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Re: [Xen-devel] [3.15-rc3] Bisected: xen-netback mangles packets between two guests on a bridge since merge of "TX grant mapping with SKBTX_DEV_ZEROCOPY instead of copy" series.

On 02/05/14 15:06, Sander Eikelenboom wrote:

Friday, May 2, 2014, 4:00:40 PM, you wrote:

Let's see what that does different and if that gives an insight in what is going

The debug patch that i used is attached.
Here is some of the output, skb->data_len size sometimes varies slightly as does 
skb->truesize (is that allowed to become > 64k ?).
Yes, truesize can be over 64K, as it includes the aligned size of the
data itself (64k max), struct skbuff and struct shared_info.
However my calculation for the truesize might be wrong: I count all the
frags as full sized pages (skb->truesize += i * PAGE_SIZE), but the last
page is not necessarily used entirely by that frag.
I had the idea that truesize should include the size of the whole page
as we reserved it with alloc_page for this skb, but it might not be true.
Btw. with you "skb->>truesize -= nskb->data_len;" version truesize should
end up around 128k, something entirely wrong. Can you try with
"skb->>truesize -= nskb->data_len;" in that line?
My repro env is underway in the meantime ...

Erhmm i don't get this last part, first you entitle
"skb->truesize -= nskb->data_len;" as being "entirely wrong" (which is probably 

Then you want me to try just that ? .. or did you mean something else ?

Sorry, I was misleading and wrong. Can you try out this scenario with the attached patch?



Attachment: truesize.patch
Description: Text Data

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