On Mon, Feb 01, 2021 at 12:47:55PM +0100, Michal Hocko wrote: > On Fri 29-01-21 17:35:31, Uladzislau Rezki wrote: > > 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(): > > > > >From ec2feaa9b7f55f73b3b17e9ac372151c1aab5ae0 Mon Sep 17 00:00:00 2001 > > From: "Uladzislau Rezki (Sony)" <urezki@xxxxxxxxx> > > Date: Fri, 29 Jan 2021 17:16:03 +0100 > > Subject: [PATCH 1/1] kvfree_rcu: replace __GFP_RETRY_MAYFAIL by __GFP_NORETRY > > > > __GFP_RETRY_MAYFAIL is a bit heavy from reclaim process of view, > > therefore a time consuming. That is not optional and there is > > no need in doing it so hard, because we have a fallback path. > > > > __GFP_NORETRY in its turn can perform some light-weight reclaim > > and it rather fails under high memory pressure or low memory > > condition. > > > > In general there are four simple criterias we we would like to > > achieve: > > a) minimize a fallback hitting; > > b) avoid of OOM invoking; > > c) do a light-wait page request; > > d) avoid of dipping into the emergency reserves. > > > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx> > > Looks good to me. Feel free to add > Acked-by: Michal Hocko <mhocko@xxxxxxxx> > Appreciate it! -- Vlad Rezki
