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[86.146.209.214]) by smtp.gmail.com with ESMTPSA id s17-20020a5d4251000000b002d1801018e2sm10633773wrr.63.2023.03.21.00.48.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Mar 2023 00:48:29 -0700 (PDT) Date: Tue, 21 Mar 2023 07:48:29 +0000 From: Lorenzo Stoakes To: Uladzislau Rezki Cc: lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org Subject: Re: LSFMMBPF proposal [MM]: Eliminate vmap/vmalloc lock contention Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: 69660140015 X-Rspamd-Server: rspam01 X-Stat-Signature: 3sdz6bkctmfz1kgpojnfru31hwnb3s9u X-HE-Tag: 1679384912-36682 X-HE-Meta: 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 MHzShD8V WzVrAsHF6awwnXXLQkPmK3GX0ANck88Ntxv0D7B4F/Yv+3vHz+uAiKOgaf82eraU0Bb4u+PBON3g3qw1O1Cm2f5WsrC1tnitY2EIfiBTBcpdRaQFQNHL2LCqYFMQmX1hDSWCJu+iJ4RD2rPZUaEcDas6N3HD5c5+04Xgw1gI6P6YAd68XPRBwGBdZYXYQDbnbaczzVKUlo+nVjYM6o9ychtpSOaoOVp6vgu4YyzujXaUAS7eok30jbnDtMFOe3ckfohmYdmfj8YbjBLbx8+RoebwmHjm5SVQS17uDdc6E5d5Ek5VeuDHkFfAz0KhzlJVvPGK6enARRmwB7YZsNMB6UD4IfvVI3Gw5z9MXSXxL7ooBnFgY81zUsQf+6ZAoLvYPVxJtYMNAcliECbGy3nZE33CfsQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000268, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Feb 28, 2023 at 05:42:43PM +0100, Uladzislau Rezki wrote: > Hello, LSF. > > Title: Introduce a per-cpu-vmap-cache to eliminate a vmap lock contention > > Description: > Currently the vmap code is not scaled to number of CPU cores in a system > because a global vmap space is protected by a single spinlock. Such approach > has a clear bottleneck if many CPUs simultaneously access to one resource. > > In this talk i would like to describe a drawback, show some data related > to contentions and places where those occur in a code. Apart of that i > would like to share ideas how to eliminate it providing a few approaches > and compare them. > > Requirements: > * It should be a per-cpu approach; > * Search of freed ptrs should not interfere with other freeing(as much as we can); > * - offload allocated areas(buzy ones) per-cpu; > * Cache ready sized objects or merge them into one big per-cpu-space(split on demand); > * Lazily-freed areas either drained per-cpu individually or by one CPU for all; > * Prefetch a fixed size in front and allocate per-cpu > > Goals: > * Implement a per-cpu way of allocation to eliminate a contention. > > Thanks! > > -- > Uladzislau Rezki > This is a really interesting topic and I'd really like this to go ahead as there's certainly been a lot of discussion regarding vmalloc locking of late. I for one would certainly attend it.