linux-kernel - Re: [PATCH net-next 2/6] page_frag: unify gfp bits for order 3 page allocation

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Date: Fri, 05 Jan 2024 07:35:34 -0800
From: Alexander H Duyck <alexander.duyck@...il.com>
To: Yunsheng Lin <linyunsheng@...wei.com>, davem@...emloft.net,
 kuba@...nel.org,  pabeni@...hat.com
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, "Michael S.
 Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Eric Dumazet <edumazet@...gle.com>, 
 kvm@...r.kernel.org, virtualization@...ts.linux.dev, linux-mm@...ck.org
Subject: Re: [PATCH net-next 2/6] page_frag: unify gfp bits for order 3 page
 allocation

On Wed, 2024-01-03 at 17:56 +0800, Yunsheng Lin wrote:
> Currently there seems to be three page frag implementions
> which all try to allocate order 3 page, if that fails, it
> then fail back to allocate order 0 page, and each of them
> all allow order 3 page allocation to fail under certain
> condition by using specific gfp bits.
> 
> The gfp bits for order 3 page allocation are different
> between different implementation, __GFP_NOMEMALLOC is
> or'd to forbid access to emergency reserves memory for
> __page_frag_cache_refill(), but it is not or'd in other
> implementions, __GFP_DIRECT_RECLAIM is masked off to avoid
> direct reclaim in skb_page_frag_refill(), but it is not
> masked off in __page_frag_cache_refill().
> 
> This patch unifies the gfp bits used between different
> implementions by or'ing __GFP_NOMEMALLOC and masking off
> __GFP_DIRECT_RECLAIM for order 3 page allocation to avoid
> possible pressure for mm.
> 
> Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
> CC: Alexander Duyck <alexander.duyck@...il.com>
> ---
>  drivers/vhost/net.c | 2 +-
>  mm/page_alloc.c     | 4 ++--
>  net/core/sock.c     | 2 +-
>  3 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index f2ed7167c848..e574e21cc0ca 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -670,7 +670,7 @@ static bool vhost_net_page_frag_refill(struct vhost_net *net, unsigned int sz,
>  		/* Avoid direct reclaim but allow kswapd to wake */
>  		pfrag->page = alloc_pages((gfp & ~__GFP_DIRECT_RECLAIM) |
>  					  __GFP_COMP | __GFP_NOWARN |
> -					  __GFP_NORETRY,
> +					  __GFP_NORETRY | __GFP_NOMEMALLOC,
>  					  SKB_FRAG_PAGE_ORDER);
>  		if (likely(pfrag->page)) {
>  			pfrag->size = PAGE_SIZE << SKB_FRAG_PAGE_ORDER;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9a16305cf985..1f0b36dd81b5 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4693,8 +4693,8 @@ static struct page *__page_frag_cache_refill(struct page_frag_cache *nc,
>  	gfp_t gfp = gfp_mask;
>  
>  #if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
> -	gfp_mask |= __GFP_COMP | __GFP_NOWARN | __GFP_NORETRY |
> -		    __GFP_NOMEMALLOC;
> +	gfp_mask = (gfp_mask & ~__GFP_DIRECT_RECLAIM) |  __GFP_COMP |
> +		   __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC;
>  	page = alloc_pages_node(NUMA_NO_NODE, gfp_mask,
>  				PAGE_FRAG_CACHE_MAX_ORDER);
>  	nc->size = page ? PAGE_FRAG_CACHE_MAX_SIZE : PAGE_SIZE;
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 446e945f736b..d643332c3ee5 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -2900,7 +2900,7 @@ bool skb_page_frag_refill(unsigned int sz, struct page_frag *pfrag, gfp_t gfp)
>  		/* Avoid direct reclaim but allow kswapd to wake */
>  		pfrag->page = alloc_pages((gfp & ~__GFP_DIRECT_RECLAIM) |
>  					  __GFP_COMP | __GFP_NOWARN |
> -					  __GFP_NORETRY,
> +					  __GFP_NORETRY | __GFP_NOMEMALLOC,
>  					  SKB_FRAG_PAGE_ORDER);
>  		if (likely(pfrag->page)) {
>  			pfrag->size = PAGE_SIZE << SKB_FRAG_PAGE_ORDER;

Looks fine to me.

One thing you may want to consider would be to place this all in an
inline function that could just consolidate all the code.

Reviewed-by: Alexander Duyck <alexanderduyck@...com>