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Date: Thu, 30 Nov 2023 17:00:52 +0800
From: Yunsheng Lin <>
To: Alexander H Duyck <>, David Howells
	<>, <>
CC: "David S. Miller" <>, Eric Dumazet
	<>, Jakub Kicinski <>, Paolo Abeni
	<>, Willem de Bruijn <>,
	David Ahern <>, Matthew Wilcox <>, Jens
 Axboe <>, <>,
	<>, Jeroen de Borst <>,
	Catherine Sullivan <>, Shailend Chand <>,
	Felix Fietkau <>, John Crispin <>, Sean Wang
	<>, Mark Lee <>, Lorenzo
 Bianconi <>, Matthias Brugger <>,
	AngeloGioacchino Del Regno <>, Keith
 Busch <>, Jens Axboe <>, Christoph Hellwig
	<>, Sagi Grimberg <>, Chaitanya Kulkarni
	<>, Andrew Morton <>,
	<>, <>,
Subject: Re: [PATCH net-next 03/12] mm: Make the page_frag_cache allocator
 alignment param a pow-of-2

On 2023/5/27 23:54, Alexander H Duyck wrote:
> On Wed, 2023-05-24 at 16:33 +0100, David Howells wrote:
>> Make the page_frag_cache allocator's alignment parameter a power of 2
>> rather than a mask and give a warning if it isn't.
>> This means that it's consistent with {napi,netdec}_alloc_frag_align() and
>> allows __{napi,netdev}_alloc_frag_align() to be removed.

I am trying to rmove the page frag implemetation in
vhost_net_page_frag_refill() by using page_frag_alloc_align(), and
I ended up having a simiar patch as this one.

> This goes against the original intention of these functions. One of the
> reasons why this is being used is because when somebody enables
> something like 2K jumbo frames they don't necessarily want to have to
> allocate 4K SLABs. Instead they can just add a bit of overhead and get
> almost twice the utilization out of an order 3 page.
> The requirement should only be cache alignment, not power of 2
> alignment. This isn't meant to be a slab allocator. We are just
> sectioning up pages to handle mixed workloads. In the case of
> networking we can end up getting everything from 60B packets, to 1514B
> in the standard cases. That was why we started sectioning up pages in
> the first place so putting a power of 2 requirement on it doens't fit
> our use case at all and is what we were trying to get away from with
> the SLAB allocators.

It seems that is_power_of_2() checking in this patch does not excluding
the non-align case if we are passing 'align' being 1, which means we still
can support the 'everything from 60B packets, to 1514B' case.

> .

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