Re: [PATCH V3,net-next, 2/4] net: mana: Refactor RX buffer allocation code to prepare for various MTU

[Leon Romanovsky]

On Thu, Apr 13, 2023 at 02:03:50PM +0000, Haiyang Zhang wrote:
> 
> 
> > -----Original Message-----
> > From: Leon Romanovsky <leon@xxxxxxxxxx>
> > Sent: Thursday, April 13, 2023 9:04 AM
> > To: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> > Cc: linux-hyperv@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; Dexuan Cui
> > <decui@xxxxxxxxxxxxx>; KY Srinivasan <kys@xxxxxxxxxxxxx>; Paul Rosswurm
> > <paulros@xxxxxxxxxxxxx>; olaf@xxxxxxxxx; vkuznets@xxxxxxxxxx;
> > davem@xxxxxxxxxxxxx; wei.liu@xxxxxxxxxx; edumazet@xxxxxxxxxx;
> > kuba@xxxxxxxxxx; pabeni@xxxxxxxxxx; Long Li <longli@xxxxxxxxxxxxx>;
> > ssengar@xxxxxxxxxxxxxxxxxxx; linux-rdma@xxxxxxxxxxxxxxx;
> > daniel@xxxxxxxxxxxxx; john.fastabend@xxxxxxxxx; bpf@xxxxxxxxxxxxxxx;
> > ast@xxxxxxxxxx; Ajay Sharma <sharmaajay@xxxxxxxxxxxxx>;
> > hawk@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > Subject: Re: [PATCH V3,net-next, 2/4] net: mana: Refactor RX buffer allocation
> > code to prepare for various MTU
> > 
> > On Wed, Apr 12, 2023 at 02:16:01PM -0700, Haiyang Zhang wrote:
> > > Move out common buffer allocation code from mana_process_rx_cqe() and
> > > mana_alloc_rx_wqe() to helper functions.
> > > Refactor related variables so they can be changed in one place, and buffer
> > > sizes are in sync.
> > >
> > > Signed-off-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> > > Reviewed-by: Jesse Brandeburg <jesse.brandeburg@xxxxxxxxx>
> > > ---
> > > V3:
> > > Refectored to multiple patches for readability. Suggested by Jacob Keller.
> > >
> > > V2:
> > > Refectored to multiple patches for readability. Suggested by Yunsheng Lin.
> > >
> > > ---
> > >  drivers/net/ethernet/microsoft/mana/mana_en.c | 154 ++++++++++-------
> > -
> > >  include/net/mana/mana.h                       |   6 +-
> > >  2 files changed, 91 insertions(+), 69 deletions(-)
> > 
> > <...>
> > 
> > > +static void *mana_get_rxfrag(struct mana_rxq *rxq, struct device *dev,
> > > +			     dma_addr_t *da, bool is_napi)
> > > +{
> > > +	struct page *page;
> > > +	void *va;
> > > +
> > > +	/* Reuse XDP dropped page if available */
> > > +	if (rxq->xdp_save_va) {
> > > +		va = rxq->xdp_save_va;
> > > +		rxq->xdp_save_va = NULL;
> > > +	} else {
> > > +		page = dev_alloc_page();
> > 
> > Documentation/networking/page_pool.rst
> >    10 Basic use involves replacing alloc_pages() calls with the
> >    11 page_pool_alloc_pages() call.  Drivers should use
> > page_pool_dev_alloc_pages()
> >    12 replacing dev_alloc_pages().
> > 
> > General question, is this sentence applicable to all new code or only
> > for XDP related paths?
> 
> Quote from the context before that sentence --
> 
> =============
> Page Pool API
> =============
> The page_pool allocator is optimized for the XDP mode that uses one frame
> per-page, but it can fallback on the regular page allocator APIs.
> Basic use involves replacing alloc_pages() calls with the
> page_pool_alloc_pages() call.  Drivers should use page_pool_dev_alloc_pages()
> replacing dev_alloc_pages().
> 
> --unquote
> 
> So the page pool is optimized for the XDP, and that sentence is applicable to drivers
> that have set up page pool for XDP optimization.

"but it can fallback on the regular page allocator APIs."

> static inline struct page *page_pool_dev_alloc_pages(struct page_pool *pool)  //need a pool been set up
> 
> Back to our mana driver, we don't have page pool setup yet. (will consider in the future)
> So we cannot call page_pool_dev_alloc_pages(pool) in this place yet.

ok, thanks

> 
> Thanks,
> - Haiyang
>