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[90.235.20.237]) by smtp.gmail.com with ESMTPSA id x26-20020ac25dda000000b004fbc0c7218bsm257355lfq.118.2023.09.08.04.25.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 Sep 2023 04:25:32 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Fri, 8 Sep 2023 13:25:29 +0200 To: Baoquan He , k-hagio-ab@nec.com Cc: HAGIO =?utf-8?B?S0FaVUhJVE8o6JCp5bC+44CA5LiA5LuBKQ==?= , Uladzislau Rezki , "lijiang@redhat.com" , "linux-mm@kvack.org" , Andrew Morton , LKML , Lorenzo Stoakes , Christoph Hellwig , Matthew Wilcox , "Liam R . 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> <1d613b25-58d8-375b-6ef4-b27bc9b735e3@nec.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 08, 2023 at 02:44:56PM +0800, Baoquan He wrote: > On 09/08/23 at 05:01am, HAGIO KAZUHITO(萩尾 一仁) wrote: > > On 2023/09/08 13:43, Baoquan He wrote: > > > 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. > > > > also the following entries can be removed. > > > > VMCOREINFO_OFFSET(vmap_area, va_start); > > VMCOREINFO_OFFSET(vmap_area, list); > > Right, they are useless now. I updated to remove them in below patch. > > From a867fada34fd9e96528fcc5e72ae50b3b5685015 Mon Sep 17 00:00:00 2001 > From: Baoquan He > Date: Fri, 8 Sep 2023 11:53:22 +0800 > Subject: [PATCH] mm/vmalloc: remove vmap_area_list > Content-type: text/plain > > Earlier, vmap_area_list is exported to vmcoreinfo so that makedumpfile > get the base address of vmalloc area. Now, vmap_area_list is empty, so > export VMALLOC_START to vmcoreinfo instead, and remove vmap_area_list. > > Signed-off-by: Baoquan He > --- > Documentation/admin-guide/kdump/vmcoreinfo.rst | 8 ++++---- > arch/arm64/kernel/crash_core.c | 1 - > arch/riscv/kernel/crash_core.c | 1 - > include/linux/vmalloc.h | 1 - > kernel/crash_core.c | 4 +--- > kernel/kallsyms_selftest.c | 1 - > mm/nommu.c | 2 -- > mm/vmalloc.c | 3 +-- > 8 files changed, 6 insertions(+), 15 deletions(-) > > diff --git a/Documentation/admin-guide/kdump/vmcoreinfo.rst b/Documentation/admin-guide/kdump/vmcoreinfo.rst > index 599e8d3bcbc3..c11bd4b1ceb1 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 > +since 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..a9faaf7e5f7d 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); > @@ -658,8 +658,6 @@ static int __init crash_save_vmcoreinfo_init(void) > VMCOREINFO_OFFSET(free_area, free_list); > VMCOREINFO_OFFSET(list_head, next); > VMCOREINFO_OFFSET(list_head, prev); > - VMCOREINFO_OFFSET(vmap_area, va_start); > - VMCOREINFO_OFFSET(vmap_area, list); > VMCOREINFO_LENGTH(zone.free_area, MAX_ORDER + 1); > log_buf_vmcoreinfo_setup(); > VMCOREINFO_LENGTH(free_area.free_list, MIGRATE_TYPES); > 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 > Appreciate for your great input. This patch can go as standalone with slight commit message updating or i can take it and send it out as part of v3. Either way i am totally fine. What do you prefer? Thank you! -- Uladzislau Rezki