From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH RFC v2 02/10] mm: Make shrink_slab() lockless To: Tetsuo Handa Cc: Michal Hocko , akpm@linux-foundation.org, gregkh@linuxfoundation.org, rafael@kernel.org, viro@zeniv.linux.org.uk, darrick.wong@oracle.com, paulmck@linux.vnet.ibm.com, josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, hughd@google.com, shuah@kernel.org, robh@kernel.org, ulf.hansson@linaro.org, aspriel@gmail.com, vivek.gautam@codeaurora.org, robin.murphy@arm.com, joe@perches.com, heikki.krogerus@linux.intel.com, sfr@canb.auug.org.au, vdavydov.dev@gmail.com, chris@chris-wilson.co.uk, aryabinin@virtuozzo.com, willy@infradead.org, ying.huang@intel.com, shakeelb@google.com, jbacik@fb.com, mingo@kernel.org, mhiramat@kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org References: <153365347929.19074.12509495712735843805.stgit@localhost.localdomain> <153365626605.19074.16202958374930777592.stgit@localhost.localdomain> <591d2063-0511-103d-bef6-dd35f55afe32@virtuozzo.com> <4ceb948c-7ce7-0db3-17d8-82ef1e6e47cc@virtuozzo.com> <20180809071418.GA24884@dhcp22.suse.cz> <7b746367-e4bc-0e64-4e27-14fd7f06ba8f@i-love.sakura.ne.jp> From: Kirill Tkhai Message-ID: <2e1cdec3-5133-67ec-e929-8bc174574b3a@virtuozzo.com> Date: Thu, 9 Aug 2018 13:58:16 +0300 MIME-Version: 1.0 In-Reply-To: <7b746367-e4bc-0e64-4e27-14fd7f06ba8f@i-love.sakura.ne.jp> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: On 09.08.2018 13:37, Tetsuo Handa wrote: > On 2018/08/09 18:21, Kirill Tkhai wrote: >> 2)SRCU. Pros are there are no the above problems; we will have completely unlocked and >> scalable shrink_slab(). We will also have a possibility to avoid unregistering delays, >> like I did for superblock shrinker. There will be full scalability. >> Cons is enabling SRCU. >> > > How unregistering delays can be avoided? Since you traverse all shrinkers > using one shrinker_srcu, synchronize_srcu(&shrinker_srcu) will block > unregistering threads until longest inflight srcu_read_lock() user calls > srcu_read_unlock(). Yes, but we can do synchronize_srcu() from async work like I did for the further patches. The only thing we need is to teach shrinker::count_objects() and shrinker::scan_objects() be safe to be called on unregistering shrinker user. The next patches do this for superblock shrinker. > Unless you use per shrinker counter like below, I wonder whether > unregistering delays can be avoided... > > https://marc.info/?l=linux-mm&m=151060909613004 > https://marc.info/?l=linux-mm&m=151060909713005 I'm afraid these atomic_{inc,dec}(&shrinker->nr_active) may regulary drop CPU caches on another CPUs on some workloads. Also, synchronize_rcu() is also a heavy delay.