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Message-ID: <Yq1nTaV5B1WMFRtf@FVFYT0MHHV2J.usts.net>
Date: Sat, 18 Jun 2022 13:49:01 +0800
From: Muchun Song <songmuchun@...edance.com>
To: Oscar Salvador <osalvador@...e.de>
Cc: David Hildenbrand <david@...hat.com>, corbet@....net,
akpm@...ux-foundation.org, paulmck@...nel.org,
mike.kravetz@...cle.com, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
duanxiongchun@...edance.com, smuchun@...il.com
Subject: Re: [PATCH v2 2/2] mm: memory_hotplug: introduce
SECTION_CANNOT_OPTIMIZE_VMEMMAP
On Fri, Jun 17, 2022 at 07:46:53AM +0200, Oscar Salvador wrote:
> On Thu, Jun 16, 2022 at 09:30:33AM +0200, David Hildenbrand wrote:
> > IIRC, that was used to skip these patches on the offlining path before
> > we provided the ranges to offline_pages().
>
> Yeah, it was designed for that purpose back then.
>
> > I'd not mess with PG_reserved, and give them a clearer name, to not
> > confuse them with other, ordinary, vmemmap pages that are not
> > self-hosted (maybe in the future we might want to flag all vmemmap pages
> > with a new type?).
>
> Not sure whether a new type is really needed, or to put it another way, I
> cannot see the benefit.
>
> >
> > I'd just try reusing the flag PG_owner_priv_1. And eventually, flag all
> > (v)memmap pages with a type PG_memmap. However, the latter would be
> > optional and might not be strictly required
> >
> >
> > So what think could make sense is
> >
> > /* vmemmap pages that are self-hosted and cannot be optimized/freed. */
> > PG_vmemmap_self_hosted = PG_owner_priv_1,
>
> Sure, I just lightly tested the below, and seems to work, but not sure
> whether that is what you are referring to.
> @Munchun: thoughts?
>
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index e66f7aa3191d..a4556afd7bda 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 +633,10 @@ PAGEFLAG_FALSE(SkipKASanPoison, skip_kasan_poison)
> */
> __PAGEFLAG(Reported, reported, PF_NO_COMPOUND)
>
> +#ifdef CONFIG_MEMORY_HOTPLUG
> +PAGEFLAG(Vmemmap_self_hosted, vmemmap_self_hosted, PF_ANY)
> +#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..e2de7ed27e9e 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -101,6 +101,14 @@ 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;
> + struct mem_section *ms = __pfn_to_section(page_to_pfn(head));
Hi Oscar,
After more thinkging, I think here should be:
struct mem_section *ms = __pfn_to_section(ALIGN_DOWN(page_to_pfn(head), memory_block_size_bytes()));
Why?
[ hotplugged memory ]
[ section ][...][ section ]
[ vmemmap ][ usable memory ]
^ | | |
+---+ | |
^ | |
+--------+ |
^ |
+-------------------------------------------+
The page_to_pfn(head) can falls onto the non-1st section, actually, we desire
1st section which ->section_mem_map is the start vmemmap of the vmemmap.
If we align the page_to_pfn(head) with the start pfn of the hotplugged memory,
then we can simplify the code further.
unsigned long size = memory_block_size_bytes();
unsigned long pfn = ALIGN_DOWN(page_to_pfn(head), size);
if (pfn_valid(pfn) && PageVmemmapSelfHosted(pfn_to_page(pfn)))
return;
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 first section if
it is non-present.
Hopefully I am not wrong.
Thanks.
> + struct page *memmap;
> +
> + memmap = sparse_decode_mem_map(ms->section_mem_map,
> + pfn_to_section_nr(page_to_pfn(head)));
> +
> + if (PageVmemmap_self_hosted(memmap))
> + return;
>
> vmemmap_pages = hugetlb_optimize_vmemmap_pages(h);
> if (!vmemmap_pages)
> @@ -199,10 +207,10 @@ 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 1213d0c67a53..863966c2c6f1 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -45,8 +45,6 @@
> #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);
> }
>
> @@ -1032,6 +1030,7 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
> {
> unsigned long end_pfn = pfn + nr_pages;
> int ret;
> + int i;
>
> ret = kasan_add_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages));
> if (ret)
> @@ -1039,6 +1038,12 @@ 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);
>
> + /*
> + * Let us flag self-hosted memmap
> + */
> + for (i = 0; i < nr_pages; i++)
> + SetPageVmemmap_self_hosted(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
>
>
> --
> Oscar Salvador
> SUSE Labs
>
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