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 04/12] mm/hugetlb: Free the vmemmap pages associated with each HugeTLB page
Date: Thu, 10 Dec 2020 15:42:56 +0100 [thread overview]
Message-ID: <20201210144256.GB8538@localhost.localdomain> (raw)
In-Reply-To: <20201210035526.38938-5-songmuchun@bytedance.com>
On Thu, Dec 10, 2020 at 11:55:18AM +0800, Muchun Song wrote:
> The free_vmemmap_pages_per_hpage() which indicate that how many vmemmap
> pages associated with a HugeTLB page that can be freed to the buddy
> allocator just returns zero now, because all infrastructure is not
> ready. Once all the infrastructure is ready, we will rework this
> function to support the feature.
I would reword the above to:
"free_vmemmap_pages_per_hpage(), which indicates how many vmemmap
pages associated with a HugeTLB page can be freed, returns zero for
now, which means the feature is disabled.
We will enable it once all the infrastructure is there."
Or something along those lines.
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Overall this looks good to me, and it has seen a considerable
simplification, which is good.
Some nits/questions below:
> +#define vmemmap_hpage_addr_end(addr, end) \
> +({ \
> + unsigned long __boundary; \
> + __boundary = ((addr) + VMEMMAP_HPAGE_SIZE) & VMEMMAP_HPAGE_MASK; \
> + (__boundary - 1 < (end) - 1) ? __boundary : (end); \
> +})
Maybe add a little comment explaining what are you trying to get here.
> +/*
> + * Walk a vmemmap address to the pmd it maps.
> + */
> +static pmd_t *vmemmap_to_pmd(unsigned long addr)
> +{
> + pgd_t *pgd;
> + p4d_t *p4d;
> + pud_t *pud;
> + pmd_t *pmd;
> +
> + pgd = pgd_offset_k(addr);
> + if (pgd_none(*pgd))
> + return NULL;
> +
> + p4d = p4d_offset(pgd, addr);
> + if (p4d_none(*p4d))
> + return NULL;
> +
> + pud = pud_offset(p4d, addr);
> + if (pud_none(*pud))
> + return NULL;
> +
> + pmd = pmd_offset(pud, addr);
> + if (pmd_none(*pmd))
> + return NULL;
> +
> + return pmd;
> +}
I saw that some people suggested to put all the non-hugetlb vmemmap
functions under sparsemem-vmemmap.c, which makes some sense if some
feature is going to re-use this code somehow. (I am not sure if the
recent patches that take advantage of this feature for ZONE_DEVICE needs
something like this).
I do not have a strong opinion on this though.
> +static void vmemmap_reuse_pte_range(struct page *reuse, pte_t *pte,
> + unsigned long start, unsigned long end,
> + struct list_head *vmemmap_pages)
> +{
> + /*
> + * Make the tail pages are mapped with read-only to catch
> + * illegal write operation to the tail pages.
> + */
> + pgprot_t pgprot = PAGE_KERNEL_RO;
> + pte_t entry = mk_pte(reuse, pgprot);
> + unsigned long addr;
> +
> + for (addr = start; addr < end; addr += PAGE_SIZE, pte++) {
> + struct page *page;
> +
> + VM_BUG_ON(pte_none(*pte));
If it is none, page will be NULL and we will crash in the list_add
below?
> +static void vmemmap_remap_range(unsigned long start, unsigned long end,
> + struct list_head *vmemmap_pages)
> +{
> + pmd_t *pmd;
> + unsigned long next, addr = start;
> + struct page *reuse = NULL;
> +
> + VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE));
> + VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE));
> + VM_BUG_ON((start >> PUD_SHIFT) != (end >> PUD_SHIFT));
This last VM_BUG_ON, is to see if both fall under the same PUD table?
> +
> + pmd = vmemmap_to_pmd(addr);
> + BUG_ON(!pmd);
Which is the criteria you followed to make this BUG_ON and VM_BUG_ON
in the check from vmemmap_reuse_pte_range?
--
Oscar Salvador
SUSE L3
next prev parent reply other threads:[~2020-12-10 14:43 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 [this message]
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
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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