From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4E8F64964F for ; Thu, 9 Jul 2026 13:06:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783602366; cv=none; b=h4YpexhBl9iHTDj9Ia+4C09D2/EviqZjjg2ZFh1rdnxs0HD+EP+m/73dg/6UeNp1ESUW+vkO8FidBli6KT+RnGsw3gfZZmBufCWYXK8e4Uv+i+YOltanDKPeOVgajmzkK76xxpYyBlZgvduxA7mBbGTfgPTt3boHi16tco6A6IA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783602366; c=relaxed/simple; bh=WXzyWHEYaNYhP9xbzHeV/RPkh8VF5YDeOC5AuVxNOnQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=TKQjz/ekY6ffXud5offhB1ZQVZwaHtnzW14P7mrvsXHN9Yp3AMtzKzNqBaHOa2DK/wJnlj7ueU8GjvFlIo1gQ7d0pDInZPoDcc1LYgibeacVksJz2aZnWw8VypxTsjEOsUAT59lb+ZABv9Hl0QEt27pJPfPPpKFTJ3yTQ7255Pc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AfhJDsXr; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="AfhJDsXr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 373911F000E9; Thu, 9 Jul 2026 13:06:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783602365; bh=gHoAaqin36BM7n0JyPwQOiJA2k5bERfSNEoUEt4tWaA=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=AfhJDsXr9Jlh7JbWr6kTwPdZ2rinAltVe3gCbsphpBZwQhIWOHoS/OJLKDv0SaM92 usoZnqAhNKrNYTsB8hSLGLOr0ZTAR2D6pN8PAXIR72BWQlLNUWYfaaITPLUozVolb5 y6Xn4VjC6+jdUuFQQCYvpkGitYNqGB15TRPQ5Z8IjzLHy7dIVyMB6+mxf+yIe0pQIV 6w+7TzuKTqWytZekZ4phDVnKW1R9cNpAkyC84VmdpX36o975jUoHhuRahpVHMOaNfa I9I2KXf4OA6tci8sf8im68/NTyxsxsypyy0uGqO8rRbPzxv3RTWsjeBQdr7tD5JITe TCOQkjDEreubA== Date: Thu, 9 Jul 2026 16:05:58 +0300 From: Mike Rapoport To: Muchun Song Cc: Muchun Song , Andrew Morton , Oscar Salvador , David Hildenbrand , linux-mm@kvack.org, Vlastimil Babka , Lorenzo Stoakes , Michal Hocko , linux-kernel@vger.kernel.org Subject: Re: [PATCH 04/17] mm/mm_init: skip initializing shared vmemmap tail pages Message-ID: References: <20260702093821.2740183-1-songmuchun@bytedance.com> <20260702093821.2740183-5-songmuchun@bytedance.com> <2306829C-A66D-41F2-B5F7-1C164A7FF757@linux.dev> 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: <2306829C-A66D-41F2-B5F7-1C164A7FF757@linux.dev> On Thu, Jul 09, 2026 at 08:31:31PM +0800, Muchun Song wrote: > > On Jul 9, 2026, at 18:45, Mike Rapoport wrote: > > On Thu, Jul 02, 2026 at 05:38:08PM +0800, Muchun Song wrote: > >> memmap_init_range() initializes every struct page in the target range. > >> For compound pages with vmemmap optimization, the tail struct pages are > >> backed by a shared vmemmap page. > >> > >> Initializing those tail struct pages would overwrite the shared > >> vmemmap page contents, so users such as HugeTLB have to open-code > >> follow-up handling to restore the metadata afterwards. > >> > >> Use the section's compound page order to detect struct pages that fall > >> into the shared tail vmemmap range and skip their initialization in > >> memmap_init_range(). Still initialize the pageblock migratetypes for > >> the skipped range so the surrounding setup remains intact. > >> > >> This is a preparatory change for consolidating handling across users of > >> vmemmap optimization, and it also avoids redundant initialization of > >> shared tail vmemmap pages during early boot. > >> > >> Signed-off-by: Muchun Song > >> --- > >> include/linux/mmzone.h | 4 ++++ > >> mm/internal.h | 16 ++++++++++++++++ > >> mm/mm_init.c | 25 +++++++++++++++++++------ > >> 3 files changed, 39 insertions(+), 6 deletions(-) > >> > >> @@ -673,19 +673,21 @@ static inline void fixup_hashdist(void) > >> static inline void fixup_hashdist(void) {} > >> #endif /* CONFIG_NUMA */ > >> > >> -#if defined(CONFIG_ZONE_DEVICE) || defined(CONFIG_DEFERRED_STRUCT_PAGE_INIT) > >> static __meminit void pageblock_migratetype_init_range(unsigned long pfn, > >> - unsigned long nr_pages, int migratetype, bool atomic) > >> + unsigned long nr_pages, int migratetype, bool isolate, bool atomic) > > > > What is isolate parameter for? > > I've re-examined the code, and you're right that the isolate parameter is technically > redundant for our current use case, as memmap_init_zone_range() passes false. > > The rationale behind keeping it is future-proofing. The ultimate goal of a generic > HVO is to support arbitrary huge pages, not just HugeTLB. I decoupled this as a > parameter to prevent potential regressions down the road; if a developer leverages > this for other huge page types in the future, they won't inadvertently break > things by forgetting to update a hardcoded false in init_pageblock_migratetype(), > especially since memmap_init_range() natively accepts an isolate parameter. > > Of course, we could also just delete this parameter for now and add it back later if > needed. I think both approaches work. > > Which way are you leaning? I'd drop it for now and would revisit when there would be a new HVO user. Even one boolean means it's hard to tell from a call site what is the intention of the flag, two make it completely confusing :) > >> { > >> const unsigned long end = pfn + nr_pages; > >> > >> for (pfn = pageblock_align(pfn); pfn < end; pfn += pageblock_nr_pages) { > >> - init_pageblock_migratetype(pfn_to_page(pfn), migratetype, false); > >> + init_pageblock_migratetype(pfn_to_page(pfn), migratetype, isolate); > >> +#ifdef CONFIG_SPARSEMEM > >> if (!atomic && IS_ALIGNED(pfn, PAGES_PER_SECTION)) > >> +#else > >> + if (!atomic && IS_ALIGNED(pfn, MAX_FOLIO_NR_PAGES)) > >> +#endif > > > > Let's trigger cond_resched() on some defined number of iterations or some > > memory size chunk, e.g PAGES_PER_128M or even PAGES_PER_1G. > > Yes, that's for the best. I was really struggling to choose a suitable macro > for this earlier, but I realized it's a difficult thing to get right. I'm leaning > toward selecting PAGES_PER_1G instead. Yeah, PAGES_PER_1G makes sense to me too. > Muchun, > Thanks. > > > > >> cond_resched(); -- Sincerely yours, Mike.