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

[Uladzislau Rezki]

On Fri, Jan 29, 2021 at 09:56:29AM +0100, Michal Hocko wrote:
> On Thu 28-01-21 19:02:37, Uladzislau Rezki wrote:
> [...]
> > >From 0bdb8ca1ae62088790e0a452c4acec3821e06989 Mon Sep 17 00:00:00 2001
> > From: "Uladzislau Rezki (Sony)" <urezki@xxxxxxxxx>
> > Date: Wed, 20 Jan 2021 17:21:46 +0100
> > Subject: [PATCH v2 1/1] kvfree_rcu: Directly allocate page for single-argument
> >  case
> > 
> > Single-argument kvfree_rcu() must be invoked from sleepable contexts,
> > so we can directly allocate pages.  Furthermmore, the fallback in case
> > of page-allocation failure is the high-latency synchronize_rcu(), so it
> > makes sense to do these page allocations from the fastpath, and even to
> > permit limited sleeping within the allocator.
> > 
> > This commit therefore allocates if needed on the fastpath using
> > GFP_KERNEL|__GFP_NORETRY.
> 
> Yes, __GFP_NORETRY as a lightweight allocation mode should be fine. It
> is more robust than __GFP_NOWAIT on memory usage spikes.  The caller is
> prepared to handle the failure which is likely much less disruptive than
> OOM or potentially heavy reclaim __GFP_RETRY_MAYFAIL.
> 
> I cannot give you ack as I am not familiar with the code but this makes
> sense to me.
> 
No problem, i can separate it. We can have a patch on top of what we have so
far. The patch only modifies the gfp_mask passed to __get_free_pages():