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Howlett" , Dave Chinner , "Paul E . McKenney" , Joel Fernandes , Oleksiy Avramchenko , "kexec@lists.infradead.org" Subject: Re: [PATCH v2 4/9] mm: vmalloc: Remove global vmap_area_root rb-tree Message-ID: References: <20230829081142.3619-1-urezki@gmail.com> <20230829081142.3619-5-urezki@gmail.com> <8939ea67-ca27-1aa5-dfff-37d78ad59bb8@nec.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8939ea67-ca27-1aa5-dfff-37d78ad59bb8@nec.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 X-Rspamd-Queue-Id: EE99140019 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 5tmiyetatehn36pi94tm3geofs6r6iz9 X-HE-Tag: 1694148212-318895 X-HE-Meta: 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 uSAedNm2 22XPMM3RzAHeTOid1i8YE0WuV/PjPXzHgTy99izCSgUq6BUaO89b+0FKe8g6IBrIDKkrjVR1U8EaSBWMKvQhMq47sV/m7bfmXAnkZ/ydM8++Iw6n8e0E1h+N7HOpZHDC0VqPDHFV5ljxDP1S8aN3UsRikK93nxL0nKJdLB1obT39BH9NVSGqBUAIEfI36W+Ac5vWzlOy8uIOCm4MxLHtjezbeh+Nze+uYLeEPOhyWSKKfQriBY6OS9gDEqk2XqnDpqTs13Pggva+k2TXOJxqFBSvhasrOUsugNYJH X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 09/08/23 at 01:51am, HAGIO KAZUHITO(萩尾 一仁) wrote: > On 2023/09/07 18:58, Baoquan He wrote: > > On 09/07/23 at 11:39am, Uladzislau Rezki wrote: > >> On Thu, Sep 07, 2023 at 10:17:39AM +0800, Baoquan He wrote: > >>> Add Kazu and Lianbo to CC, and kexec mailing list > >>> > >>> On 08/29/23 at 10:11am, Uladzislau Rezki (Sony) wrote: > >>>> Store allocated objects in a separate nodes. A va->va_start > >>>> address is converted into a correct node where it should > >>>> be placed and resided. An addr_to_node() function is used > >>>> to do a proper address conversion to determine a node that > >>>> contains a VA. > >>>> > >>>> Such approach balances VAs across nodes as a result an access > >>>> becomes scalable. Number of nodes in a system depends on number > >>>> of CPUs divided by two. The density factor in this case is 1/2. > >>>> > >>>> Please note: > >>>> > >>>> 1. As of now allocated VAs are bound to a node-0. It means the > >>>> patch does not give any difference comparing with a current > >>>> behavior; > >>>> > >>>> 2. The global vmap_area_lock, vmap_area_root are removed as there > >>>> is no need in it anymore. The vmap_area_list is still kept and > >>>> is _empty_. It is exported for a kexec only; > >>> > >>> I haven't taken a test, while accessing all nodes' busy tree to get > >>> va of the lowest address could severely impact kcore reading efficiency > >>> on system with many vmap nodes. People doing live debugging via > >>> /proc/kcore will get a little surprise. > >>> > >>> > >>> Empty vmap_area_list will break makedumpfile utility, Crash utility > >>> could be impactd too. I checked makedumpfile code, it relys on > >>> vmap_area_list to deduce the vmalloc_start value. > >>> > >> It is left part and i hope i fix it in v3. The problem here is > >> we can not give an opportunity to access to vmap internals from > >> outside. This is just not correct, i.e. you are not allowed to > >> access the list directly. > > > > Right. Thanks for the fix in v3, that is a relief of makedumpfile and > > crash. > > > > Hi Kazu, > > > > Meanwhile, I am thinking if we should evaluate the necessity of > > vmap_area_list in makedumpfile and Crash. In makedumpfile, we just use > > vmap_area_list to deduce VMALLOC_START. Wondering if we can export > > VMALLOC_START directly. Surely, the lowest va->va_start in vmap_area_list > > is a tighter low boundary of vmalloc area and can reduce unnecessary > > scanning below the lowest va. Not sure if this is the reason people > > decided to export vmap_area_list. > > The kernel commit acd99dbf5402 introduced the original vmlist entry to > vmcoreinfo, but there is no information about why it did not export > VMALLOC_START directly. > > If VMALLOC_START is exported directly to vmcoreinfo, I think it would be > enough for makedumpfile. Thanks for confirmation, Kazu. Then, below draft patch should be enough to export VMALLOC_START instead, and remove vmap_area_list. In order to get the base address of vmalloc area, constructing a vmap_area_list from multiple busy-tree seems not worth. diff --git a/Documentation/admin-guide/kdump/vmcoreinfo.rst b/Documentation/admin-guide/kdump/vmcoreinfo.rst index 599e8d3bcbc3..3cb1ea09ff26 100644 --- a/Documentation/admin-guide/kdump/vmcoreinfo.rst +++ b/Documentation/admin-guide/kdump/vmcoreinfo.rst @@ -65,11 +65,11 @@ Defines the beginning of the text section. In general, _stext indicates the kernel start address. Used to convert a virtual address from the direct kernel map to a physical address. -vmap_area_list --------------- +VMALLOC_START +------------- -Stores the virtual area list. makedumpfile gets the vmalloc start value -from this variable and its value is necessary for vmalloc translation. +Stores the base address of vmalloc area. makedumpfile gets this value and +its value is necessary for vmalloc translation. mem_map ------- diff --git a/arch/arm64/kernel/crash_core.c b/arch/arm64/kernel/crash_core.c index 66cde752cd74..2a24199a9b81 100644 --- a/arch/arm64/kernel/crash_core.c +++ b/arch/arm64/kernel/crash_core.c @@ -23,7 +23,6 @@ void arch_crash_save_vmcoreinfo(void) /* Please note VMCOREINFO_NUMBER() uses "%d", not "%x" */ vmcoreinfo_append_str("NUMBER(MODULES_VADDR)=0x%lx\n", MODULES_VADDR); vmcoreinfo_append_str("NUMBER(MODULES_END)=0x%lx\n", MODULES_END); - vmcoreinfo_append_str("NUMBER(VMALLOC_START)=0x%lx\n", VMALLOC_START); vmcoreinfo_append_str("NUMBER(VMALLOC_END)=0x%lx\n", VMALLOC_END); vmcoreinfo_append_str("NUMBER(VMEMMAP_START)=0x%lx\n", VMEMMAP_START); vmcoreinfo_append_str("NUMBER(VMEMMAP_END)=0x%lx\n", VMEMMAP_END); diff --git a/arch/riscv/kernel/crash_core.c b/arch/riscv/kernel/crash_core.c index 55f1d7856b54..5c39cedd2c5c 100644 --- a/arch/riscv/kernel/crash_core.c +++ b/arch/riscv/kernel/crash_core.c @@ -9,7 +9,6 @@ void arch_crash_save_vmcoreinfo(void) VMCOREINFO_NUMBER(phys_ram_base); vmcoreinfo_append_str("NUMBER(PAGE_OFFSET)=0x%lx\n", PAGE_OFFSET); - vmcoreinfo_append_str("NUMBER(VMALLOC_START)=0x%lx\n", VMALLOC_START); vmcoreinfo_append_str("NUMBER(VMALLOC_END)=0x%lx\n", VMALLOC_END); vmcoreinfo_append_str("NUMBER(VMEMMAP_START)=0x%lx\n", VMEMMAP_START); vmcoreinfo_append_str("NUMBER(VMEMMAP_END)=0x%lx\n", VMEMMAP_END); diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h index c720be70c8dd..91810b4e9510 100644 --- a/include/linux/vmalloc.h +++ b/include/linux/vmalloc.h @@ -253,7 +253,6 @@ extern long vread_iter(struct iov_iter *iter, const char *addr, size_t count); /* * Internals. Don't use.. */ -extern struct list_head vmap_area_list; extern __init void vm_area_add_early(struct vm_struct *vm); extern __init void vm_area_register_early(struct vm_struct *vm, size_t align); diff --git a/kernel/crash_core.c b/kernel/crash_core.c index 03a7932cde0a..91af87930770 100644 --- a/kernel/crash_core.c +++ b/kernel/crash_core.c @@ -617,7 +617,7 @@ static int __init crash_save_vmcoreinfo_init(void) VMCOREINFO_SYMBOL_ARRAY(swapper_pg_dir); #endif VMCOREINFO_SYMBOL(_stext); - VMCOREINFO_SYMBOL(vmap_area_list); + vmcoreinfo_append_str("NUMBER(VMALLOC_START)=0x%lx\n", VMALLOC_START); #ifndef CONFIG_NUMA VMCOREINFO_SYMBOL(mem_map); diff --git a/kernel/kallsyms_selftest.c b/kernel/kallsyms_selftest.c index b4cac76ea5e9..8a689b4ff4f9 100644 --- a/kernel/kallsyms_selftest.c +++ b/kernel/kallsyms_selftest.c @@ -89,7 +89,6 @@ static struct test_item test_items[] = { ITEM_DATA(kallsyms_test_var_data_static), ITEM_DATA(kallsyms_test_var_bss), ITEM_DATA(kallsyms_test_var_data), - ITEM_DATA(vmap_area_list), #endif }; diff --git a/mm/nommu.c b/mm/nommu.c index 7f9e9e5a0e12..8c6686176ebd 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -131,8 +131,6 @@ int follow_pfn(struct vm_area_struct *vma, unsigned long address, } EXPORT_SYMBOL(follow_pfn); -LIST_HEAD(vmap_area_list); - void vfree(const void *addr) { kfree(addr); diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 50d8239b82df..0a02633a9566 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -729,8 +729,7 @@ EXPORT_SYMBOL(vmalloc_to_pfn); static DEFINE_SPINLOCK(free_vmap_area_lock); -/* Export for kexec only */ -LIST_HEAD(vmap_area_list); + static bool vmap_initialized __read_mostly; /* -- 2.41.0