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[94.245.46.49]) by smtp.gmail.com with ESMTPSA id 24sm1183836ljv.105.2020.04.01.06.23.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Apr 2020 06:23:06 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 1 Apr 2020 15:22:58 +0200 To: Michal Hocko Cc: Uladzislau Rezki , Joel Fernandes , linux-kernel@vger.kernel.org, linux-mm@kvack.org, rcu@vger.kernel.org, willy@infradead.org, peterz@infradead.org, neilb@suse.com, vbabka@suse.cz, mgorman@suse.de, Andrew Morton , Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , "Paul E. McKenney" , Steven Rostedt Subject: Re: [PATCH RFC] rcu/tree: Use GFP_MEMALLOC for alloc memory to free memory pattern Message-ID: <20200401132258.GA1953@pc636> References: <20200331131628.153118-1-joel@joelfernandes.org> <20200331145806.GB236678@google.com> <20200331153450.GM30449@dhcp22.suse.cz> <20200331161215.GA27676@pc636> <20200401070958.GB22681@dhcp22.suse.cz> <20200401123230.GB32593@pc636> <20200401125503.GJ22681@dhcp22.suse.cz> <20200401130816.GA1320@pc636> <20200401131528.GK22681@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200401131528.GK22681@dhcp22.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > We call it from atomic context, so we can not sleep, also we do not have > > any existing context coming from the caller. I see that GFP_ATOMIC is high-level > > flag and is differ from __GFP_ATOMIC. It is defined as: > > > > #define GFP_ATOMIC (__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM) > > > > so basically we would like to have __GFP_KSWAPD_RECLAIM that is included in it, > > because it will also help in case of high memory pressure and wake-up kswapd to > > reclaim memory. > > > > We also can extract: > > > > __GFP_ATOMIC | __GFP_HIGH | __GFP_RETRY_MAYFAIL | __GFP_KSWAPD_RECLAIM > > > > but that is longer then > > > > GFP_ATMOC | __GFP_RETRY_MAYFAIL > > OK, if you are always in the atomic context then GFP_ATOMIC is > sufficient. __GFP_RETRY_MAYFAIL will make no difference for allocations > which do not reclaim (and thus not retry). Sorry this was not clear to > me from the previous description. > Ahh. OK. Then adding __GFP_RETRY_MAYFAIL to GFP_ATOMIC will not make any effect. Thank you for your explanation! -- Vlad Rezki