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Tue, 08 Apr 2025 06:04:09 -0700 (PDT) Received: from [172.17.139.17] ([163.114.131.192]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ac7bfe99c7dsm919058366b.57.2025.04.08.06.04.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Apr 2025 06:04:08 -0700 (PDT) Message-ID: <983965b6-2262-4f72-a672-39085dcdaa3c@gmail.com> Date: Tue, 8 Apr 2025 14:04:06 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 00/14] Virtual Swap Space To: Nhat Pham , linux-mm@kvack.org Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, hughd@google.com, yosry.ahmed@linux.dev, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, len.brown@intel.com, chengming.zhou@linux.dev, kasong@tencent.com, chrisl@kernel.org, huang.ying.caritas@gmail.com, ryan.roberts@arm.com, viro@zeniv.linux.org.uk, baohua@kernel.org, osalvador@suse.de, lorenzo.stoakes@oracle.com, christophe.leroy@csgroup.eu, pavel@kernel.org, kernel-team@meta.com, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-pm@vger.kernel.org References: <20250407234223.1059191-1-nphamcs@gmail.com> Content-Language: en-US From: Usama Arif In-Reply-To: <20250407234223.1059191-1-nphamcs@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 08/04/2025 00:42, Nhat Pham wrote: > > V. Benchmarking > > As a proof of concept, I run the prototype through some simple > benchmarks: > > 1. usemem: 16 threads, 2G each, memory.max = 16G > > I benchmarked the following usemem commands: > > time usemem --init-time -w -O -s 10 -n 16 2g > > Baseline: > real: 33.96s > user: 25.31s > sys: 341.09s > average throughput: 111295.45 KB/s > average free time: 2079258.68 usecs > > New Design: > real: 35.87s > user: 25.15s > sys: 373.01s > average throughput: 106965.46 KB/s > average free time: 3192465.62 usecs > > To root cause this regression, I ran perf on the usemem program, as > well as on the following stress-ng program: > > perf record -ag -e cycles -G perf_cg -- ./stress-ng/stress-ng --pageswap $(nproc) --pageswap-ops 100000 > > and observed the (predicted) increase in lock contention on swap cache > accesses. This regression is alleviated if I put together the > following hack: limit the virtual swap space to a sufficient size for > the benchmark, range partition the swap-related data structures (swap > cache, zswap tree, etc.) based on the limit, and distribute the > allocation of virtual swap slotss among these partitions (on a per-CPU > basis): > > real: 34.94s > user: 25.28s > sys: 360.25s > average throughput: 108181.15 KB/s > average free time: 2680890.24 usecs > > As mentioned above, I will implement proper dynamic swap range > partitioning in a follow up work. > > 2. Kernel building: zswap enabled, 52 workers (one per processor), > memory.max = 3G. > > Baseline: > real: 183.55s > user: 5119.01s > sys: 655.16s > > New Design: > real: mean: 184.5s > user: mean: 5117.4s > sys: mean: 695.23s > > New Design (Static Partition) > real: 183.95s > user: 5119.29s > sys: 664.24s > Hi Nhat, Thanks for the patches! I have glanced over a couple of them, but this was the main question that came to my mind. Just wanted to check if you had a look at the memory regression during these benchmarks? Also what is sizeof(swp_desc)? Maybe we can calculate the memory overhead as sizeof(swp_desc) * swap size/PAGE_SIZE? For a 64G swap that is filled with private anon pages, the overhead in MB might be (sizeof(swp_desc) in bytes * 16M) - 16M (zerobitmap) - 16M*8 (swap map)? This looks like a sizeable memory regression? Thanks, Usama