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Tue, 31 Mar 2026 09:44:31 -0700 (PDT) Received: from [2a00:79e0:2eb0:8:7c3f:a173:3e15:575a] ([2a00:79e0:2eb0:8:7c3f:a173:3e15:575a]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c76917bacc2sm9459387a12.26.2026.03.31.09.44.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Mar 2026 09:44:31 -0700 (PDT) Date: Tue, 31 Mar 2026 09:44:30 -0700 (PDT) From: David Rientjes To: Shakeel Butt cc: Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Petr Mladek , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [patch v3] mm, page_alloc: reintroduce page allocation stall warning In-Reply-To: <69cb3957.5d0a0220.93499.af4cSMTPIN_ADDED_BROKEN@mx.google.com> Message-ID: References: <30945cc3-9c4d-94bb-e7e7-dde71483800c@google.com> <231154f8-a3c3-229a-31a7-f91ab8ec1773@google.com> <58a10940-e44c-a120-dd6e-ee9f480c4946@google.com> <371c86c8-1d47-bd70-b74c-769842718b1f@google.com> <69cb3957.5d0a0220.93499.af4cSMTPIN_ADDED_BROKEN@mx.google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII On Mon, 30 Mar 2026, Shakeel Butt wrote: > > Previously, we had warnings when a single page allocation took longer > > than reasonably expected. This was introduced in commit 63f53dea0c98 > > ("mm: warn about allocations which stall for too long"). > > > > The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't > > warn about allocations which stall for too long") because it was possible > > to generate memory pressure that would effectively stall further progress > > through printk execution. > > > > Page allocation stalls in excess of 10 seconds are always useful to debug > > because they can result in severe userspace unresponsiveness. Adding > > this artifact can be used to correlate with userspace going out to lunch > > and to understand the state of memory at the time. > > > > There should be a reasonable expectation that this warning will never > > trigger given it is very passive, it will only be emitted when a page > > allocation takes longer than 10 seconds. If it does trigger, this > > reveals an issue that should be fixed: a single page allocation should > > never loop for more than 10 seconds without oom killing to make memory > > available. > > > > Unlike the original implementation, this implementation only reports > > stalls once for the system every 10 seconds. Otherwise, many concurrent > > reclaimers could spam the kernel log unnecessarily. Stalls are only > > reported when calling into direct reclaim. > > > > Acked-by: Vlastimil Babka (SUSE) > > Signed-off-by: David Rientjes > > Reviewed-by: Shakeel Butt > > I am hoping that the reason you are reintroducing these warnings is > because you already are seeing such cases in your production > environment. Do you have anything interesting to share? > We don't have this patch in our production environment (yet). We've been stress testing allocations for page faults with lots of concurrent skb allocations that can keep us persistently below the per-zone min watermarks and hope that this patch will shed some light on some unresponsiveness issues that we've encountered if/when it happens.