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AJvYcCUKK7fRi73AmGNIdNX2fGPgzQAghC075CnrW17NQ9n98LMUmFAnbc4F+8na6H8CnGbI+XufegnhPkuhQVgZA1KGAos= X-Gm-Message-State: AOJu0YzNRDbiEtTJK0tanBCcezW/rqc/0fd+tZg2ljmr/rqqVn9mn3L/ oQe0swFgtZtWuPF4At9+P2WvqFX7dfa8BgS/6pkS6vS5bGJskI2ACoIwKLXm5oQqP72wCWWWzVY M5J98r96N0+kDtPhf8ZfpZUDQrgc= X-Google-Smtp-Source: AGHT+IEbntKw0TZ+iqky2+3ROVE92PMozct8oAp70ngs5dFm+54BCSXy7L+xhXtRVUDDoWuOYT9ck2VsNIbmJgypQYY= X-Received: by 2002:a25:d38c:0:b0:dfa:599e:8b74 with SMTP id 3f1490d57ef6-dfaf659531fmr1169315276.10.1717722053424; Thu, 06 Jun 2024 18:00:53 -0700 (PDT) MIME-Version: 1.0 References: <20240606165303.431215-1-flintglass@gmail.com> In-Reply-To: From: Takero Funaki Date: Fri, 7 Jun 2024 10:00:43 +0900 Message-ID: Subject: Re: [PATCH] mm: zswap: limit number of zpools based on CPU and RAM To: Yosry Ahmed Cc: Johannes Weiner , Nhat Pham , Chengming Zhou , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 6D51B40003 X-Rspam-User: X-Rspamd-Server: rspam12 X-Stat-Signature: z7hdzohhatkepsfhecjqny6xg4att7ci X-HE-Tag: 1717722054-223604 X-HE-Meta: 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 P+e/pY2N RdhXD5sXe1Y3AFNEB5QaCncc2bXewhs9yNfvqpgUtyOnWbI+0cHqcAT8InvXWrgCJWK9v1o6Wa11KVORC5G5EbKYLhnq0ycuBROQd7sUCwfVpq7eRmNJBHihXnrTc+xnp42MeCgkKdXAt6iCEYsjM9mb+0mTGpxP0gGuIXSgfxx77TdwHeBOJa2e8BKVdJXv4OOJarxV6rcI8dmZcY7xYdQv3DoHTIPcGJYLAtDyINGCENmKhhzZLPRVbXAwiWZguq/zxHTlWbM6f4qNSWOOfNEOHEYefuZTS0QXSbmiIW3OYCz4PhHkc8sgdRWpbUrwz4gRzbXMIreYIJTc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000879, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 2024=E5=B9=B46=E6=9C=887=E6=97=A5(=E9=87=91) 2:46 Yosry Ahmed : > > There are a lot of magic numbers in this patch, and it seems like it's > all based on theory. I don't object to making the number of zpools > dynamic in some way, but unless we do it in a data-driven way where we > understand the implications, I think the added complexity and > inconsistency is not justified. > > For example, 2*CPU zpools is an overkill and will cause a lot of > fragmentation. We use 32 zpools right now for machines with 100s of > CPUs. I know that you are keeping 32 as the limit, but why 2*CPUs if > nr_cpus <=3D 16? > > Also, the limitation based on memory size assumes that zsmalloc is the > only allocator used by zswap, which is unfortunately not the case. > > The current implementation using 32 zpools all the time is not > perfect, and I did write a patch to make it at least be min(nr_cpus, > 32), but it is simple and it works. Complexity should be justified. > Thanks for your comments. I agree the 2*cpu is too much. it was conservatively chosen assuming 1/2 contention while all cores are accessing zswap. Much smaller factor or non-linear scale as your comments in the main thread would be better. I found your patch from the main thread. One point I'm afraid, this hashing will fail if nr_zswap_zpools is 1 or is not rounded to order of 2. hash_ptr crashes when bit is 0. > + return entry->pool->zpools[hash_ptr(entry, ilog2(nr_zswap_zpools))];