netdev - Re: [net-next PATCH 1/6] net: Split netdev_alloc_frag into __alloc_page_frag and add __napi_alloc

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Date:	Tue, 9 Dec 2014 20:16:14 -0800
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Alexander Duyck <alexander.h.duyck@...hat.com>
Cc:	Network Development <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [net-next PATCH 1/6] net: Split netdev_alloc_frag into
 __alloc_page_frag and add __napi_alloc_frag

On Tue, Dec 9, 2014 at 7:40 PM, Alexander Duyck
<alexander.h.duyck@...hat.com> wrote:
> This patch splits the netdev_alloc_frag function up so that it can be used
> on one of two page frag pools instead of being fixed on the
> netdev_alloc_cache.  By doing this we can add a NAPI specific function
> __napi_alloc_frag that accesses a pool that is only used from softirq
> context.  The advantage to this is that we do not need to call
> local_irq_save/restore which can be a significant savings.
>
> I also took the opportunity to refactor the core bits that were placed in
> __alloc_page_frag.  First I updated the allocation to do either a 32K
> allocation or an order 0 page.  This is based on the changes in commmit
> d9b2938aa where it was found that latencies could be reduced in case of

thanks for explaining that piece of it.

> +       struct page *page = NULL;
> +       gfp_t gfp = gfp_mask;
> +
> +       if (order) {
> +               gfp_mask |= __GFP_COMP | __GFP_NOWARN | __GFP_NORETRY;
> +               page = alloc_pages_node(NUMA_NO_NODE, gfp_mask, order);
> +               nc->frag.size = PAGE_SIZE << (page ? order : 0);
> +       }
>
> -       local_irq_save(flags);
> -       nc = this_cpu_ptr(&netdev_alloc_cache);
> -       if (unlikely(!nc->frag.page)) {
> +       if (unlikely(!page))
> +               page = alloc_pages_node(NUMA_NO_NODE, gfp, 0);

I'm guessing you're not combining this 'if' with above one to
keep gfp untouched, so there is a 'warn' when it actually fails 2nd time.
Tricky :)
Anyway looks good to me and I think I understand it enough to say:
Acked-by: Alexei Starovoitov <ast@...mgrid.com>
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