Re: [net-next v1 02/16] net: page_pool: create hooks for custom page providers

[Mina Almasry]

On Tue, Dec 12, 2023 at 12:07 AM Ilias Apalodimas
<ilias.apalodimas@xxxxxxxxxx> wrote:
>
> Hi Mina,
>
> Apologies for not participating in the party earlier.
>

No worries, thanks for looking.

> On Fri, 8 Dec 2023 at 02:52, Mina Almasry <almasrymina@xxxxxxxxxx> wrote:
> >
> > From: Jakub Kicinski <kuba@xxxxxxxxxx>
> >
> > The page providers which try to reuse the same pages will
> > need to hold onto the ref, even if page gets released from
> > the pool - as in releasing the page from the pp just transfers
> > the "ownership" reference from pp to the provider, and provider
> > will wait for other references to be gone before feeding this
> > page back into the pool.
> >
> > Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
> > Signed-off-by: Mina Almasry <almasrymina@xxxxxxxxxx>
> >
> > ---
> >
> > This is implemented by Jakub in his RFC:
> > https://lore.kernel.org/netdev/f8270765-a27b-6ccf-33ea-cda097168d79@xxxxxxxxxx/T/
> >
> > I take no credit for the idea or implementation; I only added minor
> > edits to make this workable with device memory TCP, and removed some
> > hacky test code. This is a critical dependency of device memory TCP
> > and thus I'm pulling it into this series to make it revewable and
> > mergable.
> >
> > RFC v3 -> v1
> > - Removed unusued mem_provider. (Yunsheng).
> > - Replaced memory_provider & mp_priv with netdev_rx_queue (Jakub).
> >
> > ---
> >  include/net/page_pool/types.h | 12 ++++++++++
> >  net/core/page_pool.c          | 43 +++++++++++++++++++++++++++++++----
> >  2 files changed, 50 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h
> > index ac286ea8ce2d..0e9fa79a5ef1 100644
> > --- a/include/net/page_pool/types.h
> > +++ b/include/net/page_pool/types.h
> > @@ -51,6 +51,7 @@ struct pp_alloc_cache {
> >   * @dev:       device, for DMA pre-mapping purposes
> >   * @netdev:    netdev this pool will serve (leave as NULL if none or multiple)
> >   * @napi:      NAPI which is the sole consumer of pages, otherwise NULL
> > + * @queue:     struct netdev_rx_queue this page_pool is being created for.
> >   * @dma_dir:   DMA mapping direction
> >   * @max_len:   max DMA sync memory size for PP_FLAG_DMA_SYNC_DEV
> >   * @offset:    DMA sync address offset for PP_FLAG_DMA_SYNC_DEV
> > @@ -63,6 +64,7 @@ struct page_pool_params {
> >                 int             nid;
> >                 struct device   *dev;
> >                 struct napi_struct *napi;
> > +               struct netdev_rx_queue *queue;
> >                 enum dma_data_direction dma_dir;
> >                 unsigned int    max_len;
> >                 unsigned int    offset;
> > @@ -125,6 +127,13 @@ struct page_pool_stats {
> >  };
> >  #endif
> >
> > +struct memory_provider_ops {
> > +       int (*init)(struct page_pool *pool);
> > +       void (*destroy)(struct page_pool *pool);
> > +       struct page *(*alloc_pages)(struct page_pool *pool, gfp_t gfp);
> > +       bool (*release_page)(struct page_pool *pool, struct page *page);
> > +};
> > +
> >  struct page_pool {
> >         struct page_pool_params_fast p;
> >
> > @@ -174,6 +183,9 @@ struct page_pool {
> >          */
> >         struct ptr_ring ring;
> >
> > +       void *mp_priv;
> > +       const struct memory_provider_ops *mp_ops;
> > +
> >  #ifdef CONFIG_PAGE_POOL_STATS
> >         /* recycle stats are per-cpu to avoid locking */
> >         struct page_pool_recycle_stats __percpu *recycle_stats;
> > diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> > index ca1b3b65c9b5..f5c84d2a4510 100644
> > --- a/net/core/page_pool.c
> > +++ b/net/core/page_pool.c
> > @@ -25,6 +25,8 @@
> >
> >  #include "page_pool_priv.h"
> >
> > +static DEFINE_STATIC_KEY_FALSE(page_pool_mem_providers);
>
> We could add the existing page pool mechanisms as another 'provider',
> but I assume this is coded like this for performance reasons (IOW skip
> the expensive ptr call for the default case?)
>

Correct, it's done like this for performance reasons.

> > +
> >  #define DEFER_TIME (msecs_to_jiffies(1000))
> >  #define DEFER_WARN_INTERVAL (60 * HZ)
> >
> > @@ -174,6 +176,7 @@ static int page_pool_init(struct page_pool *pool,
> >                           const struct page_pool_params *params)
> >  {
> >         unsigned int ring_qsize = 1024; /* Default */
> > +       int err;
> >
> >         memcpy(&pool->p, &params->fast, sizeof(pool->p));
> >         memcpy(&pool->slow, &params->slow, sizeof(pool->slow));
> > @@ -234,10 +237,25 @@ static int page_pool_init(struct page_pool *pool,
> >         /* Driver calling page_pool_create() also call page_pool_destroy() */
> >         refcount_set(&pool->user_cnt, 1);
> >
> > +       if (pool->mp_ops) {
> > +               err = pool->mp_ops->init(pool);
> > +               if (err) {
> > +                       pr_warn("%s() mem-provider init failed %d\n",
> > +                               __func__, err);
> > +                       goto free_ptr_ring;
> > +               }
> > +
> > +               static_branch_inc(&page_pool_mem_providers);
> > +       }
> > +
> >         if (pool->p.flags & PP_FLAG_DMA_MAP)
> >                 get_device(pool->p.dev);
> >
> >         return 0;
> > +
> > +free_ptr_ring:
> > +       ptr_ring_cleanup(&pool->ring, NULL);
> > +       return err;
> >  }
> >
> >  static void page_pool_uninit(struct page_pool *pool)
> > @@ -519,7 +537,10 @@ struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp)
> >                 return page;
> >
> >         /* Slow-path: cache empty, do real allocation */
> > -       page = __page_pool_alloc_pages_slow(pool, gfp);
> > +       if (static_branch_unlikely(&page_pool_mem_providers) && pool->mp_ops)
>
> Why do we need && pool->mp_ops? On the init function, we only bump
> page_pool_mem_providers if the ops are there
>

Note that page_pool_mem_providers is a static variable (not part of
the page_pool struct), so if you have 2 page_pools on the system, one
using devmem and one not, we need to check pool->mp_ops to make sure
this page_pool is using a memory provider.

> > +               page = pool->mp_ops->alloc_pages(pool, gfp);
> > +       else
> > +               page = __page_pool_alloc_pages_slow(pool, gfp);
> >         return page;
> >  }
> >  EXPORT_SYMBOL(page_pool_alloc_pages);
> > @@ -576,10 +597,13 @@ void __page_pool_release_page_dma(struct page_pool *pool, struct page *page)
> >  void page_pool_return_page(struct page_pool *pool, struct page *page)
> >  {
> >         int count;
> > +       bool put;
> >
> > -       __page_pool_release_page_dma(pool, page);
> > -
> > -       page_pool_clear_pp_info(page);
> > +       put = true;
> > +       if (static_branch_unlikely(&page_pool_mem_providers) && pool->mp_ops)
>
> ditto
>
> > +               put = pool->mp_ops->release_page(pool, page);
> > +       else
> > +               __page_pool_release_page_dma(pool, page);
> >
> >         /* This may be the last page returned, releasing the pool, so
> >          * it is not safe to reference pool afterwards.
> > @@ -587,7 +611,10 @@ void page_pool_return_page(struct page_pool *pool, struct page *page)
> >         count = atomic_inc_return_relaxed(&pool->pages_state_release_cnt);
> >         trace_page_pool_state_release(pool, page, count);
> >
> > -       put_page(page);
> > +       if (put) {
> > +               page_pool_clear_pp_info(page);
> > +               put_page(page);
> > +       }
> >         /* An optimization would be to call __free_pages(page, pool->p.order)
> >          * knowing page is not part of page-cache (thus avoiding a
> >          * __page_cache_release() call).
> > @@ -857,6 +884,12 @@ static void __page_pool_destroy(struct page_pool *pool)
> >
> >         page_pool_unlist(pool);
> >         page_pool_uninit(pool);
> > +
> > +       if (pool->mp_ops) {
>
> Same here. Using a mix of pool->mp_ops and page_pool_mem_providers
> will work, but since we always check the ptr on init, can't we simply
> rely on page_pool_mem_providers for the rest of the code?
>
> Thanks
> /Ilias
> > +               pool->mp_ops->destroy(pool);
> > +               static_branch_dec(&page_pool_mem_providers);
> > +       }
> > +
> >         kfree(pool);
> >  }
> >
> > --
> > 2.43.0.472.g3155946c3a-goog
> >



--
Thanks,
Mina