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 9F7E2399354; Tue, 29 Sep 2026 07:24:12 +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=1790666653; cv=none; b=YJFavDYrP7T8O+ozRq26y1oAhTcX6NmJVpmI3BorK09mo+Z0QoeA4iqTOtRFIXRrZIvbO3NIlrtcwtNGfiaQ93NQta+//QSJKeEbEmK87ZSQGemNGVs8r+4rz9QEDBNlsRLoGbsotWvywKa+S/1jwwOtaFz+zUqSIq5unonA6lI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790666653; c=relaxed/simple; bh=9OJFrXkMPFlQtVTNM1EYM7wZo8LqpsR+r5Hv7zoLFlw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=PKpfluoGqmCVvK43Xi7nVjOMVUbSN38eGABUHcNrCMTDgid/wIEGZkkSqilzQOqkhjoQq6tmuJyGqmtG/oPJDprDmdUyZelM7OhGerD/SnpQCTgvF9QgweutlmZGON2Ln0ZGuR5doe3EmPo/fCHMI0z5mP6MmlDSbctE/wf9O8Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ibkey2yU; 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="ibkey2yU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DE16C1F000FF; Tue, 29 Sep 2026 07:24:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790666652; bh=yvxJPj3k2vjV6D8HUDd8QkKGWeBMIhXhJhVwkCPhP3Q=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ibkey2yUqqbiVM76d/2jZTGyjIdUdz2aZM6YaiTOTz9joywkD+nsB2wdU5GPHSSHW Uxe6UNjvfBnxPaLAJiLIH+gsRzsY2K3p6sj1jwCatttOSR5PmQJWeYyMS7R0gTipDx 91toSUwKUs91yGhn4NOpNTCFOAR4QjdipsKpKZKrVdgP4YFHgv2ipVUjpAgmvec1Sg nwUgjtnXkrBuf1mAFgFG+g0dFlvx/XpzAYRP1+O1d6y22DmRT+IkA3jEDVM8r9eqqu gWm26joLY6CvegjTpmEF/XdyrAUPtvOP2B8YcOfRZfiDX7H+Xr/UGrRS9OQkV2HyLu Y9EqZQaCIOopw== Message-ID: Date: Tue, 29 Sep 2026 09:24:06 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 05/12] mm/sparse-vmemmap: prepare DAX vmemmap population for compound page orders To: Muchun Song , Andrew Morton , Oscar Salvador , Madhavan Srinivasan , Michael Ellerman , Jonathan Corbet Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-doc@vger.kernel.org, Muchun Song , Lorenzo Stoakes , Mike Rapoport , Qi Zheng , Nicholas Piggin , Christophe Leroy , Randy Dunlap , Lance Yang References: <20260927025441.741633-1-songmuchun@bytedance.com> <20260927025441.741633-6-songmuchun@bytedance.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/27/26 04:54, Muchun Song wrote: > Device DAX still uses vmemmap_populate_compound_pages() to populate its > compound-page vmemmap mappings. That helper allocates the head and first > tail vmemmap pages explicitly, then reuses the first tail page for the > remaining tail page mappings. > > Device DAX is being moved to the section-based vmemmap optimization > infrastructure, but it cannot switch to the generic section-based > population path yet. Once a later patch records the DAX compound page > order in section metadata, DAX head and first-tail PFNs can look > optimizable to the generic helpers as well. > > Add a DAX-specific population flag for this transition. It keeps DAX Well, you're not adding flag, your reusing an existing one and renaming it? And then you're specifying it on more paths. [...] > mm/sparse-vmemmap.c | 27 +++++++++++++++------------ > 1 file changed, 15 insertions(+), 12 deletions(-) > > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c > index e4dae98ba7f8..2457ea2c6dca 100644 > --- a/mm/sparse-vmemmap.c > +++ b/mm/sparse-vmemmap.c > @@ -35,8 +35,8 @@ > /* > * Flags for vmemmap_populate_range and friends. > */ > -/* Get a ref on the head page struct page, for ZONE_DEVICE compound pages */ > -#define VMEMMAP_POPULATE_PAGEREF 0x0001 > +/* Vmemmap population for ZONE_DEVICE compound pages */ > +#define VMEMMAP_POPULATE_DAX 0x0001 Cleaner. > > #include "internal.h" > #include "mm_init.h" > @@ -243,13 +243,17 @@ static inline struct page *vmemmap_shared_tail_page(unsigned int order, > #endif > > static __meminit void *vmemmap_alloc_pte(unsigned long pfn, int node, > - struct vmem_altmap *altmap) > + struct vmem_altmap *altmap, unsigned long flags) > { > struct zone *zone; > struct page *page; > const unsigned int order = pfn_to_section_compound_order(pfn); > > - if (!vmemmap_optimizable_pfn(pfn)) > + /* > + * Device DAX still relies on vmemmap_populate_compound_pages() for > + * head/first-tail allocation and tail-page reuse. > + */ > + if (!vmemmap_optimizable_pfn(pfn) || flags & VMEMMAP_POPULATE_DAX) > return vmemmap_alloc_block_buf(PAGE_SIZE, node, altmap); > > zone = pfn_to_zone(pfn, node); > @@ -271,7 +275,7 @@ static pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, in > pte_t entry; > > if (ptpfn == (unsigned long)-1) { > - void *p = vmemmap_alloc_pte(pfn, node, altmap); > + void *p = vmemmap_alloc_pte(pfn, node, altmap, flags); > > if (!p) > return NULL; > @@ -286,7 +290,7 @@ static pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, in > * and through vmemmap_populate_compound_pages() when > * slab is available. > */ > - if (flags & VMEMMAP_POPULATE_PAGEREF) > + if (flags & VMEMMAP_POPULATE_DAX) > get_page(pfn_to_page(ptpfn)); > } > entry = pfn_pte(ptpfn, PAGE_KERNEL); > @@ -546,6 +550,7 @@ static int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn, > unsigned long size, addr; > pte_t *pte; > int rc; > + unsigned long flags = VMEMMAP_POPULATE_DAX; const and at the top? -- Cheers, David