linux-kernel - Re: [PATCH v2] mm: alloc_pages_bulk: remove assumption of populating only NULL elements

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Message-ID: <c5cdd730-1e11-4440-849d-8841b5ce86ef@huawei.com>
Date: Wed, 12 Mar 2025 20:05:51 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>, NeilBrown <neilb@...e.de>
CC: Yunsheng Lin <yunshenglin0825@...il.com>, Dave Chinner
	<david@...morbit.com>, Yishai Hadas <yishaih@...dia.com>, Jason Gunthorpe
	<jgg@...pe.ca>, Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
	Kevin Tian <kevin.tian@...el.com>, Alex Williamson
	<alex.williamson@...hat.com>, Chris Mason <clm@...com>, Josef Bacik
	<josef@...icpanda.com>, David Sterba <dsterba@...e.com>, Gao Xiang
	<xiang@...nel.org>, Chao Yu <chao@...nel.org>, Yue Hu <zbestahu@...il.com>,
	Jeffle Xu <jefflexu@...ux.alibaba.com>, Sandeep Dhavale <dhavale@...gle.com>,
	Carlos Maiolino <cem@...nel.org>, "Darrick J. Wong" <djwong@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, Jesper Dangaard Brouer
	<hawk@...nel.org>, Ilias Apalodimas <ilias.apalodimas@...aro.org>, "David S.
 Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub
 Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman
	<horms@...nel.org>, Trond Myklebust <trondmy@...nel.org>, Anna Schumaker
	<anna@...nel.org>, Chuck Lever <chuck.lever@...cle.com>, Jeff Layton
	<jlayton@...nel.org>, Olga Kornievskaia <okorniev@...hat.com>, Dai Ngo
	<Dai.Ngo@...cle.com>, Tom Talpey <tom@...pey.com>, Luiz Capitulino
	<luizcap@...hat.com>, Mel Gorman <mgorman@...hsingularity.net>,
	<kvm@...r.kernel.org>, <virtualization@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, <linux-btrfs@...r.kernel.org>,
	<linux-erofs@...ts.ozlabs.org>, <linux-xfs@...r.kernel.org>,
	<linux-mm@...ck.org>, <netdev@...r.kernel.org>, <linux-nfs@...r.kernel.org>
Subject: Re: [PATCH v2] mm: alloc_pages_bulk: remove assumption of populating
 only NULL elements

On 2025/3/12 9:45, Gao Xiang wrote:
> 
> 
> On 2025/3/12 06:55, NeilBrown wrote:
>> On Mon, 10 Mar 2025, Gao Xiang wrote:
>>>
>>>    - Your new api covers narrow cases compared to the existing
>>>      api, although all in-tree callers may be converted
>>>      properly, but it increases mental burden of all users.
>>>      And maybe complicate future potential users again which
>>>      really have to "check NULL elements in the middle of page
>>>      bulk allocating" again.
>>
>> I think that the current API adds a mental burden for most users.  For
>> most users, their code would be much cleaner if the interface accepted
>> an uninitialised array with length, and were told how many pages had
>> been stored in that array.> A (very) few users benefit from the complexity.  So having two
>> interfaces, one simple and one full-featured, makes sense.

Thanks for the above clear summarization.

> 
> Ok, I think for this part, diferrent people has different
> perference on API since there is no absolutely right and
> wrong in the API design area.
> 
> But I have no interest to follow this for now.

Just to be clearer, as erofs seems to be able to be changed to
use a simple interface, do you prefer to keep using the full-featured
interface or change to use the simple interface?

> 
> Thanks,
> Gao Xiang