Re: tcp_sendpage and page allocation lifetime vs. iscsi

[Avi Kivity]

David S. Miller wrote:

> On Mon, 25 Apr 2005 22:11:16 +0300
> Avi Kivity <avi@xxxxxxxxxx> wrote:
>
>  
>
> > you need a completion to tell you when your buffer has been sent. you 
> > can use the kiocb parameter to tcp_sendmsg, as it has a completion. 
> > however, tcp_sendmsg does not appear to use it.
> >
> > in effect, you need tcp aio, but the mainline kernel does not support it 
> > yet.
> >    
>
> Or, he could simply not try to reuse the private buffer he is
> giving to TCP.
>  
you are describing a memory leak. at some point he must free (or 
otherwise reuse) these pages.

theoretically he could peek at the tcp sequence number, but an 
event-driven, protocol-agnostic completion seems better to me.

* light goes on *

yes, if he frees the pages immediately after tcp_sendpage, then the 
reference count would remain elevated until tcp completes sending these 
pages. so the sequence

 allocate pages
 fill with data
 tcp_sendpage()
 free pages

should be safe?

(I am still wishing for tcp aio, though)

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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