On 06.03.25 05:42, Balbir Singh wrote:
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().
Signed-off-by: Balbir Singh <balb...@nvidia.com>
---
include/linux/memremap.h | 7 +++++++
include/linux/mm.h | 1 +
lib/test_hmm.c | 35 +++++++++++++++++++++++++++++++++++
mm/huge_memory.c | 5 +++++
mm/page_alloc.c | 1 +
5 files changed, 49 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
Confusing. When a folio is split, it is split into multiple folios.
So when will this be invoked?
+ */
+ void (*folio_split)(struct folio *head, struct folio *tail);
head and tail are really suboptimal termonology. They refer to head and
tail pages, which is not really the case with folios (in the long run).
};
#define PGMAP_ALTMAP_VALID (1 << 0)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 98a67488b5fe..3d0e91e0a923 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1415,6 +1415,7 @@ 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 a81d2f8a0426..18b6a7b061d7 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -1640,10 +1640,45 @@ 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 folio *new_rfolio;
+ struct folio *rfolio;
+ unsigned long offset = 0;
+
+ if (!rpage) {
+ folio_page(tail, 0)->zone_device_data = NULL;
+ return;
+ }
+
+ offset = folio_pfn(tail) - folio_pfn(head);
+ rfolio = page_folio(rpage);
+ new_rfolio = page_folio(folio_page(rfolio, offset));
+
+ folio_page(tail, 0)->zone_device_data = folio_page(new_rfolio, 0);
+
+ if (folio_pfn(tail) - folio_pfn(head) == 1) {
+ if (folio_order(head))
+ prep_compound_page(folio_page(rfolio, 0),
+ folio_order(head));
+ folio_set_count(rfolio, 1);
+ }
+ clear_compound_head(folio_page(new_rfolio, 0));
+ if (folio_order(tail))
+ prep_compound_page(folio_page(new_rfolio, 0),
+ folio_order(tail));
+ folio_set_count(new_rfolio, 1);
+ folio_page(new_rfolio, 0)->mapping = folio_page(rfolio, 0)->mapping;
+ tail->pgmap = head->pgmap;
Most of this doesn't look like it should be the responsibility of this
callback.
Setting up a new folio after the split (messing with compound pages etc)
really should not be the responsibility of this callback.
So no, this looks misplaced.
+}
+
static const struct dev_pagemap_ops dmirror_devmem_ops = {
.page_free = dmirror_devmem_free,
.migrate_to_ram = dmirror_devmem_fault,
.page_free = dmirror_devmem_free,
+ .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 995ac8be5709..518a70d1b58a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3655,6 +3655,11 @@ static int __split_unmapped_folio(struct folio *folio,
int new_order,
MTHP_STAT_NR_ANON, 1);
}
+ if (folio_is_device_private(origin_folio) &&
+ origin_folio->pgmap->ops->folio_split)
+ origin_folio->pgmap->ops->folio_split(
+ origin_folio, release);
Absolutely ugly. I think we need a wrapper for the
+
/*
* Unfreeze refcount first. Additional reference from
* page cache.
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 17ea8fb27cbf..563f7e39aa79 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -573,6 +573,7 @@ void prep_compound_page(struct page *page, unsigned int
order)
prep_compound_head(page, order);
}
+EXPORT_SYMBOL_GPL(prep_compound_page);
Hmmm, that is questionable. We don't want arbitrary modules to make use
of that.
Another sign that you are exposing the wrong functionality/interface
(folio_split) to modules.
--
Cheers,
David / dhildenb
