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[2003:cb:c70a:7e00:bb5b:b526:5b76:5824]) by smtp.gmail.com with ESMTPSA id o20-20020a1c7514000000b0039c4ec6fdacsm4549519wmc.40.2022.06.17.00.43.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 17 Jun 2022 00:43:34 -0700 (PDT) Message-ID: <186924ab-651f-71a1-93d2-3500a67dffee@redhat.com> Date: Fri, 17 Jun 2022 09:43:33 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH v2 2/2] mm: memory_hotplug: introduce SECTION_CANNOT_OPTIMIZE_VMEMMAP Content-Language: en-US To: Oscar Salvador Cc: Muchun Song , corbet@lwn.net, akpm@linux-foundation.org, paulmck@kernel.org, mike.kravetz@oracle.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, duanxiongchun@bytedance.com, smuchun@gmail.com References: <20220520025538.21144-1-songmuchun@bytedance.com> <20220520025538.21144-3-songmuchun@bytedance.com> <53024884-0182-df5f-9ca2-00652c64ce36@redhat.com> <24d5ec20-9c9e-93aa-11f4-c4619f51f7d1@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 17.06.22 07:46, 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) VmemmapSelfHosted, then the function names get nicer. > +#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)); > + struct page *memmap; > + > + memmap = sparse_decode_mem_map(ms->section_mem_map, > + pfn_to_section_nr(page_to_pfn(head))); Why can't we check the head page directly? Either I need more coffee or this can be simplified. > + > + if (PageVmemmap_self_hosted(memmap)) Maybe that's the right place for a comment, an ascii art, and how it is safe to only check the first vmemmap page due to alignment restrictions. > + 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 > + */ I think that comment can be dropped because the code does exactly that. > + 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 > > -- Thanks, David / dhildenb