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Message-ID: <7b6eb498082145d8a4bd5ecd741081355f52d523.camel@mellanox.com>
Date: Wed, 23 Oct 2019 19:09:59 +0000
From: Saeed Mahameed <saeedm@...lanox.com>
To: "ilias.apalodimas@...aro.org" <ilias.apalodimas@...aro.org>,
"brouer@...hat.com" <brouer@...hat.com>
CC: "jonathan.lemon@...il.com" <jonathan.lemon@...il.com>,
"davem@...emloft.net" <davem@...emloft.net>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 3/4] page_pool: Restructure
__page_pool_put_page()
On Wed, 2019-10-23 at 20:31 +0200, Jesper Dangaard Brouer wrote:
> On Wed, 23 Oct 2019 11:45:15 +0300
> Ilias Apalodimas <ilias.apalodimas@...aro.org> wrote:
>
> > On Tue, Oct 22, 2019 at 04:44:24AM +0000, Saeed Mahameed wrote:
> > > From: Jonathan Lemon <jonathan.lemon@...il.com>
> > >
> > > 1) Rename functions to reflect what they are actually doing.
> > >
> > > 2) Unify the condition to keep a page.
> > >
> > > 3) When page can't be kept in cache, fallback to releasing page
> > > to page
> > > allocator in one place, instead of calling it from multiple
> > > conditions,
> > > and reuse __page_pool_return_page().
> > >
> > > Signed-off-by: Jonathan Lemon <jonathan.lemon@...il.com>
> > > Signed-off-by: Saeed Mahameed <saeedm@...lanox.com>
> > > ---
> > > net/core/page_pool.c | 38 +++++++++++++++++++-------------------
> > > 1 file changed, 19 insertions(+), 19 deletions(-)
> > >
> > > diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> > > index 8120aec999ce..65680aaa0818 100644
> > > --- a/net/core/page_pool.c
> > > +++ b/net/core/page_pool.c
> > > @@ -258,6 +258,7 @@ static bool
> > > __page_pool_recycle_into_ring(struct page_pool *pool,
> > > struct page *page)
> > > {
> > > int ret;
> > > +
> > > /* BH protection not needed if current is serving softirq */
> > > if (in_serving_softirq())
> > > ret = ptr_ring_produce(&pool->ring, page);
> > > @@ -272,8 +273,8 @@ static bool
> > > __page_pool_recycle_into_ring(struct page_pool *pool,
> > > *
> > > * Caller must provide appropriate safe context.
> > > */
> > > -static bool __page_pool_recycle_direct(struct page *page,
> > > - struct page_pool *pool)
> > > +static bool __page_pool_recycle_into_cache(struct page *page,
> > > + struct page_pool *pool)
> > > {
> > > if (unlikely(pool->alloc.count == PP_ALLOC_CACHE_SIZE))
> > > return false;
> > > @@ -283,15 +284,18 @@ static bool
> > > __page_pool_recycle_direct(struct page *page,
> > > return true;
> > > }
> > >
> > > -/* page is NOT reusable when:
> > > - * 1) allocated when system is under some pressure.
> > > (page_is_pfmemalloc)
> > > - * 2) belongs to a different NUMA node than pool->p.nid.
> > > +/* Keep page in caches only if page:
> > > + * 1) wasn't allocated when system is under some pressure
> > > (page_is_pfmemalloc).
> > > + * 2) belongs to pool's numa node (pool->p.nid).
> > > + * 3) refcount is 1 (owned by page pool).
> > > *
> > > * To update pool->p.nid users must call page_pool_update_nid.
> > > */
> > > -static bool pool_page_reusable(struct page_pool *pool, struct
> > > page *page)
> > > +static bool page_pool_keep_page(struct page_pool *pool, struct
> > > page *page)
> > > {
> > > - return !page_is_pfmemalloc(page) && page_to_nid(page) == pool-
> > > >p.nid;
> > > + return !page_is_pfmemalloc(page) &&
> > > + page_to_nid(page) == pool->p.nid &&
> > > + page_ref_count(page) == 1;
> > > }
> > >
> > > void __page_pool_put_page(struct page_pool *pool,
> > > @@ -300,22 +304,19 @@ void __page_pool_put_page(struct page_pool
> > > *pool,
> > > /* This allocator is optimized for the XDP mode that uses
> > > * one-frame-per-page, but have fallbacks that act like the
> > > * regular page allocator APIs.
> > > - *
> > > - * refcnt == 1 means page_pool owns page, and can recycle it.
> > > */
> > > - if (likely(page_ref_count(page) == 1 &&
> > > - pool_page_reusable(pool, page))) {
> > > +
> > > + if (likely(page_pool_keep_page(pool, page))) {
> > > /* Read barrier done in page_ref_count / READ_ONCE */
> > >
> > > if (allow_direct && in_serving_softirq())
> > > - if (__page_pool_recycle_direct(page, pool))
> > > + if (__page_pool_recycle_into_cache(page, pool))
> > > return;
> > >
> > > - if (!__page_pool_recycle_into_ring(pool, page)) {
> > > - /* Cache full, fallback to free pages */
> > > - __page_pool_return_page(pool, page);
> > > - }
> > > - return;
> > > + if (__page_pool_recycle_into_ring(pool, page))
> > > + return;
> > > +
> > > + /* Cache full, fallback to return pages */
> > > }
> > > /* Fallback/non-XDP mode: API user have elevated refcnt.
> > > *
> > > @@ -330,8 +331,7 @@ void __page_pool_put_page(struct page_pool
> > > *pool,
> > > * doing refcnt based recycle tricks, meaning another process
> > > * will be invoking put_page.
> > > */
> > > - __page_pool_clean_page(pool, page);
> > > - put_page(page);
> > > + __page_pool_return_page(pool, page);
> >
> > I think Jesper had a reason for calling them separately instead of
> > __page_pool_return_page + put_page() (which in fact does the same
> > thing).
> >
> > In the future he was planning on removing the
> > __page_pool_clean_page call from
> > there, since someone might call __page_pool_put_page() after
> > someone has called
> > __page_pool_clean_page()
>
> Yes. We need to work on removing this __page_pool_clean_page()
> call,
> to fulfill the plans of SKB returning/recycling page_pool pages.
>
> > Can we leave the calls there as-is?
>
> Yes, please.
>
Sure, i will drop this patch for now.
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