linux-kernel - Re: [PATCH 1/1] hugetlb: fix CONFIG_PADATA dependency for non-SMP system

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Date: Thu, 8 Feb 2024 10:39:13 +0800
From: Muchun Song <muchun.song@...ux.dev>
To: Gang Li <gang.li@...ux.dev>
Cc: Gang Li <ligang.bdlg@...edance.com>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, Randy Dunlap <rdunlap@...radead.org>,
 kernel test robot <lkp@...el.com>
Subject: Re: [PATCH 1/1] hugetlb: fix CONFIG_PADATA dependency for non-SMP system



> On Feb 5, 2024, at 16:08, Gang Li <gang.li@...ux.dev> wrote:
> 
> On 2024/2/5 15:37, Muchun Song wrote:
>> Actually, I did not get it. Why the above code cannot work? The above
>> code already make it serialized in one call, right? What do I miss here?
>> Thanks.
> 
> PADATA consists of two distinct functionality:
> 
> One part is `padata_do_multithreaded`, which disregards
> order and simply divides tasks into several groups for parallel
> execution. My patch use `padata_do_multithreaded`.

OK. Since all users of PADATA of non-SMP case currently only use padata_do_multithreaded, it’s possible and easy to implement a variant of that in non-SMP case. It is not necessary to implement another functionality unless the only user of crypto/pcrypt.c does not depend on SMP in the future, at least now it’s dependent on SMP.

Thanks.

> 
> The other part is composed of a set of APIs that, while handling data in
> an out-of-order parallel manner, can eventually return the data with
> ordered sequence. Only `crypto/pcrypt.c` use them. I guess these APIs
> are designed specifically for `crypto/pcrypt.c`.
> ```
> padata_alloc
> padata_alloc_shell
> padata_do_parallel
> padata_do_serial
> padata_free_shell
> padata_free
> ```