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Wed, 06 Dec 2023 19:25:19 -0800 (PST) Received: from [10.255.200.168] ([139.177.225.241]) by smtp.gmail.com with ESMTPSA id a2-20020a62d402000000b006ce95e37a40sm261930pfh.111.2023.12.06.19.25.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 06 Dec 2023 19:25:19 -0800 (PST) Message-ID: <77d628dc-ab8c-4d8c-bc63-7e4518ea92d7@bytedance.com> Date: Thu, 7 Dec 2023 11:25:13 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/7] mm/zswap: optimize the scalability of zswap rb-tree Content-Language: en-US To: Chris Li , Yosry Ahmed , Nhat Pham Cc: Vitaly Wool , Johannes Weiner , Michal Hocko , Seth Jennings , Dan Streetman , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Matthew Wilcox References: <20231206-zswap-lock-optimize-v1-0-e25b059f9c3a@bytedance.com> From: Chengming Zhou In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 043611C001B X-Rspam-User: X-Stat-Signature: xa48koe9nq758qmscrcm3thb7fmnbq5d X-Rspamd-Server: rspam03 X-HE-Tag: 1701919520-142360 X-HE-Meta: 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 oLHMPqty M4zt0jktZsMGD8SaNJ+uMGfgc5TpZgNTg+PXOgDNff4FFVfbh/KhEjvE+Atu7EPLjRfmfzbDffnQtqjbfUNHwp9TAX3bopLRz1UikCCzsxkASwUFLr4EBh7TkGO9IYowaEUUPlCycHmt2LxdSgJzOl8BPCGpL31FQuWXG+/D0NHdrx225zY+yrIVuXV78wB1kgBtKjYfGANmUlJbIf2DOvatckBtbzziOKTnAe6CQ++lgsY+Z322IYI4QBMJgvP8Dn1RmzdSOFaw7RGZLra7SnqUlArF0sxKJEsnAg5g6DSnbmO6ouh186xZh4+Pp1pE3qDW/xT3x5B5l27MFbTtgAE9BDjEgaaZmQ6P3gYOOyG2YpuAZ+yqaIZnl9HrZjn0wKjdc4Mqi+AcHHJyA2zpS/4F/YzPcwJQn9kmC3f6qLU8+kMXDP5tcBQUl/rlZ0oDyDuLl4c1AJa7MZ9c= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000003, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2023/12/7 08:43, Chris Li wrote: > Hi Nhat and Yosry, > > On Wed, Dec 6, 2023 at 12:42 PM Yosry Ahmed wrote: >> >> On Wed, Dec 6, 2023 at 9:24 AM Nhat Pham wrote: >>> >>> + Chris Li >>> >>> Chris, I vaguely remember from our last conversation that you have >>> some concurrent efforts to use xarray here right? > > Yes, I do have the zswap xarray for older versions of the kernel. The > recent mm-unstable tree has a lot of zswap related updates. Give me 2 > days to refresh and post it. The zswap invalid entry and the reference > count change is causing a good portion of the code to be updated. That > is the price to pay keeping out of tree patches. My fault is not > getting to it sooner. > >> >> If I recall correctly, the xarray already reduces the lock contention >> as lookups are lockless, but Chris knows more here. As you mentioned > > Yes. To be exact, xarray can use spin lock (same as current RB tree) > or take RCU read lock on the lookup path (depending on how you call > the xarray API). Not completely lockless but the RCU read lock should > have less lock contention than normal spinlock. +Matthew > Great! Lockless lookup in zswap_load() should reduce spinlock contention. And multiple trees (multiple xarrays) can further reduce the contention on the concurrent zswap_store() side. So it's complementary IMHO. >> in a different email, it would be nice to get some data so that we can >> compare different solutions. > > Yes, it is certainly welcome to see more data points. If I recall > correctly, the zswap xarray array makes the lookup similar to the swap > cache lookup. It has a noticeable difference in the long tail end. > Right, I post some data from yesterday in another reply. Will test again and update the data since Nhat's zswap shrinker fix patch has been merged into mm-unstable today. Thanks!