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AJvYcCWgcCzd9eHjfl/IHVmgT1B1CAmRSDoJAclg9iY424xYtR0LoaStqw5ZI9gYwKINKnlPdSZCawnBaQ==@kvack.org X-Gm-Message-State: AOJu0Yx7Ee6fGgE3DtU0+dHOBmBtPGKUTh2XWluq7UOsEwW5Wkapk+DB 1RbdfE2qJl8zo/KqPlVgmiBDhD35fTTwL9y2hHgQtB37ZYW5fyiyXERnSpnf2dU= X-Google-Smtp-Source: AGHT+IGAG5WENP6E3voq5W3LGdqINSFxDHU4H+x4Vg/h6h2rZ5ugMsP62oKLnr7J1eWj5EzxkxK5vg== X-Received: by 2002:a05:620a:371e:b0:7ab:34c7:10b4 with SMTP id af79cd13be357-7ace744d5e5mr574033185a.47.1727297374549; Wed, 25 Sep 2024 13:49:34 -0700 (PDT) Received: from localhost ([2603:7000:c01:2716:da5e:d3ff:fee7:26e7]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7acde625367sm205555485a.129.2024.09.25.13.49.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Sep 2024 13:49:33 -0700 (PDT) Date: Wed, 25 Sep 2024 16:49:26 -0400 From: Johannes Weiner To: Yosry Ahmed Cc: "Sridhar, Kanchana P" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "nphamcs@gmail.com" , "chengming.zhou@linux.dev" , "usamaarif642@gmail.com" , "shakeel.butt@linux.dev" , "ryan.roberts@arm.com" , "Huang, Ying" , "21cnbao@gmail.com" <21cnbao@gmail.com>, "akpm@linux-foundation.org" , "Zou, Nanhai" , "Feghali, Wajdi K" , "Gopal, Vinodh" Subject: Re: [PATCH v7 6/8] mm: zswap: Support mTHP swapout in zswap_store(). Message-ID: <20240925204926.GB880690@cmpxchg.org> References: <20240924011709.7037-1-kanchana.p.sridhar@intel.com> <20240924011709.7037-7-kanchana.p.sridhar@intel.com> <20240925134008.GA875661@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 18EE216000F X-Stat-Signature: trnjp9qy757bipjgizpctogjn7nb9cab X-Rspam-User: X-HE-Tag: 1727297376-720974 X-HE-Meta: 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 ksxI/vFn 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 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: On Wed, Sep 25, 2024 at 12:49:13PM -0700, Yosry Ahmed wrote: > Kanchana wrote: > > The main question in my mind about using the EWMA checks is, > > will it add overhead to the normal zswap reclaim path; and if so, > > would a simple limit check at the start of zswap_store as suggested > > by Johannes suffice. I can run a few experiments to quantify this > > overhead, and maybe we can revisit this? > > If you look at ewma_##name##_add() in include/linux/average.h, it's > really just a bunch of bit shifts, so I am not concerned about runtime > overhead. My discussion with Johannes is more about if the complexity > is justified, I'd wait for that discussion to settle. Sorry to be blunt, but "precision" in a non-atomic check like this makes no sense. The fact that it's not too expensive is irrelevant. This discussion around this honestly has gone off the rails. Just leave the limit checks exactly as they are. Check limits and cgroup_may_zswap() once up front. Compress the subpages. Acquire references and bump all stats in batches of folio_nr_pages(). You can add up the subpage compressed bytes in the for-loop and do the obj_cgroup_charge_zswap() in a single call at the end as well. That's my suggestion. If that's no good, please ELI5.