On Thu, Feb 04, 2021 at 02:04:27PM -0800, Paul E. McKenney wrote: > On Fri, Jan 29, 2021 at 09:05:05PM +0100, Uladzislau Rezki (Sony) wrote: > > Running an rcuscale stress-suite can lead to "Out of memory" > > of a system. This can happen under high memory pressure with > > a small amount of physical memory. > > > > For example a KVM test configuration with 64 CPUs and 512 megabytes > > can lead to of memory after running rcuscale with below parameters: > > > > ../kvm.sh --torture rcuscale --allcpus --duration 10 --kconfig CONFIG_NR_CPUS=64 \ > > --bootargs "rcuscale.kfree_rcu_test=1 rcuscale.kfree_nthreads=16 rcuscale.holdoff=20 \ > > rcuscale.kfree_loops=10000 torture.disable_onoff_at_boot" --trust-make > > > > <snip> > > [ 12.054448] kworker/1:1H invoked oom-killer: gfp_mask=0x2cc0(GFP_KERNEL|__GFP_NOWARN), order=0, oom_score_adj=0 > > [ 12.055303] CPU: 1 PID: 377 Comm: kworker/1:1H Not tainted 5.11.0-rc3+ #510 > > [ 12.055416] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.12.0-1 04/01/2014 > > [ 12.056485] Workqueue: events_highpri fill_page_cache_func > > [ 12.056485] Call Trace: > > [ 12.056485] dump_stack+0x57/0x6a > > [ 12.056485] dump_header+0x4c/0x30a > > [ 12.056485] ? del_timer_sync+0x20/0x30 > > [ 12.056485] out_of_memory.cold.47+0xa/0x7e > > [ 12.056485] __alloc_pages_slowpath.constprop.123+0x82f/0xc00 > > [ 12.056485] __alloc_pages_nodemask+0x289/0x2c0 > > [ 12.056485] __get_free_pages+0x8/0x30 > > [ 12.056485] fill_page_cache_func+0x39/0xb0 > > [ 12.056485] process_one_work+0x1ed/0x3b0 > > [ 12.056485] ? process_one_work+0x3b0/0x3b0 > > [ 12.060485] worker_thread+0x28/0x3c0 > > [ 12.060485] ? process_one_work+0x3b0/0x3b0 > > [ 12.060485] kthread+0x138/0x160 > > [ 12.060485] ? kthread_park+0x80/0x80 > > [ 12.060485] ret_from_fork+0x22/0x30 > > [ 12.062156] Mem-Info: > > [ 12.062350] active_anon:0 inactive_anon:0 isolated_anon:0 > > [ 12.062350] active_file:0 inactive_file:0 isolated_file:0 > > [ 12.062350] unevictable:0 dirty:0 writeback:0 > > [ 12.062350] slab_reclaimable:2797 slab_unreclaimable:80920 > > [ 12.062350] mapped:1 shmem:2 pagetables:8 bounce:0 > > [ 12.062350] free:10488 free_pcp:1227 free_cma:0 > > ... > > [ 12.101610] Out of memory and no killable processes... > > [ 12.102042] Kernel panic - not syncing: System is deadlocked on memory > > [ 12.102583] CPU: 1 PID: 377 Comm: kworker/1:1H Not tainted 5.11.0-rc3+ #510 > > [ 12.102600] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.12.0-1 04/01/2014 > > <snip> > > > > Having a fallback mechanism we should not go with "GFP_KERNEL | __GFP_NOWARN" > > that implies a "hard" page request involving OOM killer. Replace such set with > > the same as the one used for a single argument. > > > > Thus it will follow same rules: > > a) minimize a fallback hitting; > > b) avoid of OOM invoking; > > c) do a light-wait page request; > > d) avoid of dipping into the emergency reserves. > > > > With this change an rcuscale and the parameters which are in question > > never runs into "Kernel panic". > > > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx> > > I did have some misgivings about this one, but after a closer look at > the GFP flags you suggest along with offlist discussions it looks like > what needs to happen. So thank you for persisting! ;-) > > I did the usual wordsmithing as shown below, so please check to make > sure that I did not mess anything up. > Looks good to me, i mean a rewording of the commit message :) -- Vlad Rezki
