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Wed, 08 Nov 2023 02:25:30 -0800 (PST) MIME-Version: 1.0 References: <1691402476-4838-1-git-send-email-hyeongtak.ji@gmail.com> <20231107183346.GA3789583@cmpxchg.org> In-Reply-To: <20231107183346.GA3789583@cmpxchg.org> From: Hyeongtak Ji Date: Wed, 8 Nov 2023 19:25:20 +0900 Message-ID: Subject: Re: [PATCH] mm/vmscan: consider previously reclaimed pages in shrink_lruvec() To: Johannes Weiner Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hyeongtak Ji Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: C10AC120002 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: gbh7m9ekftauubdoakszy7er5no14sbc X-HE-Tag: 1699439131-414922 X-HE-Meta: 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 loxHeuob YPCQwRjpPaalahB8VeQseFGFdUQ6hlYlxLqWPqoCX669TtKUMfvZhif7x/dXwSfbIRLzyTuPwF3pZqtFA1aLMYOu2riItyKpi8HknGJiJngnTupWyiPmeHCcTpyf/TpJTpuM9vBhqmrfuJbOVXZeRjptbrACfDte67UYVmldHj2f/HBW0F/Nj9c8FZOKNowuUKMoF1X3QXCnMeZuWsGQ5GXySSVokqTuH6RiS39okD8u+yHe8O513lL0JGRD6jsPvKZA9tVN95MGzTDd9b5nSXD7sPbU02GTiKyr5nPCytGSBx5/ZtFgQMpunCOs5KxdrPzo5voxlMh/x9BN29+DMxDh5IGczEDwErmgefhqTS5J75hGVTpSFrz914h6BTYxPd6YOKoT4Ke1XZ31kl6GlYpTU/+Q/QCX+3A6XKUEHzT82jnAjgqcPy1k/EnhsRjl3VP8pPYJbbw4C1FK48J33T0iRGVu44ZH8CwQ/1ygaV7CtYNs= X-Bogosity: Ham, tests=bogofilter, spamicity=0.002527, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hello, Thank you for your reply. On Wed, Nov 8, 2023 at 3:33=E2=80=AFAM Johannes Weiner = wrote: > > On Mon, Aug 07, 2023 at 07:01:16PM +0900, Hyeongtak Ji wrote: > > shrink_lruvec() currently ignores previously reclaimed pages in > > scan_control->nr_reclaimed. This can lead shrink_lruvec() to reclaimin= g > > more pages than expected. > > > > This patch fixes shrink_lruvec() to take into account the previously > > reclaimed pages. > > Do you run into real world issues from this? The code has been like > this for at least a decade. > I believed this was merely a misinitialization that resulted in shrink_lruvec() reclaiming more pages than intended. However, I do acknowledge that there have not been any real world issues arising from this behavior. > It's an intentional choice to ensure fairness across all visited > cgroups. sc->nr_to_reclaim is 32 pages or less - it's only to guard sc->nr_to_reclaim can be larger than 32 (e.g., about 5K) in the case that I was worrying about. kswapd_shrink_node() in mm/vmscan.c sets the value and it is passed down to shrink_lruvec(). > against extreme overreclaim. But we want to make sure we reclaim a bit > from all cgroups, rather than always hit the first one and then bail.