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,
mchehab+huawei@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,
duanxiongchun@bytedance.com, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v8 06/12] mm/hugetlb: Allocate the vmemmap pages associated with each HugeTLB page
Date: Fri, 11 Dec 2020 10:35:23 +0100 [thread overview]
Message-ID: <20201211093517.GA22210@linux> (raw)
In-Reply-To: <20201210035526.38938-7-songmuchun@bytedance.com>
On Thu, Dec 10, 2020 at 11:55:20AM +0800, Muchun Song wrote:
> When we free a HugeTLB page to the buddy allocator, we should allocate the
> vmemmap pages associated with it. We can do that in the __free_hugepage()
"vmemmap pages that describe the range" would look better to me, but it is ok.
> +#define GFP_VMEMMAP_PAGE \
> + (GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_HIGH | __GFP_NOWARN)
>
> #ifndef VMEMMAP_HPAGE_SHIFT
> #define VMEMMAP_HPAGE_SHIFT HPAGE_SHIFT
> @@ -197,6 +200,11 @@
> (__boundary - 1 < (end) - 1) ? __boundary : (end); \
> })
>
> +typedef void (*vmemmap_remap_pte_func_t)(struct page *reuse, pte_t *pte,
> + unsigned long start, unsigned long end,
> + void *priv);
Any reason to not have defined GFP_VMEMMAP_PAGE and the new typedef into
hugetlb_vmemmap.h?
> +static void vmemmap_restore_pte_range(struct page *reuse, pte_t *pte,
> + unsigned long start, unsigned long end,
> + void *priv)
> +{
> + pgprot_t pgprot = PAGE_KERNEL;
> + void *from = page_to_virt(reuse);
> + unsigned long addr;
> + struct list_head *pages = priv;
[...]
> +
> + /*
> + * Make sure that any data that writes to the @to is made
> + * visible to the physical page.
> + */
> + flush_kernel_vmap_range(to, PAGE_SIZE);
Correct me if I am wrong, but flush_kernel_vmap_range is a NOOP under arches which
do not have ARCH_HAS_FLUSH_KERNEL_DCACHE_PAGE.
Since we only enable support for x86_64, and x86_64 is one of those arches,
could we remove this, and introduced later on in case we enable this feature
on an arch that needs it?
I am not sure if you need to flush the range somehow, as you did in
vmemmap_remap_range.
> +retry:
> + page = alloc_page(GFP_VMEMMAP_PAGE);
> + if (unlikely(!page)) {
> + msleep(100);
> + /*
> + * We should retry infinitely, because we cannot
> + * handle allocation failures. Once we allocate
> + * vmemmap pages successfully, then we can free
> + * a HugeTLB page.
> + */
> + goto retry;
I think this is the trickiest part.
With 2MB HugeTLB pages we only need 6 pages, but with 1GB, the number of pages
we need to allocate increases significantly (4088 pages IIRC).
And you are using __GFP_HIGH, which will allow us to use more memory (by
cutting down the watermark), but it might lead to putting the system
on its knees wrt. memory.
And yes, I know that once we allocate the 4088 pages, 1GB gets freed, but
still.
I would like to hear Michal's thoughts on this one, but I wonder if it makes
sense to not let 1GB-HugeTLB pages be freed.
--
Oscar Salvador
SUSE L3
next prev parent reply other threads:[~2020-12-11 9:37 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-10 3:55 [PATCH v8 00/12] Free some vmemmap pages of HugeTLB page Muchun Song
2020-12-10 3:55 ` [PATCH v8 01/12] mm/memory_hotplug: Factor out bootmem core functions to bootmem_info.c Muchun Song
2020-12-10 3:55 ` [PATCH v8 02/12] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2020-12-10 3:55 ` [PATCH v8 03/12] mm/bootmem_info: Introduce free_bootmem_page helper Muchun Song
2020-12-10 14:15 ` Oscar Salvador
2020-12-10 15:22 ` [External] " Muchun Song
2020-12-10 15:26 ` Muchun Song
2020-12-10 3:55 ` [PATCH v8 04/12] mm/hugetlb: Free the vmemmap pages associated with each HugeTLB page Muchun Song
2020-12-10 14:42 ` Oscar Salvador
2020-12-10 14:44 ` Oscar Salvador
2020-12-10 15:58 ` [External] " Muchun Song
2020-12-10 15:57 ` Muchun Song
2020-12-10 3:55 ` [PATCH v8 05/12] mm/hugetlb: Defer freeing of HugeTLB pages Muchun Song
2020-12-10 3:55 ` [PATCH v8 06/12] mm/hugetlb: Allocate the vmemmap pages associated with each HugeTLB page Muchun Song
2020-12-11 9:35 ` Oscar Salvador [this message]
2020-12-11 10:52 ` David Hildenbrand
2020-12-11 13:01 ` [External] " Muchun Song
2020-12-10 3:55 ` [PATCH v8 07/12] mm/hugetlb: Set the PageHWPoison to the raw error page Muchun Song
2020-12-10 11:11 ` Muchun Song
2020-12-11 13:36 ` Oscar Salvador
2020-12-11 14:08 ` [External] " Muchun Song
2020-12-10 3:55 ` [PATCH v8 08/12] mm/hugetlb: Flush work when dissolving hugetlb page Muchun Song
2020-12-10 3:55 ` [PATCH v8 09/12] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap Muchun Song
2020-12-10 10:04 ` Oscar Salvador
2020-12-10 12:26 ` [External] " Muchun Song
2020-12-10 3:55 ` [PATCH v8 10/12] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
2020-12-10 10:15 ` Oscar Salvador
2020-12-10 12:32 ` [External] " Muchun Song
2020-12-10 3:55 ` [PATCH v8 11/12] mm/hugetlb: Gather discrete indexes of tail page Muchun Song
2020-12-10 3:55 ` [PATCH v8 12/12] mm/hugetlb: Optimize the code with the help of the compiler Muchun Song
2020-12-10 10:25 ` Oscar Salvador
2020-12-10 12:14 ` [External] " Muchun Song
2020-12-10 13:16 ` Oscar Salvador
2020-12-10 13:29 ` Muchun Song
2020-12-10 16:19 ` Muchun Song
2020-12-10 9:18 ` [PATCH v8 00/12] Free some vmemmap pages of HugeTLB page Oscar Salvador
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