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Message-ID: <YrAgUtV6wD6CIrad@FVFYT0MHHV2J.usts.net>
Date: Mon, 20 Jun 2022 15:22:58 +0800
From: Muchun Song <songmuchun@...edance.com>
To: akpm@...ux-foundation.org, corbet@....net, david@...hat.com,
mike.kravetz@...cle.com, osalvador@...e.de, paulmck@...nel.org
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, duanxiongchun@...edance.com, smuchun@...il.com
Subject: Re: [PATCH v4 2/2] mm: memory_hotplug: make hugetlb_optimize_vmemmap
compatible with memmap_on_memory
On Sun, Jun 19, 2022 at 09:38:51PM +0800, Muchun Song wrote:
> For now, the feature of hugetlb_free_vmemmap is not compatible with the
> feature of memory_hotplug.memmap_on_memory, and hugetlb_free_vmemmap
> takes precedence over memory_hotplug.memmap_on_memory. However, someone
> wants to make memory_hotplug.memmap_on_memory takes precedence over
> hugetlb_free_vmemmap since memmap_on_memory makes it more likely to
> succeed memory hotplug in close-to-OOM situations. So the decision
> of making hugetlb_free_vmemmap take precedence is not wise and elegant.
> The proper approach is to have hugetlb_vmemmap.c do the check whether
> the section which the HugeTLB pages belong to can be optimized. If
> the section's vmemmap pages are allocated from the added memory block
> itself, hugetlb_free_vmemmap should refuse to optimize the vmemmap,
> otherwise, do the optimization. Then both kernel parameters are
> compatible. So this patch introduces VmemmapSelfHosted to mask any
> non-optimizable vmemmap pages. The hugetlb_vmemmap can use this flag
> to detect if a vmemmap page can be optimized.
>
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Co-developed-by: Oscar Salvador <osalvador@...e.de>
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 22 +++++------
> Documentation/admin-guide/sysctl/vm.rst | 5 +--
> include/linux/memory_hotplug.h | 9 -----
> include/linux/page-flags.h | 11 ++++++
> mm/hugetlb_vmemmap.c | 52 +++++++++++++++++++++----
> mm/memory_hotplug.c | 27 ++++++-------
> 6 files changed, 79 insertions(+), 47 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 8090130b544b..d740e2ed0e61 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1722,9 +1722,11 @@
> Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
> the default is on.
>
> - This is not compatible with memory_hotplug.memmap_on_memory.
> - If both parameters are enabled, hugetlb_free_vmemmap takes
> - precedence over memory_hotplug.memmap_on_memory.
> + Note that the vmemmap pages may be allocated from the added
> + memory block itself when memory_hotplug.memmap_on_memory is
> + enabled, those vmemmap pages cannot be optimized even if this
> + feature is enabled. Other vmemmap pages not allocated from
> + the added memory block itself do not be affected.
>
> hung_task_panic=
> [KNL] Should the hung task detector generate panics.
> @@ -3069,10 +3071,12 @@
> [KNL,X86,ARM] Boolean flag to enable this feature.
> Format: {on | off (default)}
> When enabled, runtime hotplugged memory will
> - allocate its internal metadata (struct pages)
> - from the hotadded memory which will allow to
> - hotadd a lot of memory without requiring
> - additional memory to do so.
> + allocate its internal metadata (struct pages,
> + those vmemmap pages cannot be optimized even
> + if hugetlb_free_vmemmap is enabled) from the
> + hotadded memory which will allow to hotadd a
> + lot of memory without requiring additional
> + memory to do so.
> This feature is disabled by default because it
> has some implication on large (e.g. GB)
> allocations in some configurations (e.g. small
> @@ -3082,10 +3086,6 @@
> Note that even when enabled, there are a few cases where
> the feature is not effective.
>
> - This is not compatible with hugetlb_free_vmemmap. If
> - both parameters are enabled, hugetlb_free_vmemmap takes
> - precedence over memory_hotplug.memmap_on_memory.
> -
> memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest
> Format: <integer>
> default : 0 <disable>
> diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
> index 5c9aa171a0d3..d7374a1e8ac9 100644
> --- a/Documentation/admin-guide/sysctl/vm.rst
> +++ b/Documentation/admin-guide/sysctl/vm.rst
> @@ -565,9 +565,8 @@ See Documentation/admin-guide/mm/hugetlbpage.rst
> hugetlb_optimize_vmemmap
> ========================
>
> -This knob is not available when memory_hotplug.memmap_on_memory (kernel parameter)
> -is configured or the size of 'struct page' (a structure defined in
> -include/linux/mm_types.h) is not power of two (an unusual system config could
> +This knob is not available when the size of 'struct page' (a structure defined
> +in include/linux/mm_types.h) is not power of two (an unusual system config could
> result in this).
>
> Enable (set to 1) or disable (set to 0) the feature of optimizing vmemmap pages
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 20d7edf62a6a..e0b2209ab71c 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -351,13 +351,4 @@ void arch_remove_linear_mapping(u64 start, u64 size);
> extern bool mhp_supports_memmap_on_memory(unsigned long size);
> #endif /* CONFIG_MEMORY_HOTPLUG */
>
> -#ifdef CONFIG_MHP_MEMMAP_ON_MEMORY
> -bool mhp_memmap_on_memory(void);
> -#else
> -static inline bool mhp_memmap_on_memory(void)
> -{
> - return false;
> -}
> -#endif
> -
> #endif /* __LINUX_MEMORY_HOTPLUG_H */
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index e66f7aa3191d..2aa5dcbfe468 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -193,6 +193,11 @@ enum pageflags {
>
> /* Only valid for buddy pages. Used to track pages that are reported */
> PG_reported = PG_uptodate,
> +
> +#ifdef CONFIG_MEMORY_HOTPLUG
> + /* For self-hosted memmap pages */
> + PG_vmemmap_self_hosted = PG_owner_priv_1,
> +#endif
> };
>
> #define PAGEFLAGS_MASK ((1UL << NR_PAGEFLAGS) - 1)
> @@ -628,6 +633,12 @@ PAGEFLAG_FALSE(SkipKASanPoison, skip_kasan_poison)
> */
> __PAGEFLAG(Reported, reported, PF_NO_COMPOUND)
>
> +#ifdef CONFIG_MEMORY_HOTPLUG
> +PAGEFLAG(VmemmapSelfHosted, vmemmap_self_hosted, PF_ANY)
> +#else
> +PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted)
> +#endif
> +
> /*
> * On an anonymous page mapped into a user virtual memory area,
> * page->mapping points to its anon_vma, not to a struct address_space;
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index 1089ea8a9c98..73bfbb47f6a4 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -10,7 +10,7 @@
> */
> #define pr_fmt(fmt) "HugeTLB: " fmt
>
> -#include <linux/memory_hotplug.h>
> +#include <linux/memory.h>
> #include "hugetlb_vmemmap.h"
>
> /*
> @@ -97,18 +97,54 @@ int hugetlb_vmemmap_alloc(struct hstate *h, struct page *head)
> return ret;
> }
>
> +static unsigned int vmemmap_optimizable_pages(struct hstate *h,
> + struct page *head)
> +{
> + if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)
> + return 0;
> +
> + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {
> + unsigned long pfn = page_to_pfn(head);
> +
> + /*
> + * 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 the first
> + * vmemmap page's vmemmap if it is marked as VmemmapSelfHosted
> + * is sufficient.
> + *
> + * [ hotplugged memory ]
> + * [ section ][...][ section ]
> + * [ vmemmap ][ usable memory ]
> + * ^ | | |
> + * +---+ | |
> + * ^ | |
> + * +-------+ |
> + * ^ |
> + * +-------------------------------------------+
> + *
> + * Hotplugged memory block never has non-present sections, while
> + * boot memory block can have one or more. So pfn_valid() is
> + * used to filter out the non-present section which also cannot
> + * be memmap_on_memory.
> + */
> + pfn = ALIGN_DOWN(pfn, PHYS_PFN(memory_block_size_bytes()));
> + if (pfn_valid(pfn) && PageVmemmapSelfHosted(pfn_to_page(pfn)))
Although it works, I think PageVmemmapSelfHosted() check for the 1st pfn's
vmemmap page is not always reliable. Since we reused PG_owner_priv_1
as PG_vmemmap_self_hosted, the test is noly reliable for vmemmap page's
vmemmap page. Other non-vmemmap page can be flagged with PG_owner_priv_1.
So this check can be false-positive. Maybe the following code snippet is
the solution.
Any thoughts? Oscar or David.
+ if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {
+ pmd_t *pmdp, pmd;
+ struct page *vmemmap_page;
+ unsigned long vaddr = (unsigned long)head;
+
+ pmdp = pmd_off_k(vaddr);
+ /*
+ * The READ_ONCE() is used to stabilize *pmdp in a register or
+ * on the stack so that it will stop changing under the code.
+ */
+ 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));
+ /*
+ * 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 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 +235,10 @@ 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
>
>
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