On Thu, 2014-10-16 at 08:28 -0700, Alexander Duyck wrote:
> I think the part you are not getting is that is how buffers are
> essentially handled now. So for example in the case if igb the only
> part we have copied out is usually the header, or the entire frame in
> the case of small packets. This has to happen in order to allow for
> changes to the header for routing and such. Beyond that the frags that
> are passed are the buffers that igb is still holding onto. So
> effectively what the other device transmits in a bridging/routing
> scenario is my own net card specified buffer plus the copied/modified
> header.
>
> For a brief period igb used build_skb but that isn't valid on most
> systems as memory mapped for a device can be overwritten if the page is
> unmapped resulting in any changes to the header for routing/bridging
> purposes being invalidated. Thus we cannot use the buffers for both the
> skb->data header which may be changed and Rx DMA simultaneously.
This reminds me that igb still has skb->truesize underestimation by 100%
If a fragment is held in some socket receive buffer, a full page is
consumed, not 2048 bytes.
diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index a21b14495ebd..56ca6c78985e 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -6586,9 +6586,11 @@ static bool igb_add_rx_frag(struct igb_ring *rx_ring,
struct page *page = rx_buffer->page;
unsigned int size = le16_to_cpu(rx_desc->wb.upper.length);
#if (PAGE_SIZE < 8192)
- unsigned int truesize = IGB_RX_BUFSZ;
+ unsigned int segsize = IGB_RX_BUFSZ;
+ unsigned int truesize = PAGE_SIZE;
#else
- unsigned int truesize = ALIGN(size, L1_CACHE_BYTES);
+ unsigned int segsize = ALIGN(size, L1_CACHE_BYTES);
+ unsigned int truesize = segsize;
#endif
if ((size <= IGB_RX_HDR_LEN) && !skb_is_nonlinear(skb)) {
@@ -6614,7 +6616,7 @@ static bool igb_add_rx_frag(struct igb_ring *rx_ring,
skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, page,
rx_buffer->page_offset, size, truesize);
- return igb_can_reuse_rx_page(rx_buffer, page, truesize);
+ return igb_can_reuse_rx_page(rx_buffer, page, segsize);
}
static struct sk_buff *igb_fetch_rx_buffer(struct igb_ring *rx_ring,
--
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