:

> Interestingly for this exact frag_stride we don't have an issue :)
> since it goes through a different condition branch
> (the page flipping thing):
> 
> if (frag_info->frag_stride == PAGE_SIZE / 2) {
>     frags->page_offset ^= PAGE_SIZE / 2;
> 	release = page_count(page) != 1 ||
> 		  page_is_pfmemalloc(page) ||
> 		  page_to_nid(page) != numa_mem_id();
> 

I guess you forgot to test on PowerPC where PAGE_SIZE=65536 ?

On PowerPC, the first branch is never taken.