On 10/16/2014 09:57 AM, Eric Dumazet wrote:
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
So if a page is used twice we are double counting the page size for the
socket then, is that correct? I just want to make sure because prior to
this patch both flows did the same thing and counted the portion of the
page used in this pass, now with this change for PAGE_SIZE of 4K we
count the entire page, and for all other cases we count the portion of
the page used.
Thanks,
Alex
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