Hi,
I've been trying to understand kernel_sendpage but I've not been able to figure
it out completely and hopefully someone else knows better so please help me out
on this.
I'm using kernel_sendpage for a TCP connection and it works well when there are
lesser number of kernel threads trying to send data using it.
Now the page I hand over to kernel_sendpage is reused again for reading data
from the socket and then processing it and then again resending the processed
data in the same page again. It's at maximum 2KB data and never lesser than 120
bytes.
As I see it in the code, the page isn't copied in the skb frags array it's just
assigned and get_page is called to increment the page reference count. (I don't
free it anyway until the thread is stopped and it never is unless it gets a
signal).
Now I don't know wether kernel_sendpage will wait for the page to be sent or it
won't. I've tried with MSG_DONTWAIT and passing 0 for flags but after every now
and then the problem occurs at client which I'm describing below with the best
explanation I could think of...
When too many kernel threads are trying to send data using
kernel_sendpage, with NO MSG_DONTWAIT flag, then also it seems that this call
succeeds? However since I'm reusing the page the data can get overridden by the
next sock_recvmsg and when the network stack is ready to send my page it gets
garbage data at client?
The same issue I observed with MSG_DONTWAIT set even in that case the client
sometimes get garbage data.
So my query is,
To use kernel_sendpage what I need to do in order to be sure that network stack
indeed has sent my page and that I can reuse it for sock_recvmsg again.
Thanks a lot for reading!
Regards,
Pranay Kr. Srivastava
[email protected]
Software Engineer
ERS,HCL Technologies
A-5, Sector 24, Noida 201301, U.P. (India)
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