netdev - Re: [PATCH v4 04/17] octeontx2-pf: Initialize and config queues

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Message-ID: <20200123062017.3cbefe70@cakuba>
Date:   Thu, 23 Jan 2020 06:20:17 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Sunil Kovvuri <sunil.kovvuri@...il.com>
Cc:     Linux Netdev List <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Michal Kubecek <mkubecek@...e.cz>,
        Sunil Goutham <sgoutham@...vell.com>,
        Geetha sowjanya <gakula@...vell.com>
Subject: Re: [PATCH v4 04/17] octeontx2-pf: Initialize and config queues

On Thu, 23 Jan 2020 00:59:54 +0530, Sunil Kovvuri wrote:
> On Tue, Jan 21, 2020 at 9:31 PM Jakub Kicinski <kuba@...nel.org> wrote:
> > On Tue, 21 Jan 2020 18:51:38 +0530, sunil.kovvuri@...il.com wrote:  
> > > +dma_addr_t otx2_alloc_rbuf(struct otx2_nic *pfvf, struct otx2_pool *pool,
> > > +                        gfp_t gfp)
> > > +{
> > > +     dma_addr_t iova;
> > > +
> > > +     /* Check if request can be accommodated in previous allocated page */
> > > +     if (pool->page &&
> > > +         ((pool->page_offset + pool->rbsize) <= PAGE_SIZE)) {

You use straight PAGE_SIZE here

> > > +             pool->pageref++;
> > > +             goto ret;
> > > +     }
> > > +
> > > +     otx2_get_page(pool);
> > > +
> > > +     /* Allocate a new page */
> > > +     pool->page = alloc_pages(gfp | __GFP_COMP | __GFP_NOWARN,
> > > +                              pool->rbpage_order);

but allocate with order

> > > +     if (unlikely(!pool->page))
> > > +             return -ENOMEM;
> > > +
> > > +     pool->page_offset = 0;
> > > +ret:
> > > +     iova = (u64)otx2_dma_map_page(pfvf, pool->page, pool->page_offset,
> > > +                                   pool->rbsize, DMA_FROM_DEVICE);
> > > +     if (!iova) {
> > > +             if (!pool->page_offset)
> > > +                     __free_pages(pool->page, pool->rbpage_order);
> > > +             pool->page = NULL;
> > > +             return -ENOMEM;
> > > +     }
> > > +     pool->page_offset += pool->rbsize;
> > > +     return iova;
> > > +}  
> >
> > You don't seem to be doing any page recycling if I'm reading this right.
> > Can't you use the standard in-kernel page frag allocator
> > (netdev_alloc_frag/napi_alloc_frag)?  
> 
> netdev_alloc_frag() is costly.
> eg: it does updates to page's refcount per frag allocation.

It would be nice to see it improve rather than have drivers implement 
a slight variation of the scheme :/