On 9/17/2024 8:25 AM, David Hildenbrand wrote:
On 14.09.24 15:19, Steven Sistare wrote:
cc'ing linux-mm for review of this one patch of the series.
This proposes a new KAPI function repin_folio_unhugely(), for use in this
patch of the iommu_ioas_map_file series:
iommufd: IOMMU_IOAS_MAP_FILE implementation
https://lore.kernel.org/linux-iommu/1726319158-283074-7-git-send-email-steven.sistare@xxxxxxxxxx
- Steve
On 9/14/2024 9:05 AM, Steve Sistare wrote:
Export a function that repins a huge-page folio at small-page granularity.
This allows any range of small pages within the folio to be unpinned later.
For example, pages pinned via memfd_pin_folios and modified by
repin_folio_unhugely could be unpinned via unpin_user_page(s).
Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Steve Sistare <steven.sistare@xxxxxxxxxx>
---
include/linux/mm.h | 1 +
mm/gup.c | 18 ++++++++++++++++++
2 files changed, 19 insertions(+)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1470736..ba8344f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2514,6 +2514,7 @@ long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end,
struct folio **folios, unsigned int max_folios,
pgoff_t *offset);
+void repin_folio_unhugely(struct folio *folio, unsigned long npin);
int get_user_pages_fast(unsigned long start, int nr_pages,
unsigned int gup_flags, struct page **pages);
diff --git a/mm/gup.c b/mm/gup.c
index 947881ff..f8f3f2a 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -3720,3 +3720,21 @@ long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end,
return ret;
}
EXPORT_SYMBOL_GPL(memfd_pin_folios);
+
+/**
+ * repin_folio_unhugely() - repin a folio at small page granularity
+ * @folio: the folio to repin
+ * @npin: the number of pages pinned in the folio
+ *
+ * Given a huge page folio that is already pinned, and the number of small
s/huge page folio/large folio/
+ * pages that are pinned in it, adjust the pincount to reflect small-page
+ * granularity. Each small page can later be unpinned individually.
+ */
+void repin_folio_unhugely(struct folio *folio, unsigned long npin)
+{
+ if (!folio_test_large(folio) || is_huge_zero_folio(folio) || npin == 1)
Why not the huge zero folio? That looks very odd here.
The zero page is treated specially here and elsewhere, it can never be deleted so
reference fiddling is skipped.
+ return;
+ atomic_add(npin - 1, &folio->_refcount);
+ atomic_add(npin - 1, &folio->_pincount);
+}
+EXPORT_SYMBOL_GPL(repin_folio_unhugely);
Can we ... find a better name? For example, it's "large" folio not "huge"...
And repin is really misleading. We are simply adding more pins to an already pinned one ...
Jason suggests a better name in the other thread.
- Steve
