Messages in this thread Patch in this message | | | From | paulmck@kernel ... | 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 |
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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
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