Re: [PATCH v1 09/36] mm/mm_init: make memmap_init_compound() look more like prep_compound_page()
From: Lorenzo Stoakes <hidden>
Date: 2025-08-28 14:55:49
Also in:
dri-devel, intel-gfx, io-uring, kvm, linux-crypto, linux-ide, linux-iommu, linux-kselftest, linux-mips, linux-mm, linux-mmc, linux-riscv, linux-s390, linux-scsi, lkml, netdev, virtualization
On Thu, Aug 28, 2025 at 12:01:13AM +0200, David Hildenbrand wrote:
Grepping for "prep_compound_page" leaves on clueless how devdax gets its compound pages initialized. Let's add a comment that might help finding this open-coded prep_compound_page() initialization more easily. Further, let's be less smart about the ordering of initialization and just perform the prep_compound_head() call after all tail pages were initialized: just like prep_compound_page() does. No need for a comment to describe the initialization order: again, just like prep_compound_page().
Wow this is great, thank you for putting a quality comment for this and thinking of this :) We have too much 'special case you just have to know' stuff sitting around, so this kind of thing is always great to see.
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Signed-off-by: David Hildenbrand <redacted>
LGTM, so: Reviewed-by: Lorenzo Stoakes <redacted>
quoted hunk ↗ jump to hunk
--- mm/mm_init.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-)diff --git a/mm/mm_init.c b/mm/mm_init.c index 5c21b3af216b2..df614556741a4 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c@@ -1091,6 +1091,12 @@ static void __ref memmap_init_compound(struct page *head, unsigned long pfn, end_pfn = head_pfn + nr_pages; unsigned int order = pgmap->vmemmap_shift; + /* + * We have to initialize the pages, including setting up page links. + * prep_compound_page() does not take care of that, so instead we + * open-code prep_compound_page() so we can take care of initializing + * the pages in the same go. + */ __SetPageHead(head); for (pfn = head_pfn + 1; pfn < end_pfn; pfn++) { struct page *page = pfn_to_page(pfn);@@ -1098,15 +1104,8 @@ static void __ref memmap_init_compound(struct page *head, __init_zone_device_page(page, pfn, zone_idx, nid, pgmap); prep_compound_tail(head, pfn - head_pfn); set_page_count(page, 0); - - /* - * The first tail page stores important compound page info. - * Call prep_compound_head() after the first tail page has - * been initialized, to not have the data overwritten. - */ - if (pfn == head_pfn + 1) - prep_compound_head(head, order); } + prep_compound_head(head, order); } void __ref memmap_init_zone_device(struct zone *zone, --2.50.1