Re: [PATCH 1/3] kvfree_rcu: Allocate a page for a single argument

From: Michal Hocko
Date: Mon Jan 25 2021 - 08:30:06 EST


On Wed 20-01-21 17:21:46, Uladzislau Rezki (Sony) wrote:
> For a single argument we can directly request a page from a caller
> context when a "carry page block" is run out of free spots. Instead
> of hitting a slow path we can request an extra page by demand and
> proceed with a fast path.
>
> A single-argument kvfree_rcu() must be invoked in sleepable contexts,
> and that its fallback is the relatively high latency synchronize_rcu().
> Single-argument kvfree_rcu() therefore uses GFP_KERNEL|__GFP_RETRY_MAYFAIL
> to allow limited sleeping within the memory allocator.

__GFP_RETRY_MAYFAIL can be quite heavy. It is effectively the most heavy
way to allocate without triggering the OOM killer. Is this really what
you need/want? Is __GFP_NORETRY too weak?

--
Michal Hocko
SUSE Labs