Messages in this thread | | | Subject | Re: [PATCH 21/62] net: remove the second argument of k[un]map_atomic() | From | Eric Dumazet <> | Date | Mon, 28 Nov 2011 19:26:40 +0100 |
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Le lundi 28 novembre 2011 à 10:06 -0800, Alexander Duyck a écrit : > On 11/27/2011 12:07 AM, Eric Dumazet wrote: > > But why are these drivers using kmap_atomic() in first place, since > > their fragments are allocated in regular zone (GFP_ATOMIC or > > GFP_KERNEL) ? > > I was asking the same thing myself recently when I started working on > some copy-break like code for the ixgbe driver. I believe the main > reason is a lack of documentation. This code is based loosely on the > skb_copy_bits code which will use kmap_skb_frag over all of the paged > portions of the sk_buff. As such it was decided to map things via > kmap_atomic in order to guarantee the pages had a valid virtual address. > > If I understand things correctly, what you are brining up is that pages > allocated with either GFP_ATOMIC or GFP_KERNEL will always be allocated > from the lowmem pool and as such page_address should always succeed. Is > that correct? >
Yes.
Either you could :
A) allocate high memory pages to lower pressure on LOWMEM area on 32bit kernels.
B) avoid using kmap_atomic() & kunmap_atomic() and be faster on 32bit kernels.
skb_put(skb, length); memcpy(skb->data, page_address(buffer_info->page), length);
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