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

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Message-ID: <20230413163059.GS17993@unreal>
Date:   Thu, 13 Apr 2023 19:30:59 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Haiyang Zhang <haiyangz@...rosoft.com>
Cc:     "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Paul Rosswurm <paulros@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        Long Li <longli@...rosoft.com>,
        "ssengar@...ux.microsoft.com" <ssengar@...ux.microsoft.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "john.fastabend@...il.com" <john.fastabend@...il.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        Ajay Sharma <sharmaajay@...rosoft.com>,
        "hawk@...nel.org" <hawk@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3,net-next, 2/4] net: mana: Refactor RX buffer
 allocation code to prepare for various MTU

On Thu, Apr 13, 2023 at 02:03:50PM +0000, Haiyang Zhang wrote:
> 
> 
> > -----Original Message-----
> > From: Leon Romanovsky <leon@...nel.org>
> > Sent: Thursday, April 13, 2023 9:04 AM
> > To: Haiyang Zhang <haiyangz@...rosoft.com>
> > Cc: linux-hyperv@...r.kernel.org; netdev@...r.kernel.org; Dexuan Cui
> > <decui@...rosoft.com>; KY Srinivasan <kys@...rosoft.com>; Paul Rosswurm
> > <paulros@...rosoft.com>; olaf@...fle.de; vkuznets@...hat.com;
> > davem@...emloft.net; wei.liu@...nel.org; edumazet@...gle.com;
> > kuba@...nel.org; pabeni@...hat.com; Long Li <longli@...rosoft.com>;
> > ssengar@...ux.microsoft.com; linux-rdma@...r.kernel.org;
> > daniel@...earbox.net; john.fastabend@...il.com; bpf@...r.kernel.org;
> > ast@...nel.org; Ajay Sharma <sharmaajay@...rosoft.com>;
> > hawk@...nel.org; linux-kernel@...r.kernel.org
> > 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@...rosoft.com>
> > > Reviewed-by: Jesse Brandeburg <jesse.brandeburg@...el.com>
> > > ---
> > > 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
>