From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
"Uladzislau Rezki (Sony)" <urezki@gmail.com>,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 4/6] kvfree_rcu: Replace __GFP_RETRY_MAYFAIL by __GFP_NORETRY
Date: Wed, 3 Mar 2021 16:11:32 -0800 [thread overview]
Message-ID: <20210304001134.22977-4-paulmck@kernel.org> (raw)
In-Reply-To: <20210304001044.GA22871@paulmck-ThinkPad-P72>
From: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
__GFP_RETRY_MAYFAIL can spend quite a bit of time reclaiming, and this
can be wasted effort given that there is a fallback code path in case
memory allocation fails.
__GFP_NORETRY does perform some light-weight reclaim, but it will fail
under OOM conditions, allowing the fallback to be taken as an alternative
to hard-OOMing the system.
There is a four-way tradeoff that must be balanced:
1) Minimize use of the fallback path;
2) Avoid full-up OOM;
3) Do a light-wait allocation request;
4) Avoid dipping into the emergency reserves.
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 7ee83f3..0ecc1fb 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3517,8 +3517,20 @@ add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
bnode = get_cached_bnode(*krcp);
if (!bnode && can_alloc) {
krc_this_cpu_unlock(*krcp, *flags);
+
+ // __GFP_NORETRY - allows a light-weight direct reclaim
+ // what is OK from minimizing of fallback hitting point of
+ // view. Apart of that it forbids any OOM invoking what is
+ // also beneficial since we are about to release memory soon.
+ //
+ // __GFP_NOMEMALLOC - prevents from consuming of all the
+ // memory reserves. Please note we have a fallback path.
+ //
+ // __GFP_NOWARN - it is supposed that an allocation can
+ // be failed under low memory or high memory pressure
+ // scenarios.
bnode = (struct kvfree_rcu_bulk_data *)
- __get_free_page(GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOMEMALLOC | __GFP_NOWARN);
+ __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
*krcp = krc_this_cpu_lock(flags);
}
--
2.9.5
next prev parent reply other threads:[~2021-03-04 0:18 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-04 0:10 [PATCH tip/core/rcu 0/6] kvfree_rcu() updates for v5.12-rc1 Paul E. McKenney
2021-03-04 0:11 ` [PATCH tip/core/rcu 1/6] kvfree_rcu: Directly allocate page for single-argument case paulmck
2021-03-04 0:11 ` [PATCH tip/core/rcu 2/6] kvfree_rcu: Use __GFP_NOMEMALLOC for single-argument kvfree_rcu() paulmck
2021-03-04 0:11 ` [PATCH tip/core/rcu 3/6] kvfree_rcu: Make krc_this_cpu_unlock() use raw_spin_unlock_irqrestore() paulmck
2021-03-04 0:11 ` paulmck [this message]
2021-03-04 0:11 ` [PATCH tip/core/rcu 5/6] kvfree_rcu: Use same set of GFP flags as does single-argument paulmck
2021-03-04 0:11 ` [PATCH tip/core/rcu 6/6] rcuscale: Add kfree_rcu() single-argument scale test paulmck
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