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Message-ID: <YrBz5dBpb3XTZm5c@localhost.localdomain>
Date: Mon, 20 Jun 2022 15:19:33 +0200
From: Oscar Salvador <osalvador@...e.de>
To: Muchun Song <songmuchun@...edance.com>
Cc: akpm@...ux-foundation.org, corbet@....net, david@...hat.com,
mike.kravetz@...cle.com, paulmck@...nel.org,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, duanxiongchun@...edance.com, smuchun@...il.com
Subject: Re: [PATCH v5 2/2] mm: memory_hotplug: make hugetlb_optimize_vmemmap
compatible with memmap_on_memory
On Mon, Jun 20, 2022 at 07:06:16PM +0800, Muchun Song wrote:
> + /*
> + * The READ_ONCE() is used to stabilize *pmdp in a register or
> + * on the stack so that it will stop changing under the code.
> + * The only concurrent operation where it can be changed is
> + * split_vmemmap_huge_pmd() (*pmdp will be stable after this
> + * operation).
> + */
> + pmd = READ_ONCE(*pmdp);
> + if (pmd_leaf(pmd))
> + vmemmap_page = pmd_page(pmd) + pte_index(vaddr);
> + else
> + vmemmap_page = pte_page(*pte_offset_kernel(pmdp, vaddr));
I was about to suggest to get rid of the else branch because on x86_64
we can only allocate PMD_SIZE chunks when using an alternative allocator,
meaning that anything which is not a pmd_leaf can't be a PageVmemmapSelfHosted.
But then I went to check the other platform that supports memmap_on_memory (arm64),
and in there I can see that we fallback to populate basepages with altmap should
we fail to allocate a PMD_SIZE chunk.
> + /*
> + * Due to HugeTLB alignment requirements and the vmemmap pages
> + * being at the start of the hotplugged memory region in
> + * memory_hotplug.memmap_on_memory case. Checking any vmemmap
> + * page's vmemmap page if it is marked as VmemmapSelfHosted is
> + * sufficient.
> + *
> + * [ hotplugged memory ]
> + * [ section ][...][ section ]
> + * [ vmemmap ][ usable memory ]
> + * ^ | | |
> + * +---+ | |
> + * ^ | |
> + * +-------+ |
> + * ^ |
> + * +-------------------------------------------+
> + */
> + if (PageVmemmapSelfHosted(vmemmap_page))
> + return 0;
> + }
> +
> + return hugetlb_optimize_vmemmap_pages(h);
> +}
> +
> void hugetlb_vmemmap_free(struct hstate *h, struct page *head)
> {
> unsigned long vmemmap_addr = (unsigned long)head;
> unsigned long vmemmap_end, vmemmap_reuse, vmemmap_pages;
>
> - vmemmap_pages = hugetlb_optimize_vmemmap_pages(h);
> + vmemmap_pages = vmemmap_optimizable_pages(h, head);
> if (!vmemmap_pages)
> return;
>
> - if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)
> - return;
> -
> static_branch_inc(&hugetlb_optimize_vmemmap_key);
>
> vmemmap_addr += RESERVE_VMEMMAP_SIZE;
> @@ -199,10 +249,10 @@ static struct ctl_table hugetlb_vmemmap_sysctls[] = {
> static __init int hugetlb_vmemmap_sysctls_init(void)
> {
> /*
> - * If "memory_hotplug.memmap_on_memory" is enabled or "struct page"
> - * crosses page boundaries, the vmemmap pages cannot be optimized.
> + * If "struct page" crosses page boundaries, the vmemmap pages cannot
> + * be optimized.
> */
> - if (!mhp_memmap_on_memory() && is_power_of_2(sizeof(struct page)))
> + if (is_power_of_2(sizeof(struct page)))
> register_sysctl_init("vm", hugetlb_vmemmap_sysctls);
>
> return 0;
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 6662b86e9e64..3a59d4e97c03 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -43,30 +43,22 @@
> #include "shuffle.h"
>
> #ifdef CONFIG_MHP_MEMMAP_ON_MEMORY
> -static int memmap_on_memory_set(const char *val, const struct kernel_param *kp)
> -{
> - if (hugetlb_optimize_vmemmap_enabled())
> - return 0;
> - return param_set_bool(val, kp);
> -}
> -
> -static const struct kernel_param_ops memmap_on_memory_ops = {
> - .flags = KERNEL_PARAM_OPS_FL_NOARG,
> - .set = memmap_on_memory_set,
> - .get = param_get_bool,
> -};
> -
> /*
> * memory_hotplug.memmap_on_memory parameter
> */
> static bool memmap_on_memory __ro_after_init;
> -module_param_cb(memmap_on_memory, &memmap_on_memory_ops, &memmap_on_memory, 0444);
> +module_param(memmap_on_memory, bool, 0444);
> MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory hotplug");
>
> -bool mhp_memmap_on_memory(void)
> +static inline bool mhp_memmap_on_memory(void)
> {
> return memmap_on_memory;
> }
> +#else
> +static inline bool mhp_memmap_on_memory(void)
> +{
> + return false;
> +}
> #endif
>
> enum {
> @@ -1035,7 +1027,7 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
> struct zone *zone)
> {
> unsigned long end_pfn = pfn + nr_pages;
> - int ret;
> + int ret, i;
>
> ret = kasan_add_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages));
> if (ret)
> @@ -1043,6 +1035,9 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
>
> move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_UNMOVABLE);
>
> + for (i = 0; i < nr_pages; i++)
> + SetPageVmemmapSelfHosted(pfn_to_page(pfn + i));
> +
> /*
> * It might be that the vmemmap_pages fully span sections. If that is
> * the case, mark those sections online here as otherwise they will be
> --
> 2.11.0
>
>
--
Oscar Salvador
SUSE Labs
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