netdev - Re: [PATCH net-next 03/12] mm: Make the page_frag_cache allocator alignment param a pow-of-2

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Date: Thu, 30 Nov 2023 17:00:52 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Alexander H Duyck <alexander.duyck@...il.com>, David Howells
	<dhowells@...hat.com>, <netdev@...r.kernel.org>
CC: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	David Ahern <dsahern@...nel.org>, Matthew Wilcox <willy@...radead.org>, Jens
 Axboe <axboe@...nel.dk>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, Jeroen de Borst <jeroendb@...gle.com>,
	Catherine Sullivan <csully@...gle.com>, Shailend Chand <shailend@...gle.com>,
	Felix Fietkau <nbd@....name>, John Crispin <john@...ozen.org>, Sean Wang
	<sean.wang@...iatek.com>, Mark Lee <Mark-MC.Lee@...iatek.com>, Lorenzo
 Bianconi <lorenzo@...nel.org>, Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Keith
 Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>, Christoph Hellwig
	<hch@....de>, Sagi Grimberg <sagi@...mberg.me>, Chaitanya Kulkarni
	<kch@...dia.com>, Andrew Morton <akpm@...ux-foundation.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-mediatek@...ts.infradead.org>,
	<linux-nvme@...ts.infradead.org>
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.

> 
> .
>