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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1uknl4-00000002Qkb-400y; Sat, 09 Aug 2025 17:53:30 +0000 Date: Sat, 9 Aug 2025 18:53:30 +0100 From: Matthew Wilcox To: Andrew Morton Cc: "Subrata Nath (Nokia)" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] mm: prevent RCU stalls in kswapd by adding cond_resched() Message-ID: References: <20250809103845.21ca58f0a97c0c1f61c0879c@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250809103845.21ca58f0a97c0c1f61c0879c@linux-foundation.org> X-Stat-Signature: jjf3qsf5w1cbmjrdr997mgri57ti54b1 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: A7E5B180004 X-Rspam-User: X-HE-Tag: 1754762016-706680 X-HE-Meta: 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 Q7dBYW02 mYwa5TuVu6VOXusXTNyQlvk6VAR6h5adhZJatmLvfMaYdhZbLVQqf/7CBnw1PL96iwt+r/rlq/6K5frVR6bijqxzIgAuB9VJf7YxGR+eXMNzDSk2Zqimml4dgpLB9uEkljABGXAxby4nQcp0+vbx9o5k6ivsW0GJL5HsuCpU/yFNAHagT5LgvcfqZ+hBh5uO3a8IjkXTPR+uCWNkh09aYHWQfjD2c+KLKRilpRosb6n0+HNARoaaUM0jnqweY9dJEfNqp75+TEssczCP3S/aldrsHPxOimcCG+toGmA383AbxrgEs/UQycLT6FYo7Hbum2arENXu1H3aa0L7IjiPuGV42Ua6tzoIIPaWVTkQoJGWpmOy+1VDbBJj19g== 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: On Sat, Aug 09, 2025 at 10:38:45AM -0700, Andrew Morton wrote: > On Sat, 9 Aug 2025 16:09:12 +0100 Matthew Wilcox wrote: > > > On Sat, Aug 09, 2025 at 11:59:16AM +0000, Subrata Nath (Nokia) wrote: > > > Fix this by adding cond_resched() after all spinlock release points > > > in page_vma_mapped_walk() and in the main loop of shrink_zones(). > > > These calls, placed outside spinlock-held sections, allow voluntary > > > scheduling and ensure timely quiescent state reporting, avoiding > > > prolonged RCU stalls. > > > > No. We're removing cond_resched(). See > > https://lore.kernel.org/linux-mm/87cyyfxd4k.ffs@tglx/ > > and many many other emails over the past few years. > > tglx's email was sent two years ago. ... and there has been much progress since then. Most recently, https://lore.kernel.org/all/20250225035516.26443-1-boqun.feng@gmail.com/ This report is not from a recent kernel. Subrata was good enough to include: Based on: v6.1.128 and I think it is very much on them to prove that this is still a problem in 2025.