From 540718a4d19e40a0aab19cd06237eed6413753b5 Mon Sep 17 00:00:00 2001 From: "Uladzislau Rezki (Sony)" Date: Fri, 29 Jan 2021 21:05:05 +0100 Subject: [PATCH] kvfree_rcu: Use same set of GFP flags as does single-argument 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 result in OOM when 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 [ 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 Because kvfree_rcu() has a fallback path, memory allocation failure is not the end of the world. Furthermore, the added overhead of aggressive GFP settings must be balanced against the overhead of the fallback path, which is a cache miss for double-argument kvfree_rcu() and a call to synchronize_rcu() for single-argument kvfree_rcu(). The current choice of GFP_KERNEL|__GFP_NOWARN can result in longer latencies than a call to synchronize_rcu(), so less-tenacious GFP flags would be helpful. Here is the tradeoff that must be balanced: a) Minimize use of the fallback path, b) Avoid pushing the system into OOM, c) Bound allocation latency to that of synchronize_rcu(), and d) Leave the emergency reserves to use cases lacking fallbacks. This commit therefore changes GFP flags from GFP_KERNEL|__GFP_NOWARN to GFP_KERNEL|__GFP_NORETRY|__GFP_NOMEMALLOC|__GFP_NOWARN. This combination leaves the emergency reserves alone and can initiate reclaim, but will not invoke the OOM killer. Signed-off-by: Uladzislau Rezki (Sony) Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 0571d484d79490..47e762e51ad0e7 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3411,7 +3411,7 @@ static void fill_page_cache_func(struct work_struct *work) for (i = 0; i < rcu_min_cached_objs; i++) { bnode = (struct kvfree_rcu_bulk_data *) - __get_free_page(GFP_KERNEL | __GFP_NOWARN); + __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN); if (bnode) { raw_spin_lock_irqsave(&krcp->lock, flags);