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Mon, 13 Apr 2026 18:50:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776106251; bh=rdLqMR/Xr3fQS5U0jYUhu1Lu8JZHxK3+UfMlHMMb9T0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=DvdJDQe3oCG/gfgbw4UZP+je/1tx9raBCi0Fx3sjPOET7NPzV8JEnJSl0ggGBjtI1 hBhIC6ExWdLs8tBHuLezEk1U12agU+VHQnpht/UuNiSCyU+8VXWnc13JwUGl5zgr2U VjTV//cyB1Zcj0WObb4Osc+PRC81TE0WL/CE6EQvvb6fXUNa87P9GQiqBno6ZQmUFh v/4GZWWXcklcBfhYTXXJwMRjgxAsdPh+UL8SeN9/4z4Aygv6OZo6dpRQ+xjCtfYG0Y N3id4XvdsiushhArjrX8jdh1VCpQHVTLtkDeiAFmcATQBevco3PsThfZtGvxpi5yOj GMABa9pVDUYVg== Message-ID: <42ba7f13-846f-4150-8195-32a775bb6812@kernel.org> Date: Mon, 13 Apr 2026 20:50:41 +0200 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 06/49] mm/mm_init: fix uninitialized pageblock migratetype for ZONE_DEVICE compound pages To: Muchun Song , Mike Rapoport Cc: Muchun Song , Andrew Morton , Oscar Salvador , Michael Ellerman , Madhavan Srinivasan , Lorenzo Stoakes , Liam R Howlett , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Nicholas Piggin , Christophe Leroy , aneesh.kumar@linux.ibm.com, joao.m.martins@oracle.com, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org References: From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 4/13/26 15:57, Muchun Song wrote: > > >> On Apr 13, 2026, at 21:28, Mike Rapoport wrote: >> >> On Mon, Apr 13, 2026 at 06:07:44PM +0800, Muchun Song wrote: >>> >>> >>> >>> Of course not. >>> >>> >>> There are indeed many more cond_resched() than before, but I don’t have a >>> concise way to write it, so I took the easy way out. >>> >>> How about: >>> >>> diff --git a/mm/mm_init.c b/mm/mm_init.c >>> index 2d680636b67a..d13a2577c4c3 100644 >>> --- a/mm/mm_init.c >>> +++ b/mm/mm_init.c >>> @@ -683,7 +683,8 @@ static __meminit void pageblock_migratetype_init_range(unsigned long pfn, >>> >>> for (pfn = pageblock_align(pfn); pfn < end; pfn += pageblock_nr_pages) { >>> init_pageblock_migratetype(pfn_to_page(pfn), migratetype, isolate); >>> - cond_resched(); >>> + if ((pfn & (pageblock_nr_pages * 512 - 1)) == 0) >>> + cond_resched(); >> >> TBH, I don't know if 512 is the right number :) > > I picked this number out of thin air. I’m not sure as well. > >> >> pageblock boundary was a convenient point to have cond_resched() along with >> setting the migrate type. >> >> Here we might be able to squeeze more iterations between subsequent >> cond_resched() calls. > > Choosing an appropriate number is indeed difficult. We need to consider > both unnecessary cond_resched() calls and scheduling latency, and the > specific value also depends on the current CPU performance. At the very least, > I find it hard to choose a correct value. Since we all agree it should be larger > than 512, why not just pick 1024? I can't think of a good evaluation criterion > or selection method either. I think in some other code we just use section boundaries. -- Cheers, David