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AJvYcCWwAk40OB8K093fAokTcQmwjeoJVOba9tWq1HHvr5aDTAc4R9/MC3NvKO4pVTpZmMfX0y0FrIHrggzbFROVK3Q7IWU= X-Gm-Message-State: AOJu0YwVs9jtUKIDxYCCaPGGwiOUCuCScjV7exFPVX6kp+RcoIytDHpR qVqh4OK2MIjnw+6L2p9iEwV+Pb4BHpKm5xCrCCQgcMBNUtdpDZu1UdWeMBI8kYhDmWgEC2Xziz4 9wl/f+yHf66+lg1/K4yrwb3mf2fg= X-Google-Smtp-Source: AGHT+IGti6ygUSDEPOvtPmC0MgdDJOv2wcoxn3kUfSFBqhd1GW2v1xZ73SkeVnsrMBGe5103du1tiR8KtkaqbPo5PtA= X-Received: by 2002:a05:6214:4119:b0:6b4:b179:8eea with SMTP id 6a1803df08f44-6bb5597d3bamr131210226d6.3.1722377085642; Tue, 30 Jul 2024 15:04:45 -0700 (PDT) MIME-Version: 1.0 References: <20240725232813.2260665-1-nphamcs@gmail.com> <20240725232813.2260665-2-nphamcs@gmail.com> <20240730033929.GB2866591@cmpxchg.org> In-Reply-To: From: Nhat Pham Date: Tue, 30 Jul 2024 15:04:34 -0700 Message-ID: Subject: Re: [PATCH 1/2] zswap: implement a second chance algorithm for dynamic zswap shrinker To: Yosry Ahmed Cc: Johannes Weiner , akpm@linux-foundation.org, linux-mm@kvack.org, kernel-team@meta.com, linux-kernel@vger.kernel.org, flintglass@gmail.com, Chengming Zhou , Shakeel Butt Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: A22E5C002B X-Stat-Signature: uag8u3gc4optc3kaqdopwgy4rgr34tce X-Rspam-User: X-HE-Tag: 1722377086-394015 X-HE-Meta: U2FsdGVkX1+3dohl+vnLs07y32Rlm+fImVPGDDJT7cgZFSaevGq01lq7GrgMEl65KkL+Ikbli58pjfs7FDoTIvyF+Cmw7gXlSsRCnGf9OGJehq7+1iXktU01vuNjWB1O59GhaP3wF1ePwaHRqAQICqng/WlOackrf+hUDzRFmUt3mFtGGQTzLdL2LGr8zFHasHzvCA6PnvYCareHR9feQWVimdKG/XkngwTDDm6fQSPG+TzKv8vqMHdaCeH5M+iB5SL39KNKZAoH1aZMFCy3YrYxKS8ZM2BddiTvRvwmjEg2F4MzanCnyd/hdDjBFLqrRPLJICF6vLEa4PgZC84AKNjjZ3OV7/qIjFbKQt8t7k/7flWDZuUfj+vr3f7hZv/poBrWGp+IQteqCd6lW+1iSbxLkGL261Meaq4fiYRBhEpE1z3sEn1Fe5OBpxUF3wi2n8BWfQzxKvpiMJSFaQgPmptOYigMAqCwmNzpCht+9C7xz8pHLqydPpKq7yf/0XtLmQXvbgeK2NfNFzNIv5GqO40qS7baebuIA+HdiOGQMcrVDHWQ95PTYuGVOu0HkGSTXwWAlMpR4E+0qi6OAWhLnkuz/bhh9HXD/FHCsxF/2mPttMO6bFJBTM7dgYCDSpr5nxyAjGy4HEs4x8T3t/7kCYz8FSvoLZlg3MPFb5t5bEcqmcE4+igsc6+p5X1vZViKLEaDbeA4ywtZX9Yoqcb1JPxRRHCSts77Z5AGZR98gnsdHUp4wtzqcc4Lk/nH89UyAZy98gs07GI08sIHOLi9016SAzeb29EIHd2djgbo0TAYGuLYRCUGPbw9JRKYcI9bd/miSxkSgLfekcysMi8otjYmROweHEzOOn8N2y2UkIBHP0TwMXna5tl3ut0LUMoThzVMqiUXWXQpirkZm5York0i1/LLpkERqMDmXsPZfT9oiMt6XEmszsNUM4AvWMOaIT1MHtG+5YXdE/c84ms lls/QVEz kSJ9p+T4dPvAi6UVQ8szExyRS7xMWyA6UXxoV+cEpo2PpM52IW3/TeluCUfwUQ1GSND76HwglvIaaBP+pkajmrLz7ojDT0pWN9EK1gCOSW4oLg1KP++jEQlWSn9XeBgvGa0H2KJd8HICydtiJ7JBwLCcBwK3V09rx7oRgjTSvxJWiQSBt8INS4ZiwsjBwjgDZiCP0rOhPVNyrp4hdJjNppi+k/WZx2jdnJr0Ohk9cfcrYEITTBJzfC1ez7zphvgCtR3a4ze1mr74U1AP1Si1V2GX/j1J0774VeeB9ugoR/elanVs/bmql6Q03jRzzqwSgAp5R X-Bogosity: Ham, tests=bogofilter, spamicity=0.030094, 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 Tue, Jul 30, 2024 at 11:46=E2=80=AFAM Yosry Ahmed wrote: > > I also think it's important to clarify that there are two mechanisms > that control the writeback rate with this patch, the reference bit > proportional slowdown (protecting against writeback of recently > swapped out pages), and nr_swapins protection (feedback from swapins > of recently written back pages). Regarding this - perhaps I wasn't being clear, but I did include both in the changelog. The latter is this paragraph: "We will still maintain the count of swapins, which is consumed and subtracted from the lru size in zswap_shrinker_count(), to further penalize past overshrinking that led to disk swapins. The idea is that had we considered this many more pages in the LRU active/protected, they would not have been written back and we would not have had to swapped them in." I also replicate this comment in the nr_swapin explanation - see struct zswap_lruvec_state. Same goes with the second chance algorithm - I did briefly explain it in shrink_memcg_cb(), as well as the changelog. > > Maybe we can move things around to make it more obvious how these > mechanisms work hand in hand, or have a comment somewhere describing > the writeback mechanism. Hmm let me add some documentation for this near zswap_shrinker_{scan|count}() definitions: