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[209.85.167.42]) by smtp.gmail.com with ESMTPSA id w16sm418342ljo.50.2021.01.12.09.35.51 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 12 Jan 2021 09:35:51 -0800 (PST) Received: by mail-lf1-f42.google.com with SMTP id b26so4574747lff.9 for ; Tue, 12 Jan 2021 09:35:51 -0800 (PST) X-Received: by 2002:a05:6512:2287:: with SMTP id f7mr28583lfu.40.1610472950962; Tue, 12 Jan 2021 09:35:50 -0800 (PST) MIME-Version: 1.0 References: <000000000000886dbd05b7ffa8db@google.com> <20210104124153.0992b1f7fd1a145e193a333f@linux-foundation.org> <20210112104425.GA8760@quack2.suse.cz> In-Reply-To: <20210112104425.GA8760@quack2.suse.cz> From: Linus Torvalds Date: Tue, 12 Jan 2021 09:35:34 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: kernel BUG at mm/page-writeback.c:LINE! To: Jan Kara Cc: Hugh Dickins , Andrew Morton , Matthew Wilcox , syzbot , Linux Kernel Mailing List , Linux-MM , syzkaller-bugs Content-Type: text/plain; charset="UTF-8" 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: On Tue, Jan 12, 2021 at 2:44 AM Jan Kara wrote: > > On Fri 08-01-21 18:04:21, Linus Torvalds wrote: > > > > Oh, and Michael Larabel (of phoronix) reports that that one-liner does > > something bad to a few PostgreSQL tests, on the order of 5-10% > > regression on some machines (but apparently not others). > > Do you have more details? From my experience (we do regular pgbench runs > for various kernels in various configs in SUSE) PostgreSQL numbers tend to > be somewhat noisy and more dependent on CPU scheduling and NUMA locality > than anything else. But it very much depends on the exact config passed to > pgbench so that's why I'm asking... No, I don't really have many more details. I don't have things like raw numbers or exact configurations, but Michael has been very responsive if you ask, so if you are interested, just email him at Michael Larabel . It wasn't NUMA - apparently the machines he saw this on were just plain consumer setups, and his larger machines didn't actually show the effect. But yes, I suspect it was some scheduling artifact, and probably just fairly random noise from just changing the scheduling pattern a bit. Linus