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Message-ID: <20250703233511.2028395-8-balbirs@nvidia.com>
Date: Fri, 4 Jul 2025 09:35:06 +1000
From: Balbir Singh <balbirs@...dia.com>
To: linux-mm@...ck.org
Cc: akpm@...ux-foundation.org,
linux-kernel@...r.kernel.org,
Balbir Singh <balbirs@...dia.com>,
Karol Herbst <kherbst@...hat.com>,
Lyude Paul <lyude@...hat.com>,
Danilo Krummrich <dakr@...nel.org>,
David Airlie <airlied@...il.com>,
Simona Vetter <simona@...ll.ch>,
Jérôme Glisse <jglisse@...hat.com>,
Shuah Khan <shuah@...nel.org>,
David Hildenbrand <david@...hat.com>,
Barry Song <baohua@...nel.org>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
Ryan Roberts <ryan.roberts@....com>,
Matthew Wilcox <willy@...radead.org>,
Peter Xu <peterx@...hat.com>,
Zi Yan <ziy@...dia.com>,
Kefeng Wang <wangkefeng.wang@...wei.com>,
Jane Chu <jane.chu@...cle.com>,
Alistair Popple <apopple@...dia.com>,
Donet Tom <donettom@...ux.ibm.com>
Subject: [v1 resend 07/12] mm/memremap: add folio_split support
When a zone device page is split (via huge pmd folio split). The
driver callback for folio_split is invoked to let the device driver
know that the folio size has been split into a smaller order.
The HMM test driver has been updated to handle the split, since the
test driver uses backing pages, it requires a mechanism of reorganizing
the backing pages (backing pages are used to create a mirror device)
again into the right sized order pages. This is supported by exporting
prep_compound_page().
Cc: Karol Herbst <kherbst@...hat.com>
Cc: Lyude Paul <lyude@...hat.com>
Cc: Danilo Krummrich <dakr@...nel.org>
Cc: David Airlie <airlied@...il.com>
Cc: Simona Vetter <simona@...ll.ch>
Cc: "Jérôme Glisse" <jglisse@...hat.com>
Cc: Shuah Khan <shuah@...nel.org>
Cc: David Hildenbrand <david@...hat.com>
Cc: Barry Song <baohua@...nel.org>
Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: Ryan Roberts <ryan.roberts@....com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Peter Xu <peterx@...hat.com>
Cc: Zi Yan <ziy@...dia.com>
Cc: Kefeng Wang <wangkefeng.wang@...wei.com>
Cc: Jane Chu <jane.chu@...cle.com>
Cc: Alistair Popple <apopple@...dia.com>
Cc: Donet Tom <donettom@...ux.ibm.com>
Signed-off-by: Balbir Singh <balbirs@...dia.com>
---
include/linux/memremap.h | 7 +++++++
include/linux/mm.h | 1 +
lib/test_hmm.c | 42 ++++++++++++++++++++++++++++++++++++++++
mm/huge_memory.c | 14 ++++++++++++++
mm/page_alloc.c | 1 +
5 files changed, 65 insertions(+)
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 11d586dd8ef1..2091b754f1da 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -100,6 +100,13 @@ struct dev_pagemap_ops {
*/
int (*memory_failure)(struct dev_pagemap *pgmap, unsigned long pfn,
unsigned long nr_pages, int mf_flags);
+
+ /*
+ * Used for private (un-addressable) device memory only.
+ * This callback is used when a folio is split into
+ * a smaller folio
+ */
+ void (*folio_split)(struct folio *head, struct folio *tail);
};
#define PGMAP_ALTMAP_VALID (1 << 0)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index ef40f68c1183..f7bda8b1e46c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1183,6 +1183,7 @@ static inline struct folio *virt_to_folio(const void *x)
void __folio_put(struct folio *folio);
void split_page(struct page *page, unsigned int order);
+void prep_compound_page(struct page *page, unsigned int order);
void folio_copy(struct folio *dst, struct folio *src);
int folio_mc_copy(struct folio *dst, struct folio *src);
diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index 95b4276a17fd..e20021fb7c69 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -1646,9 +1646,51 @@ static vm_fault_t dmirror_devmem_fault(struct vm_fault *vmf)
return ret;
}
+static void dmirror_devmem_folio_split(struct folio *head, struct folio *tail)
+{
+ struct page *rpage = BACKING_PAGE(folio_page(head, 0));
+ struct page *rpage_tail;
+ struct folio *rfolio;
+ unsigned long offset = 0;
+ unsigned int tail_order;
+ unsigned int head_order = folio_order(head);
+
+ if (!rpage) {
+ tail->page.zone_device_data = NULL;
+ return;
+ }
+
+ rfolio = page_folio(rpage);
+
+ if (tail == NULL) {
+ folio_reset_order(rfolio);
+ rfolio->mapping = NULL;
+ if (head_order)
+ prep_compound_page(rpage, head_order);
+ folio_set_count(rfolio, 1 << head_order);
+ return;
+ }
+
+ offset = folio_pfn(tail) - folio_pfn(head);
+
+ rpage_tail = folio_page(rfolio, offset);
+ tail->page.zone_device_data = rpage_tail;
+ clear_compound_head(rpage_tail);
+ rpage_tail->mapping = NULL;
+
+ tail_order = folio_order(tail);
+ if (tail_order)
+ prep_compound_page(rpage_tail, tail_order);
+
+ folio_page(tail, 0)->mapping = folio_page(head, 0)->mapping;
+ tail->pgmap = head->pgmap;
+ folio_set_count(page_folio(rpage_tail), 1 << tail_order);
+}
+
static const struct dev_pagemap_ops dmirror_devmem_ops = {
.page_free = dmirror_devmem_free,
.migrate_to_ram = dmirror_devmem_fault,
+ .folio_split = dmirror_devmem_folio_split,
};
static int dmirror_device_init(struct dmirror_device *mdevice, int id)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f29add796931..d55e36ae0c39 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3630,6 +3630,11 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
if (release == origin_folio)
continue;
+ if (folio_is_device_private(origin_folio) &&
+ origin_folio->pgmap->ops->folio_split)
+ origin_folio->pgmap->ops->folio_split(
+ origin_folio, release);
+
folio_ref_unfreeze(release, 1 +
((mapping || swap_cache) ?
folio_nr_pages(release) : 0));
@@ -3661,6 +3666,15 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
}
}
+ /*
+ * Mark the end of the split, so that the driver can setup origin_folio's
+ * order and other metadata
+ */
+ if (folio_is_device_private(origin_folio) &&
+ origin_folio->pgmap->ops->folio_split)
+ origin_folio->pgmap->ops->folio_split(
+ origin_folio, NULL);
+
/*
* Unfreeze origin_folio only after all page cache entries, which used
* to point to it, have been updated with new folios. Otherwise,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4f55f8ed65c7..0a538e9c24bd 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -722,6 +722,7 @@ void prep_compound_page(struct page *page, unsigned int order)
prep_compound_head(page, order);
}
+EXPORT_SYMBOL_GPL(prep_compound_page);
static inline void set_buddy_order(struct page *page, unsigned int order)
{
--
2.49.0
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