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Subject: Re: [PATCH v1 2/2] hugetlb: process multiple lists in
 gather_bootmem_prealloc_parallel
From: Muchun Song <muchun.song@linux.dev>
In-Reply-To: <20240213111347.3189206-3-gang.li@linux.dev>
Date: Tue, 13 Feb 2024 22:54:40 +0800
Cc: Andrew Morton <akpm@linux-foundation.org>,
 Steffen Klassert <steffen.klassert@secunet.com>,
 Daniel Jordan <daniel.m.jordan@oracle.com>,
 Jane Chu <jane.chu@oracle.com>,
 "Paul E . McKenney" <paulmck@kernel.org>,
 Randy Dunlap <rdunlap@infradead.org>,
 kernel test robot <lkp@intel.com>,
 Gang Li <ligang.bdlg@bytedance.com>,
 linux-kernel@vger.kernel.org,
 linux-mm@kvack.org
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Message-Id: <1B2A09F0-8F2B-426A-9D1D-6A39C3A6CF64@linux.dev>
References: <20240213111347.3189206-1-gang.li@linux.dev>
 <20240213111347.3189206-3-gang.li@linux.dev>
To: Gang Li <gang.li@linux.dev>


> On Feb 13, 2024, at 19:13, Gang Li <gang.li@linux.dev> wrote:
> 
> gather_bootmem_prealloc_node currently only process one list in
> huge_boot_pages array. So gather_bootmem_prealloc expects
> padata_do_multithreaded to run num_node_state(N_MEMORY) instances of
> gather_bootmem_prealloc_node to process all lists in huge_boot_pages.
> 
> This works well in current padata_do_multithreaded implementation.
> It guarantees that size/min_chunk <= thread num <= max_threads.
> 
> ```
> /* Ensure at least one thread when size < min_chunk. */
> nworks = max(job->size / max(job->min_chunk, job->align), 1ul);
> nworks = min(nworks, job->max_threads);
> 
> ps.nworks      = padata_work_alloc_mt(nworks, &ps, &works);
> ```
> 
> However, the comment of padata_do_multithreaded API only promises a
> maximum value for the number of threads and does not specify a
> minimum value. Which may pass multiple nodes to
> gather_bootmem_prealloc_node and only one node will be processed.
> 
> To avoid potential errors, introduce gather_bootmem_prealloc_parallel
> to handle the case where the number of threads does not meet the
> requirement of max_threads.
> 
> Fixes: 0306f03dcbd7 ("hugetlb: parallelize 1G hugetlb initialization")
> Signed-off-by: Gang Li <ligang.bdlg@bytedance.com>

Reviewed-by: Muchun Song <muchun.song@linux.dev>

Thanks.