The following commit has been merged into the core/rcu branch of tip:
Commit-ID: 3e7ce7a187fc6aaa9fda1310a2b8da8770342ff7
Gitweb:
https://git.kernel.org/tip/3e7ce7a187fc6aaa9fda1310a2b8da8770342ff7
Author: Uladzislau Rezki (Sony) <ure...@gmail.com>
AuthorDate: Fri, 29 Jan 2021 17:16:03 +01:00
Committer: Paul E. McKenney <paul...@kernel.org>
CommitterDate: Mon, 08 Mar 2021 14:18:07 -08:00
kvfree_rcu: Replace __GFP_RETRY_MAYFAIL by __GFP_NORETRY
__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) <ure...@gmail.com>
Acked-by: Michal Hocko <mho...@suse.com>
Signed-off-by: Paul E. McKenney <paul...@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);
}
