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Tue, 02 Jan 2024 07:21:46 -0800 (PST) Received: from dschatzberg-fedora-PF3DHTBV ([2620:10d:c091:500::7:66d9]) by smtp.gmail.com with ESMTPSA id da7-20020a05621408c700b0067f2c03d4adsm10072029qvb.100.2024.01.02.07.21.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Jan 2024 07:21:46 -0800 (PST) Date: Tue, 2 Jan 2024 10:21:44 -0500 From: Dan Schatzberg To: Yu Zhao Cc: Johannes Weiner , Roman Gushchin , Yosry Ahmed , Huan Yang , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Tejun Heo , Zefan Li , Jonathan Corbet , Michal Hocko , Shakeel Butt , Muchun Song , Andrew Morton , Kefeng Wang , SeongJae Park , "Vishal Moola (Oracle)" , Nhat Pham , Yue Zhao Subject: Re: [PATCH v5 2/2] mm: add swapiness= arg to memory.reclaim Message-ID: References: <20231220152653.3273778-1-schatzberg.dan@gmail.com> <20231220152653.3273778-3-schatzberg.dan@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 97EA840019 X-Stat-Signature: xefdjuf6odizknfg6ot1r1fhdjdoa9a5 X-Rspam-User: X-HE-Tag: 1704208907-639147 X-HE-Meta: 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 fXCDjFSq 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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: Hi Yu Zhao, Thanks for the feedback, sorry for the delayed response. On Thu, Dec 21, 2023 at 10:31:59PM -0700, Yu Zhao wrote: > On Wed, Dec 20, 2023 at 8:27 AM Dan Schatzberg wrote: > > > > ... > > The cover letter says: > "Previously, this exact interface addition was proposed by Yosry[3]." > > So I think it should be acknowledged with a Suggested-by, based on: > "A Suggested-by: tag indicates that the patch idea is suggested by the > person named and ensures credit to the person for the idea." > from > https://docs.kernel.org/process/submitting-patches.html#using-reported-by-tested-by-reviewed-by-suggested-by-and-fixes Sure, will do. > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index d91963e2d47f..aa5666842c49 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -92,6 +92,9 @@ struct scan_control { > > unsigned long anon_cost; > > unsigned long file_cost; > > > > + /* Swappiness value for reclaim. NULL will fall back to per-memcg/global value */ > > + int *swappiness; > > Using a pointer to indicate whether the type it points to is > overridden isn't really a good practice. > > A better alternative was suggested during the v2: > "Perhaps the negative to avoid unnecessary dereferences." > https://lore.kernel.org/linux-mm/dhhjw4h22q4ngwtxmhuyifv32zjd6z2relrcjgnxsw6zys3mod@o6dh5dy53ae3/ I did have a couple versions with a negative but it creates initialization issues where every instantiation of scan_control needs to make sure to initialize swappiness or else it will behave as if swappiness is 0. That's pretty error prone so using the pointer seemed the better approach. > Since only proactive reclaim can override swappiness, meaning it only > happens if sc->proactive is true, I think the best way to make it work > without spending much effort is create a helper as Michal suggest but > it should look like: > > sc_swappiness() > { > return sc->proactive ? sc->swappiness : mem_cgroup_swappiness(memcg); > } > > In this patchset, sc->swappiness really means > sc->proactive_swappiness. So it should be renamed accordingly. Helper aside, I disagree with this point about coupling with the proactive flag. The fact that the only user currently is proactive reclaim doesn't imply to me that the interface (in scan_control) should be coupled to the use-case. It's easier to reason about a swappiness field that overrides swappiness for all scans that set it regardless of the users.