linux-kernel - Re: [PATCH net-next v4 1/9] net: add get_netmem/put

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Message-ID: <Z7eDqnkwmpTW5963@mini-arch>
Date: Thu, 20 Feb 2025 11:34:02 -0800
From: Stanislav Fomichev <stfomichev@...il.com>
To: Mina Almasry <almasrymina@...gle.com>
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Subject: Re: [PATCH net-next v4 1/9] net: add get_netmem/put_netmem support

On 02/20, Mina Almasry wrote:
> Currently net_iovs support only pp ref counts, and do not support a
> page ref equivalent.
> 
> This is fine for the RX path as net_iovs are used exclusively with the
> pp and only pp refcounting is needed there. The TX path however does not
> use pp ref counts, thus, support for get_page/put_page equivalent is
> needed for netmem.
> 
> Support get_netmem/put_netmem. Check the type of the netmem before
> passing it to page or net_iov specific code to obtain a page ref
> equivalent.
> 
> For dmabuf net_iovs, we obtain a ref on the underlying binding. This
> ensures the entire binding doesn't disappear until all the net_iovs have
> been put_netmem'ed. We do not need to track the refcount of individual
> dmabuf net_iovs as we don't allocate/free them from a pool similar to
> what the buddy allocator does for pages.
> 
> This code is written to be extensible by other net_iov implementers.
> get_netmem/put_netmem will check the type of the netmem and route it to
> the correct helper:
> 
> pages -> [get|put]_page()
> dmabuf net_iovs -> net_devmem_[get|put]_net_iov()
> new net_iovs ->	new helpers
> 
> Signed-off-by: Mina Almasry <almasrymina@...gle.com>

Acked-by: Stanislav Fomichev <sdf@...ichev.me>

I remember you wanted to have more fine grained refcnt, but starting
with this is good enough for me.