linux-kernel - Re: [PATCH] md/raid1: change r1conf->r1bio

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Message-ID: <35358897-5009-4843-8234-136bd5756e0b@gmail.com>
Date: Mon, 23 Jun 2025 11:18:03 +0800
From: Wang Jinchao <wangjinchao600@...il.com>
To: Yu Kuai <yukuai3@...wei.com>
Cc: linux-raid@...r.kernel.org, Song Liu <song@...nel.org>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] md/raid1: change r1conf->r1bio_pool to a pointer type

On 6/18/25 19:41, Wang Jinchao wrote:
>> In raid1_reshape(), newpool is a stack variable.
>> mempool_init() initializes newpool->wait with the stack address.
>> After assigning newpool to conf->r1bio_pool, the wait queue
>> need to be reinitialized, which is not ideal.
>> 
>> Change raid1_conf->r1bio_pool to a pointer type and
>> replace mempool_init() with mempool_create() to
>> avoid referencing a stack-based wait queue.
>>

>Can you also switch to kmalloc pool in this patch?

>Thanks,
>Kuai

Hi Kuai,

Comparing mempool_create_kmalloc_pool() and mempool_create(), the former 
requires the pool element size as a parameter, while the latter uses 
r1bio_pool_alloc() to allocate new elements, with the size calculated 
based on poolinfo->raid_disks.
The key point is poolinfo, which is used for both r1bio_pool and r1buf_pool.
If we change from mempool_create() to mempool_create_kmalloc_pool(), we 
would need to introduce a new concept, such as r1bio_pool_size, and 
store it somewhere. In this case, the original conf->poolinfo would lose 
its meaning and become just r1buf_poolinfo.
So I think keeping poolinfo is a better fit for the pool in RAID1.

By the way, I did not receive your email in my Gmail inbox; I found your 
message on lore.org. The last email I received from you was on June 16, 
so I am not sure what the problem is.
I also sent you an email mentioning that not using poolinfo makes 
rollback in raid1_reshape more difficult.
I wonder whether you received it, or maybe I missed your reply.

I am looking forward to your discussion. I want to gain a deeper 
understanding and contribute more to md/raid.

Thanks.