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, Kazu
