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b=ACL1QulaRs5RMSQPqifvediFinODMrrycsn1B0ps7dyoCt0DREDn4tCsH7dFoj8eW Y74QuzpJQBkTS2ZBxS00QEUjvj87p+Gtga0BqTXCWOT5Ey9Lg5oajUYHsRpENsSud9 rzfvHcbH2Yk09ZEHk7Yxy6bN+B7OEqvEzGrFsPLXSHcIFMvddbp3tWrPcGCiBnB0lX t/8u6K812JlHy3fq0JV7D77fPr6Tc2QWF52vfsDzQoUdg43f4yV8W0E0on6UXXm0BA Ec0y14BqRukcJX/KnKwzW0Uuc3SI+6+e7DmVBhsuNyO1ivk3kPspZhJPMsXerofhyT VwOlvu/iZgMsg== Received: by mail-pl1-f177.google.com with SMTP id d9443c01a7336-1d6fbaaec91so6429415ad.3 for ; Wed, 17 Jan 2024 16:18:04 -0800 (PST) X-Gm-Message-State: AOJu0Yyv7wA115wKEHHqQonoq0xQ0YL930+QVP67anKfemcGSVBAJ5LY 58bQoSuOr7wMgb0WJAIbYopHgWQP4Km21JiG8dktHS6QNt6MhsS2rYigYo9a2izRmh2Gm/tY2gH fZ0FqDXCFxlbZhSsZMI3fgFnR1OfDR5vfZvJl X-Google-Smtp-Source: AGHT+IHG7BloajwkgvdQEfRmll3TT9JqCmQbQGfuCAVwO5fLYd194/hQE5j1S0L7XiZ96EoisN5GZbfQtySOzb7NSqs= X-Received: by 2002:a17:902:bb01:b0:1d4:cd41:e44b with SMTP id im1-20020a170902bb0100b001d4cd41e44bmr84916plb.124.1705537083735; Wed, 17 Jan 2024 16:18:03 -0800 (PST) MIME-Version: 1.0 References: <20240117-b4-zswap-lock-optimize-v1-0-23f6effe5775@bytedance.com> In-Reply-To: From: Chris Li Date: Wed, 17 Jan 2024 16:17:51 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 0/2] mm/zswap: optimize the scalability of zswap rb-tree To: Yosry Ahmed Cc: Chengming Zhou , Andrew Morton , linux-kernel@vger.kernel.org, Johannes Weiner , linux-mm@kvack.org, Nhat Pham Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 175B9100012 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: o8mt16hpzyjiy9tbt7rzk8mnp9fz5u4b X-HE-Tag: 1705537088-844579 X-HE-Meta: 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 jvKkKv+s R2Kg6hZXqq89sO/lV9hIu//P8nBxRJX9M4SK8h5buXYU1EaYKbDgdpwOSBsM5/7SlhY2KTreupbBWyBGluoXqhDx17G92qimL2jxfLLgQ5cOyryuoPJY/cZ1yqST1Gd8MoyGdkZ10Haomp2YRQjr/PM/7a83E6TLp7kqGXj5yGjZUfzM4w5n04i8qP87h4zpujGwod8/dii14cmCfq1/EyaY8zlNeEqsvi73cArFoZWq2vok= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Yosry, On Wed, Jan 17, 2024 at 3:48=E2=80=AFPM Yosry Ahmed = wrote: > > > Currently the xarray patch should have everything it takes to use RCU > > read lock. However taking out the tree spinlock is more work than > > previously. If we are going to remove the tree spinlock, I think we > > should revert back to doing a zswap tree lookup and return the zswap > > entry with reference increased. The tree mapping can still decouple > > from the zswap entry reference count drop to zero. Anyway, my V1 of > > the xarray patch will not include removing the tree spinlock. > > Interesting. What do you mean by removing the tree spinlock? My > assumption was that the xarray reduces lock contention because we do > not need a lock to do lookups, but we still need the lock otherwise. > Did you have something in mind to completely remove the tree lock? In my current xarray series, it adds the xarray alongside the rb tree. Xarray has its own internal lock as well. Effectively zswap now has two locks instead of just one previously. The xarray lock will not have any contention due to the xarray lock taken inside the zswap rb tree lock. The eventual goal is reducing the two locks back to one(xarray lock), which is not in my V1 patch. Your understanding is correct, the xarray still needs to have one lock for protecting the write path. > > > The reason why I think we should wait for the xarray patch(es) is > > > there is a chance we may see less improvements from splitting the tre= e > > > if it was an xarray. If we merge this series first, there is no way t= o > > > know. > > > > > > Chris, do you intend to send the xarray patch(es) anytime soon? > > > > Thanks for the heads up. Let me send it out now. > > Awesome, thanks! I assume Chengming can test whether this series > provides the same benefits with the xarray. That would be great. The xarray patch needs more testing for sure. Chris