On Thu, Aug 01, 2019 at 08:41:53AM +0200, Michal Hocko wrote: > On Wed 31-07-19 16:44:50, Catalin Marinas wrote: > > On Tue, Jul 30, 2019 at 01:02:15PM -0700, Andrew Morton wrote: > > > On Sat, 27 Jul 2019 14:23:33 +0100 Catalin Marinas <catalin.marinas@xxxxxxx> wrote: > > > > Add mempool allocations for struct kmemleak_object and > > > > kmemleak_scan_area as slightly more resilient than kmem_cache_alloc() > > > > under memory pressure. Additionally, mask out all the gfp flags passed > > > > to kmemleak other than GFP_KERNEL|GFP_ATOMIC. > > > > > > > > A boot-time tuning parameter (kmemleak.mempool) is added to allow a > > > > different minimum pool size (defaulting to NR_CPUS * 4). > > > > > > btw, the checkpatch warnings are valid: > > > > > > WARNING: usage of NR_CPUS is often wrong - consider using cpu_possible(), num_possible_cpus(), for_each_possible_cpu(), etc > > > #70: FILE: mm/kmemleak.c:197: > > > +static int min_object_pool = NR_CPUS * 4; > > > > > > WARNING: usage of NR_CPUS is often wrong - consider using cpu_possible(), num_possible_cpus(), for_each_possible_cpu(), etc > > > #71: FILE: mm/kmemleak.c:198: > > > +static int min_scan_area_pool = NR_CPUS * 1; > > > > > > There can be situations where NR_CPUS is much larger than > > > num_possible_cpus(). Can we initialize these tunables within > > > kmemleak_init()? > > > > We could and, at least on arm64, cpu_possible_mask is already > > initialised at that point. However, that's a totally made up number. I > > think we would better go for a Kconfig option (defaulting to, say, 1024) > > similar to the CONFIG_DEBUG_KMEMLEAK_EARLY_LOG_SIZE and we grow it if > > people report better values in the future. > > If you really want/need to make this configurable then the command line > parameter makes more sense - think of distribution kernel users for > example. I doubt you'd have pre-built distribution kernels with kmemleak enabled. > But I am still not sure why this is really needed. The initial > size is a "made up" number of course. There is no good estimation to > make (without a crystal ball). The value might be increased based on > real life usage. We had a similar situation with the early log buffer (before slab is initialised), initially 400 which was good enough for my needs (embedded systems) but others had entirely different requirements. A configurable (cmdline, Kconfig) option would make it easier for people to change, especially if coupled with a meaningful suggestion in dmesg. Another option is to use the early log as an emergency pool after initialisation instead of freeing it (it's currently __initdata) and drop the mempool idea. I may give this a go, at least we only have a single Kconfig option. -- Catalin
