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bh=TCcPBABBzltDpyoJKRY9SuJLYXgsWgL74mEX6T6kSR8=; b=TIXLNoECbYLOwtS1hjRZUvuUJ0tZMIx/cuKDHSYn9xScVxBqdlTSxLM1H1X5jzmJ/or2k/ gARXZRoHZR3271hDg/r9XBvpqghfooiJwmluXmQf+sJ9IhOK7PkCW4fxUfv0bek0KNhbpX LMPrg5MDruGN69SQP+JMNeERZr+LaFY= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 9161A139D2; Wed, 18 Jan 2023 09:49:30 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id DyT3IqrAx2OtQgAAMHmgww (envelope-from ); Wed, 18 Jan 2023 09:49:30 +0000 Date: Wed, 18 Jan 2023 10:49:26 +0100 From: Michal Hocko To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, michel@lespinasse.org, jglisse@google.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com, paulmck@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, jannh@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, hughlynch@google.com, leewalsh@google.com, posk@google.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH 39/41] kernel/fork: throttle call_rcu() calls in vm_area_free Message-ID: References: <20230109205336.3665937-1-surenb@google.com> <20230109205336.3665937-40-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: C6712100016 X-Stat-Signature: i343dxfu9s75dr3yisw4ai6zwxpr855n X-Rspam-User: X-HE-Tag: 1674035373-186811 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000044, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue 17-01-23 17:19:46, Suren Baghdasaryan wrote: > On Tue, Jan 17, 2023 at 7:57 AM Michal Hocko wrote: > > > > On Mon 09-01-23 12:53:34, Suren Baghdasaryan wrote: > > > call_rcu() can take a long time when callback offloading is enabled. > > > Its use in the vm_area_free can cause regressions in the exit path when > > > multiple VMAs are being freed. > > > > What kind of regressions. > > > > > To minimize that impact, place VMAs into > > > a list and free them in groups using one call_rcu() call per group. > > > > Please add some data to justify this additional complexity. > > Sorry, should have done that in the first place. A 4.3% regression was > noticed when running execl test from unixbench suite. spawn test also > showed 1.6% regression. Profiling revealed that vma freeing was taking > longer due to call_rcu() which is slow when RCU callback offloading is > enabled. Could you be more specific? vma freeing is async with the RCU so how come this has resulted in a regression? Is there any heavy rcu_synchronize in the exec path? That would be an interesting information. -- Michal Hocko SUSE Labs