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From: Oscar Salvador <osalvador@suse.de>
To: Muchun Song <songmuchun@bytedance.com>
Cc: corbet@lwn.net, mike.kravetz@oracle.com, tglx@linutronix.de,
	mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com,
	dave.hansen@linux.intel.com, luto@kernel.org,
	peterz@infradead.org, viro@zeniv.linux.org.uk,
	akpm@linux-foundation.org, paulmck@kernel.org,
	pawan.kumar.gupta@linux.intel.com, rdunlap@infradead.org,
	oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de,
	almasrymina@google.com, rientjes@google.com, willy@infradead.org,
	mhocko@suse.com, song.bao.hua@hisilicon.com, david@redhat.com,
	naoya.horiguchi@nec.com, joao.m.martins@oracle.com,
	duanxiongchun@bytedance.com, fam.zheng@bytedance.com,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v20 8/9] mm: memory_hotplug: disable memmap_on_memory when hugetlb_free_vmemmap enabled
Date: Tue, 20 Apr 2021 12:35:33 +0200
Message-ID: <YH6udU5rKmDcx5dY@localhost.localdomain> (raw)
In-Reply-To: <20210415084005.25049-9-songmuchun@bytedance.com>

On Thu, Apr 15, 2021 at 04:40:04PM +0800, Muchun Song wrote:
>  bool mhp_supports_memmap_on_memory(unsigned long size)
>  {
> +	bool supported;
>  	unsigned long nr_vmemmap_pages = size / PAGE_SIZE;
>  	unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
>  	unsigned long remaining_size = size - vmemmap_size;
> @@ -1011,11 +1012,18 @@ bool mhp_supports_memmap_on_memory(unsigned long size)
>  	 *	 altmap as an alternative source of memory, and we do not exactly
>  	 *	 populate a single PMD.
>  	 */
> -	return memmap_on_memory &&
> -	       IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) &&
> -	       size == memory_block_size_bytes() &&
> -	       IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
> -	       IS_ALIGNED(remaining_size, pageblock_nr_pages << PAGE_SHIFT);
> +	supported = memmap_on_memory &&
> +		    IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) &&
> +		    size == memory_block_size_bytes() &&
> +		    IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
> +		    IS_ALIGNED(remaining_size, pageblock_nr_pages << PAGE_SHIFT);
> +
> +	if (supported && is_hugetlb_free_vmemmap_enabled()) {
> +		pr_info("Cannot enable memory_hotplug.memmap_on_memory, it is not compatible with hugetlb_free_vmemmap\n");
> +		supported = false;
> +	}

I would not print anything and rather have

return memmap_on_memory &&
       !is_hugetlb_free_vmemmap_enabled &&
       IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) &&
       size == memory_block_size_bytes() &&
       IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
       IS_ALIGNED(remaining_size, pageblock_nr_pages << PAGE_SHIFT);

Documentation/admin-guide/kernel-parameters.txt already provides an
explanation on memory_hotplug.memmap_on_memory parameter that states
that the feature cannot be enabled when using hugetlb-vmemmap
optimization.

Users can always check whether the feature is enabled via
/sys/modules/memory_hotplug/parameters/memmap_on_memory.

Also, I did not check if it is, but if not, the fact about hugetlb-vmemmmap vs
hotplug-vmemmap should also be called out in the hugetlb-vmemmap kernel
parameter.

Thanks

-- 
Oscar Salvador
SUSE L3

  reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-15  8:39 [PATCH v20 0/9] Free some vmemmap pages of HugeTLB page Muchun Song
2021-04-15  8:39 ` [PATCH v20 1/9] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c Muchun Song
2021-04-15  8:39 ` [PATCH v20 2/9] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2021-04-15  8:39 ` [PATCH v20 3/9] mm: hugetlb: gather discrete indexes of tail page Muchun Song
2021-04-16 18:54   ` Mike Kravetz
2021-04-15  8:40 ` [PATCH v20 4/9] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page Muchun Song
2021-04-16 21:10   ` Mike Kravetz
2021-04-17  2:55     ` [External] " Muchun Song
2021-04-15  8:40 ` [PATCH v20 5/9] mm: hugetlb: defer freeing of HugeTLB pages Muchun Song
2021-04-16 23:55   ` Mike Kravetz
2021-04-17  4:13     ` [External] " Muchun Song
2021-04-15  8:40 ` [PATCH v20 6/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page Muchun Song
2021-04-19 23:19   ` Mike Kravetz
2021-04-20  8:46     ` [External] " Muchun Song
2021-04-20 17:48       ` Mike Kravetz
2021-04-21  3:42         ` Muchun Song
2021-04-15  8:40 ` [PATCH v20 7/9] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap Muchun Song
2021-04-19 23:41   ` Mike Kravetz
2021-04-15  8:40 ` [PATCH v20 8/9] mm: memory_hotplug: disable memmap_on_memory when hugetlb_free_vmemmap enabled Muchun Song
2021-04-20 10:35   ` Oscar Salvador [this message]
2021-04-21  3:41     ` [External] " Muchun Song
2021-04-21  7:33       ` Oscar Salvador
2021-04-21  9:06         ` Muchun Song
2021-04-15  8:40 ` [PATCH v20 9/9] mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate Muchun Song

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