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[2603:7000:c01:2716:da5e:d3ff:fee7:26e7]) by smtp.gmail.com with ESMTPSA id q13-20020ad4574d000000b00692bd4905c9sm4943884qvx.15.2024.03.20.02.50.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 Mar 2024 02:51:00 -0700 (PDT) Date: Wed, 20 Mar 2024 05:50:53 -0400 From: Johannes Weiner To: Yosry Ahmed Cc: Andrew Morton , Nhat Pham , Chengming Zhou , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm: zswap: increase shrinking protection for zswap swapins only Message-ID: <20240320095053.GA294822@cmpxchg.org> References: <20240320020823.337644-1-yosryahmed@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240320020823.337644-1-yosryahmed@google.com> X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 96ED940003 X-Stat-Signature: aseofxc6qesoxitaqth389riega8xx9n X-Rspam-User: X-HE-Tag: 1710928261-726760 X-HE-Meta: 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 W8i8qZpR xnKuPZ9WbWl3Z3ilWJM8DMsZo87rY/wv/0QPdn6pUPwSPtvXeTfGQb0WvkDv4eREexAK0D1nxdEd9upp5VOKkwR9siJ3DCXhIlZcTqZjddEFDXb63ci1B0p+u7K2aTtnlVBmSOXxiM5ozqwr1MT8lIIp2Wtl9WG+aP7X9EtluasSDcsv3JLcYhGW2BkAvblQ8Jzmg/iwt46/F9eMLFpPYXK0YhmBnHh3aPtxKUb+WMuzkaSePpS0HvZrLaR7RLUY+Pb4zuaun0PKya/wREdI/oa9u71nd+duDr6Vpe5o4G+bFXW9JnhrHaiwdP/BzzFxrSOi/j57tYlxn/VN1LHbiKPPEVCvnfSDLH9q+oXveuqm83jWEIEcw+Jt14swS8DBorPNeQLqSA6mIDpw= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000083, 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, Mar 20, 2024 at 02:08:22AM +0000, Yosry Ahmed wrote: > Currently, the number of protected zswap entries corresponding to an > lruvec are incremented every time we swapin a page. Correct. This is the primary signal that the shrinker is being too aggressive in moving entries to disk and should slow down...? > This happens regardless of whether or not the page originated in > zswap. Hence, swapins from disk will lead to increasing protection > on potentially stale zswap entries. Furthermore, the increased > shrinking protection can lead to more pages skipping zswap and going > to disk, eventually leading to even more swapins from disk and > starting a vicious circle. How does shrinker protection affect zswap stores? On the contrary, I would expect this patch to create a runaway shrinker. The more aggressively it moves entries out to disk, the lower the rate of zswap loads, the more aggressively it moves more entries out to disk. > Instead, only increase the protection when pages are loaded from zswap. > This also has a nice side effect of removing zswap_folio_swapin() and > replacing it with a static helper that is only called from zswap_load(). > > No problems were observed in practice, this was found through code > inspection. This is missing test results :)