netdev - Re: [PATCH net-next v4 2/5] page_frag: unify gfp bits for order 3 page allocation

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Date: Fri, 02 Feb 2024 09:36:38 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Yunsheng Lin <linyunsheng@...wei.com>, davem@...emloft.net,
 kuba@...nel.org
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, Alexander Duyck
	 <alexanderduyck@...com>, Alexander Duyck <alexander.duyck@...il.com>, 
	"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 v4 2/5] page_frag: unify gfp bits for order 3
 page allocation

On Fri, 2024-02-02 at 10:10 +0800, Yunsheng Lin wrote:
> On 2024/2/1 21:16, Paolo Abeni wrote:
> 
> > from the __page_frag_cache_refill() allocator - which never accesses
> > the memory reserves.
> 
> I am not really sure I understand the above commemt.
> The semantic is the same as skb_page_frag_refill() as explained above
> as my understanding. Note that __page_frag_cache_refill() use 'gfp_mask'
> for allocating order 3 pages and use the original 'gfp' for allocating
> order 0 pages.

You are right! I got fooled misreading 'gfp' as 'gfp_mask' in there.

> > I'm unsure we want to propagate the __page_frag_cache_refill behavior
> > here, the current behavior could be required by some systems.
> > 
> > It looks like this series still leave the skb_page_frag_refill()
> > allocator alone, what about dropping this chunk, too? 
> 
> As explained above, I would prefer to keep it as it is as it seems
> to be quite obvious that we can avoid possible pressure for mm by
> not using memory reserve for order 3 pages as we have the fallback
> for order 0 pages.
> 
> Please let me know if there is anything obvious I missed.
> 

I still think/fear that behaviours changes here could have
subtle/negative side effects - even if I agree the change looks safe.

I think the series without this patch would still achieve its goals and
would be much more uncontroversial. What about move this patch as a
standalone follow-up?

Thanks!

Paolo