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[109.81.87.166]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-499a9aa1594sm36622845e9.0.2026.08.18.23.55.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Aug 2026 23:55:51 -0700 (PDT) Date: Wed, 19 Aug 2026 08:55:50 +0200 From: Michal Hocko To: Andrew Morton Cc: Matthew Wilcox , Lance Yang , david@kernel.org, leon.hwang@linux.dev, linux-mm@kvack.org, muchun.song@linux.dev, osalvador@suse.de, linux-kernel@vger.kernel.org Subject: Re: [PATCH] hugetlb: add cond_resched() to __unmap_hugepage_range() Message-ID: References: <20260818115526.654d7311366b66cd031c67e4@linux-foundation.org> <20260818221858.86452-1-lance.yang@linux.dev> <20260818162430.0a51522ac9bd671cce62650f@linux-foundation.org> <20260818165938.243ead051f792ee1519a5c79@linux-foundation.org> 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 Content-Disposition: inline In-Reply-To: <20260818165938.243ead051f792ee1519a5c79@linux-foundation.org> On Tue 18-08-26 16:59:38, Andrew Morton wrote: > On Wed, 19 Aug 2026 00:46:09 +0100 Matthew Wilcox wrote: > > > On Tue, Aug 18, 2026 at 04:24:30PM -0700, Andrew Morton wrote: > > > On Wed, 19 Aug 2026 06:18:58 +0800 Lance Yang wrote: > > > > > > > >> > > > > > >> > That's pretty bad behavior and we might want to fix it in earlier > > > > >> > kernels. Is PREEMPT_NONE effectively dead in 6.18.x and its > > > > >> > existing users? > > > > >> > > > > > >> > If yes, we do want to fix older kernels then we should merge this. > > > > >> > > > > > >> > > > > >> Okay, but that would be stable-only fixes? > > > > > > > > > >Not understanding. > > > > > > > > > >Maybe you refer to adding a patch to -stable but not to -linus? That's > > > > >against the -stable rules > > > > >(Documentation/process/stable-kernel-rules.rst). > > > > > > > > Since cond_resched() is a scheduling no-op under LAZY/FULL anyway (only > > > > the __might_resched() debug check remains), why not take this upstream > > > > with Cc: stable? > > > > > > I think so - as long as PREEPMT_NONE exists we should support it as > > > well as we can. If the day comes that PREEMPT_NONE is removed, then we > > > get to remove lots of cond_resched()s. mm/ has 200 of the things. > > > > > > > Mainline scheduling stays unchanged, and stable can pick it up for old > > > > PREEMPT_NONE kernels. wdyt? > > > > > > Addressing this issue in older kernels is another reason. > > > > That is not the direction that the scheduler developers wish us to take. > > Well back luck. > > "Packet receive timeouts were traced to sparse HugeTLB unmapping in > production". Do sched developers have a proposal to fix that in > year-old kernels? Yes, do not use PREEMPT_NONE in anything that is latency sensitive. It makes very little sense to add more cond_resched, just to be removed later. -- Michal Hocko SUSE Labs