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[37.188.180.223]) by smtp.gmail.com with ESMTPSA id a8sm3136708wmb.39.2020.04.09.03.34.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Apr 2020 03:34:02 -0700 (PDT) Date: Thu, 9 Apr 2020 12:34:00 +0200 From: Michal Hocko To: Bruno =?iso-8859-1?Q?Pr=E9mont?= Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, Johannes Weiner , Vladimir Davydov , Chris Down Subject: Re: Memory CG and 5.1 to 5.6 uprade slows backup Message-ID: <20200409103400.GF18386@dhcp22.suse.cz> References: <20200409112505.2e1fc150@hemera.lan.sysophe.eu> <20200409094615.GE18386@dhcp22.suse.cz> <20200409121733.1a5ba17c@hemera.lan.sysophe.eu> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20200409121733.1a5ba17c@hemera.lan.sysophe.eu> Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.001193, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu 09-04-20 12:17:33, Bruno Pr=E9mont wrote: > On Thu, 9 Apr 2020 11:46:15 Michal Hocko wrote: > > [Cc Chris] > >=20 > > On Thu 09-04-20 11:25:05, Bruno Pr=E9mont wrote: > > > Hi, > > >=20 > > > Upgrading from 5.1 kernel to 5.6 kernel on a production system usin= g > > > cgroups (v2) and having backup process in a memory.high=3D2G cgroup > > > sees backup being highly throttled (there are about 1.5T to be > > > backuped). =20 > >=20 > > What does /proc/sys/vm/dirty_* say? >=20 > /proc/sys/vm/dirty_background_bytes:0 > /proc/sys/vm/dirty_background_ratio:10 > /proc/sys/vm/dirty_bytes:0 > /proc/sys/vm/dirty_expire_centisecs:3000 > /proc/sys/vm/dirty_ratio:20 > /proc/sys/vm/dirty_writeback_centisecs:500 Sorry, but I forgot ask for the total amount of memory. But it seems this is 64GB and 10% dirty ration might mean a lot of dirty memory. Does the same happen if you reduce those knobs to something smaller than 2G? _bytes alternatives should be useful for that purpose. [...] > > Is it possible that the reclaim is not making progress on too many > > dirty pages and that triggers the back off mechanism that has been > > implemented recently in 5.4 (have a look at 0e4b01df8659 ("mm, > > memcg: throttle allocators when failing reclaim over memory.high") > > and e26733e0d0ec ("mm, memcg: throttle allocators based on > > ancestral memory.high"). >=20 > Could be though in that case it's throttling the wrong task/cgroup > as far as I can see (at least from cgroup's memory stats) or being > blocked by state external to the cgroup. > Will have a look at those patches so get a better idea at what they > change. Could you check where is the task of your interest throttled? /proc//stack should give you a clue. --=20 Michal Hocko SUSE Labs