From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-170.mta0.migadu.com (out-170.mta0.migadu.com [91.218.175.170]) (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 8770E36E48B for ; Tue, 14 Jul 2026 02:45:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.170 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783997133; cv=none; b=afkPnzNidF1UwHrC/vwUbVD4Jy9qBgyPx81YwR3PuxkYwTiCGnj5vGu2B1CjFg6DXF0xWPLJ1A89czWLSFHqXCgs0ugYM1MT1Zvf4pzA46GKprSYN0oZuXsx/yc3K3mbLdMhRn98n5PU+FVU0m4WRw21hnMxI9m+wzfv138pcAM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783997133; c=relaxed/simple; bh=5MAFloAc3GTiCVj/jV42l3HY1PvEXBDwzcrBAvGk5LM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=tuXve5K52t5nppftD0GF9koRhws8y727Pyq2gIkpWJBRkfw1morOKf91jHO8Pidi1/Ra10plJ1V5fk2M2Y3sPT4ts8uT6aAGotihA27rDL23Jx7l0W9Hw7oVpt53mH21RiTrysPlxVsfROB3q1h/PCL2XS3cy97dgYivOPcWxbs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=OMJ2w4Zw; arc=none smtp.client-ip=91.218.175.170 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="OMJ2w4Zw" Message-ID: <993afd58-e503-46aa-acaf-19243b0d147c@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1783997117; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=nb7XE0WKxPNCmW2jzzoEfyvfKdOTIP2EGQX42DdHNL8=; b=OMJ2w4ZwurgTTryrGfFSYG399nNWFddIFP0IbpfcqzSmC+cengYkbS2Uj3xx2QK/1Pozab 5yb3IX4IJBBcgNeFk2ad9gLwpxighNPp65I9K7S8C9OjYD3sMQZWQJt/T49WYCKGx5++Qf JOHHqjCt1680A1SOSdk8++/jXsNzsRw= Date: Tue, 14 Jul 2026 10:44:47 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v6 2/8] mm: factor zone-device page init helpers out of __init_zone_device_page To: Li Zhe Cc: linux-arch@vger.kernel.org, linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, apopple@nvidia.com, arnd@arndb.de, balbirs@nvidia.com, bp@alien8.de, dave.hansen@linux.intel.com, david@kernel.org, kees@kernel.org, mingo@redhat.com, rppt@kernel.org, tglx@kernel.org References: <20260709112520.24857-1-lizhe.67@bytedance.com> <20260709112520.24857-3-lizhe.67@bytedance.com> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Muchun Song In-Reply-To: <20260709112520.24857-3-lizhe.67@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 2026/7/9 19:25, Li Zhe wrote: > memmap_init_zone_device() currently mixes refcount policy and core > ZONE_DEVICE page setup in a single helper. > > Factor the refcount-reset predicate into pagemap_resets_refcount(), move > the common page initialization into __zone_device_page_init(), and wrap > the existing slow path in zone_device_page_init_slow(). Hi, Sorry if this has been discussed before, but I'm still curious—what is the significance of the 'slow' suffix here? I don't think I quite understand why this is called the 'slow path' here. Is there also a 'fast path' for initializing struct page? Thanks. > > This keeps the slow-path behaviour unchanged and gives later patches > reusable helper boundaries. > > No functional change intended. > > Signed-off-by: Li Zhe > Reviewed-by: Mike Rapoport (Microsoft) > --- > mm/mm_init.c | 56 ++++++++++++++++++++++++++++++++++------------------ > 1 file changed, 37 insertions(+), 19 deletions(-) > > diff --git a/mm/mm_init.c b/mm/mm_init.c > index 95808ab5cfdb..5fccfbacf855 100644 > --- a/mm/mm_init.c > +++ b/mm/mm_init.c > @@ -1005,11 +1005,37 @@ static void __init memmap_init(void) > } > > #ifdef CONFIG_ZONE_DEVICE > -static void __ref __init_zone_device_page(struct page *page, unsigned long pfn, > +/* > + * Return true when the free path for this pagemap type restores the page > + * refcount to 1, so memmap_init_zone_device() can keep the count set by > + * __init_single_page(). Otherwise initialize the refcount to 0 and leave > + * it to the allocator or pgmap callbacks to raise it when the page is > + * handed out again. > + */ > +static inline bool pagemap_resets_refcount(const struct dev_pagemap *pgmap) > +{ > + /* > + * MEMORY_DEVICE_GENERIC pages regain a refcount of 1 in the free > + * path. The remaining ZONE_DEVICE types start from 0 here and raise > + * the count again when the allocator or driver hands the page out. > + */ > + switch (pgmap->type) { > + case MEMORY_DEVICE_FS_DAX: > + case MEMORY_DEVICE_PRIVATE: > + case MEMORY_DEVICE_COHERENT: > + case MEMORY_DEVICE_PCI_P2PDMA: > + return false; > + case MEMORY_DEVICE_GENERIC: > + return true; > + } > + > + return true; > +} > + > +static void __ref __zone_device_page_init(struct page *page, unsigned long pfn, > unsigned long zone_idx, int nid, > struct dev_pagemap *pgmap) > { > - > __init_single_page(page, pfn, zone_idx, nid); > > /* > @@ -1028,23 +1054,15 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn, > */ > page_folio(page)->pgmap = pgmap; > page->zone_device_data = NULL; > +} > > - /* > - * MEMORY_DEVICE_GENERIC pages regain a refcount of 1 in the free > - * path. The remaining ZONE_DEVICE types start from 0 here and raise > - * the count again when the allocator or driver hands the page out. > - */ > - switch (pgmap->type) { > - case MEMORY_DEVICE_FS_DAX: > - case MEMORY_DEVICE_PRIVATE: > - case MEMORY_DEVICE_COHERENT: > - case MEMORY_DEVICE_PCI_P2PDMA: > +static void __ref zone_device_page_init_slow(struct page *page, > + unsigned long pfn, unsigned long zone_idx, int nid, > + struct dev_pagemap *pgmap) > +{ > + __zone_device_page_init(page, pfn, zone_idx, nid, pgmap); > + if (!pagemap_resets_refcount(pgmap)) > set_page_count(page, 0); > - break; > - > - case MEMORY_DEVICE_GENERIC: > - break; > - } > } > > /* > @@ -1090,7 +1108,7 @@ static void __ref memmap_init_compound(struct page *head, > for (pfn = head_pfn + 1; pfn < end_pfn; pfn++) { > struct page *page = pfn_to_page(pfn); > > - __init_zone_device_page(page, pfn, zone_idx, nid, pgmap); > + zone_device_page_init_slow(page, pfn, zone_idx, nid, pgmap); > prep_compound_tail(page, head, order); > set_page_count(page, 0); > } > @@ -1126,7 +1144,7 @@ void __ref memmap_init_zone_device(struct zone *zone, > for (pfn = start_pfn; pfn < end_pfn; pfn += pfns_per_compound) { > struct page *page = pfn_to_page(pfn); > > - __init_zone_device_page(page, pfn, zone_idx, nid, pgmap); > + zone_device_page_init_slow(page, pfn, zone_idx, nid, pgmap); > > if (IS_ALIGNED(pfn, PAGES_PER_SECTION)) > cond_resched(); > -- > 2.20.1