[PATCH net-next 0/4] net: Avoid the memory waste in some Ethernet drivers

[PATCH net-next 0/4] net: Avoid the memory waste in some Ethernet drivers

[Kevin Hao]

Hi,

In the current implementation of napi_alloc_frag(), it doesn't have any
align guarantee for the returned buffer address. We would have to use
some ugly workarounds to make sure that we can get a align buffer
address for some Ethernet drivers. This patch series tries to introduce
some helper functions to make sure that an align buffer is returned.
Then we can drop the ugly workarounds and avoid the unnecessary memory
waste.

Kevin Hao (4):
  mm: page_frag: Introduce page_frag_alloc_align()
  net: Introduce {netdev,napi}_alloc_frag_align()
  net: octeontx2: Use napi_alloc_frag_align() to avoid the memory waste
  net: dpaa2: Use napi_alloc_frag_align() to avoid the memory waste

 .../net/ethernet/freescale/dpaa2/dpaa2-eth.c  |  3 +-
 .../marvell/octeontx2/nic/otx2_common.c       |  3 +-
 include/linux/gfp.h                           |  3 ++
 include/linux/skbuff.h                        |  2 +
 mm/page_alloc.c                               | 12 +++++-
 net/core/skbuff.c                             | 40 ++++++++++++-------
 6 files changed, 43 insertions(+), 20 deletions(-)

-- 
2.29.2

[PATCH net-next 1/4] mm: page_frag: Introduce page_frag_alloc_align()

[Kevin Hao]

In the current implementation of page_frag_alloc(), it doesn't have
any align guarantee for the returned buffer address. But for some
hardwares they do require the DMA buffer to be aligned correctly,
so we would have to use some workarounds like below if the buffers
allocated by the page_frag_alloc() are used by these hardwares for
DMA.
    buf = page_frag_alloc(really_needed_size + align);
    buf = PTR_ALIGN(buf, align);

These codes seems ugly and would waste a lot of memories if the buffers
are used in a network driver for the TX/RX. So introduce
page_frag_alloc_align() to make sure that an aligned buffer address is
returned.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
---
 include/linux/gfp.h |  3 +++
 mm/page_alloc.c     | 12 ++++++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 6e479e9c48ce..e76e8618e9d7 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -583,6 +583,9 @@ extern void free_pages(unsigned long addr, unsigned int order);
 
 struct page_frag_cache;
 extern void __page_frag_cache_drain(struct page *page, unsigned int count);
+extern void *page_frag_alloc_align(struct page_frag_cache *nc,
+				   unsigned int fragsz, gfp_t gfp_mask,
+				   int align);
 extern void *page_frag_alloc(struct page_frag_cache *nc,
 			     unsigned int fragsz, gfp_t gfp_mask);
 extern void page_frag_free(void *addr);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 027f6481ba59..80f7c5f7d738 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5135,8 +5135,8 @@ void __page_frag_cache_drain(struct page *page, unsigned int count)
 }
 EXPORT_SYMBOL(__page_frag_cache_drain);
 
-void *page_frag_alloc(struct page_frag_cache *nc,
-		      unsigned int fragsz, gfp_t gfp_mask)
+void *page_frag_alloc_align(struct page_frag_cache *nc,
+		      unsigned int fragsz, gfp_t gfp_mask, int align)
 {
 	unsigned int size = PAGE_SIZE;
 	struct page *page;
@@ -5188,10 +5188,18 @@ void *page_frag_alloc(struct page_frag_cache *nc,
 	}
 
 	nc->pagecnt_bias--;
+	offset = align ? ALIGN_DOWN(offset, align) : offset;
 	nc->offset = offset;
 
 	return nc->va + offset;
 }
+EXPORT_SYMBOL(page_frag_alloc_align);
+
+void *page_frag_alloc(struct page_frag_cache *nc,
+		      unsigned int fragsz, gfp_t gfp_mask)
+{
+	return page_frag_alloc_align(nc, fragsz, gfp_mask, 0);
+}
 EXPORT_SYMBOL(page_frag_alloc);
 
 /*
-- 
2.29.2

Re: [PATCH net-next 1/4] mm: page_frag: Introduce page_frag_alloc_align()

[Jakub Kicinski]

On Sat, 23 Jan 2021 19:59:00 +0800 Kevin Hao wrote:
> +void *page_frag_alloc(struct page_frag_cache *nc,
> +		      unsigned int fragsz, gfp_t gfp_mask)
> +{
> +	return page_frag_alloc_align(nc, fragsz, gfp_mask, 0);
> +}
>  EXPORT_SYMBOL(page_frag_alloc);

Isn't it better to make this a static inline now?

Either way you'll need to repost after net is merged into net-next
(probably ~this Friday), please mark the posting as RFC before that.
Please make sure you CC the author of the code.

Re: [PATCH net-next 1/4] mm: page_frag: Introduce page_frag_alloc_align()

[Kevin Hao]

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On Sat, Jan 23, 2021 at 12:52:21PM -0800, Jakub Kicinski wrote:
> On Sat, 23 Jan 2021 19:59:00 +0800 Kevin Hao wrote:
> > +void *page_frag_alloc(struct page_frag_cache *nc,
> > +		      unsigned int fragsz, gfp_t gfp_mask)
> > +{
> > +	return page_frag_alloc_align(nc, fragsz, gfp_mask, 0);
> > +}
> >  EXPORT_SYMBOL(page_frag_alloc);
> 
> Isn't it better to make this a static inline now?

Sure. I will also inline the {netdev,napi}_alloc_frag().

> 
> Either way you'll need to repost after net is merged into net-next
> (probably ~this Friday), please mark the posting as RFC before that.

Sorry, I missed that. I will repost after the net is merged into net-next.

> Please make sure you CC the author of the code.

Will do.

Thanks,
Kevin

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Re: [PATCH net-next 1/4] mm: page_frag: Introduce page_frag_alloc_align()

[Vlastimil Babka]

On 1/23/21 12:59 PM, Kevin Hao wrote:
> In the current implementation of page_frag_alloc(), it doesn't have
> any align guarantee for the returned buffer address. But for some
> hardwares they do require the DMA buffer to be aligned correctly,
> so we would have to use some workarounds like below if the buffers
> allocated by the page_frag_alloc() are used by these hardwares for
> DMA.
>     buf = page_frag_alloc(really_needed_size + align);
>     buf = PTR_ALIGN(buf, align);
> 
> These codes seems ugly and would waste a lot of memories if the buffers
> are used in a network driver for the TX/RX. So introduce
> page_frag_alloc_align() to make sure that an aligned buffer address is
> returned.
> 
> Signed-off-by: Kevin Hao <haokexin@gmail.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

Agree with Jakub about static inline.

> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5135,8 +5135,8 @@ void __page_frag_cache_drain(struct page *page, unsigned int count)
>  }
>  EXPORT_SYMBOL(__page_frag_cache_drain);
>  
> -void *page_frag_alloc(struct page_frag_cache *nc,
> -		      unsigned int fragsz, gfp_t gfp_mask)
> +void *page_frag_alloc_align(struct page_frag_cache *nc,
> +		      unsigned int fragsz, gfp_t gfp_mask, int align)
>  {
>  	unsigned int size = PAGE_SIZE;
>  	struct page *page;
> @@ -5188,10 +5188,18 @@ void *page_frag_alloc(struct page_frag_cache *nc,
>  	}
>  
>  	nc->pagecnt_bias--;
> +	offset = align ? ALIGN_DOWN(offset, align) : offset;

We don't change offset if align == 0, so I'd go with simpler
if (align)
	offset = ...

>  	nc->offset = offset;
>  
>  	return nc->va + offset;
>  }
> +EXPORT_SYMBOL(page_frag_alloc_align);
> +
> +void *page_frag_alloc(struct page_frag_cache *nc,
> +		      unsigned int fragsz, gfp_t gfp_mask)
> +{
> +	return page_frag_alloc_align(nc, fragsz, gfp_mask, 0);
> +}
>  EXPORT_SYMBOL(page_frag_alloc);
>  
>  /*
>