linux-kernel - Re: [PATCH net-next v1 00/12] First try to replace page_frag with page_frag

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Message-ID: <CAKgT0Uex+e_g9nyqk6DiB03U4zs_A1z2LoztHnpYbJ9LPm=NFA@mail.gmail.com>
Date: Sun, 7 Apr 2024 10:02:45 -0700
From: Alexander Duyck <alexander.duyck@...il.com>
To: Yunsheng Lin <linyunsheng@...wei.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, 
	linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org, 
	bpf@...r.kernel.org
Subject: Re: [PATCH net-next v1 00/12] First try to replace page_frag with page_frag_cache

On Sun, Apr 7, 2024 at 6:10 AM Yunsheng Lin <linyunsheng@...wei.com> wrote:
>
> After [1], Only there are two implementations for page frag:
>
> 1. mm/page_alloc.c: net stack seems to be using it in the
>    rx part with 'struct page_frag_cache' and the main API
>    being page_frag_alloc_align().
> 2. net/core/sock.c: net stack seems to be using it in the
>    tx part with 'struct page_frag' and the main API being
>    skb_page_frag_refill().
>
> This patchset tries to unfiy the page frag implementation
> by replacing page_frag with page_frag_cache for sk_page_frag()
> first. net_high_order_alloc_disable_key for the implementation
> in net/core/sock.c doesn't seems matter that much now have
> have pcp support for high-order pages in commit 44042b449872
> ("mm/page_alloc: allow high-order pages to be stored on the
> per-cpu lists").
>
> As the related change is mostly related to networking, so
> targeting the net-next. And will try to replace the rest
> of page_frag in the follow patchset.
>
> After this patchset, we are not only able to unify the page
> frag implementation a little, but seems able to have about
> 0.5+% performance boost testing by using the vhost_net_test
> introduced in [1] and page_frag_test.ko introduced in this
> patch.

One question that jumps out at me for this is "why?". No offense but
this is a pretty massive set of changes with over 1400 additions and
500+ deletions and I can't help but ask why, and this cover page
doesn't give me any good reason to think about accepting this set.
What is meant to be the benefit to the community for adding this? All
I am seeing is a ton of extra code to have to review as this
unification is adding an additional 1000+ lines without a good
explanation as to why they are needed.

Also I wouldn't bother mentioning the 0.5+% performance gain as a
"bonus". Changes of that amount usually mean it is within the margin
of error. At best it likely means you haven't introduced a noticeable
regression.