[PATCH v7 3/6] mm/gup: Introduce memfd_pin_folios() for pinning memfd folios (v7)
Vivek Kasireddy
vivek.kasireddy at intel.com
Tue Dec 12 07:38:00 UTC 2023
For drivers that would like to longterm-pin the folios associated
with a memfd, the memfd_pin_folios() API provides an option to
not only pin the folios via FOLL_PIN but also to check and migrate
them if they reside in movable zone or CMA block. This API
currently works with memfds but it should work with any files
that belong to either shmemfs or hugetlbfs. Files belonging to
other filesystems are rejected for now.
The folios need to be located first before pinning them via FOLL_PIN.
If they are found in the page cache, they can be immediately pinned.
Otherwise, they need to be allocated using the filesystem specific
APIs and then pinned.
v2:
- Drop gup_flags and improve comments and commit message (David)
- Allocate a page if we cannot find in page cache for the hugetlbfs
case as well (David)
- Don't unpin pages if there is a migration related failure (David)
- Drop the unnecessary nr_pages <= 0 check (Jason)
- Have the caller of the API pass in file * instead of fd (Jason)
v3: (David)
- Enclose the huge page allocation code with #ifdef CONFIG_HUGETLB_PAGE
(Build error reported by kernel test robot <lkp at intel.com>)
- Don't forget memalloc_pin_restore() on non-migration related errors
- Improve the readability of the cleanup code associated with
non-migration related errors
- Augment the comments by describing FOLL_LONGTERM like behavior
- Include the R-b tag from Jason
v4:
- Remove the local variable "page" and instead use 3 return statements
in alloc_file_page() (David)
- Add the R-b tag from David
v5: (David)
- For hugetlb case, ensure that we only obtain head pages from the
mapping by using __filemap_get_folio() instead of find_get_page_flags()
- Handle -EEXIST when two or more potential users try to simultaneously
add a huge page to the mapping by forcing them to retry on failure
v6: (Christoph)
- Rename this API to memfd_pin_user_pages() to make it clear that it
is intended for memfds
- Move the memfd page allocation helper from gup.c to memfd.c
- Fix indentation errors in memfd_pin_user_pages()
- For contiguous ranges of folios, use a helper such as
filemap_get_folios_contig() to lookup the page cache in batches
v7:
- Rename this API to memfd_pin_folios() and make it return folios
and offsets instead of pages (David)
- Don't continue processing the folios in the batch returned by
filemap_get_folios_contig() if they do not have correct next_idx
- Add the R-b tag from Christoph
Cc: David Hildenbrand <david at redhat.com>
Cc: Christoph Hellwig <hch at infradead.org>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Mike Kravetz <mike.kravetz at oracle.com>
Cc: Hugh Dickins <hughd at google.com>
Cc: Peter Xu <peterx at redhat.com>
Cc: Gerd Hoffmann <kraxel at redhat.com>
Cc: Dongwon Kim <dongwon.kim at intel.com>
Cc: Junxiao Chang <junxiao.chang at intel.com>
Suggested-by: Jason Gunthorpe <jgg at nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg at nvidia.com> (v2)
Reviewed-by: David Hildenbrand <david at redhat.com> (v3)
Reviewed-by: Christoph Hellwig <hch at lst.de> (v6)
Signed-off-by: Vivek Kasireddy <vivek.kasireddy at intel.com>
---
include/linux/memfd.h | 5 ++
include/linux/mm.h | 3 +
mm/gup.c | 155 ++++++++++++++++++++++++++++++++++++++++++
mm/memfd.c | 34 +++++++++
4 files changed, 197 insertions(+)
diff --git a/include/linux/memfd.h b/include/linux/memfd.h
index e7abf6fa4c52..b38fb35f4271 100644
--- a/include/linux/memfd.h
+++ b/include/linux/memfd.h
@@ -6,11 +6,16 @@
#ifdef CONFIG_MEMFD_CREATE
extern long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int arg);
+extern struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx);
#else
static inline long memfd_fcntl(struct file *f, unsigned int c, unsigned int a)
{
return -EINVAL;
}
+static inline struct page *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
+{
+ return ERR_PTR(-EINVAL);
+}
#endif
#endif /* __LINUX_MEMFD_H */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 418d26608ece..537f40989837 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2472,6 +2472,9 @@ long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
struct page **pages, unsigned int gup_flags);
long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
struct page **pages, unsigned int gup_flags);
+long memfd_pin_folios(struct file *file, unsigned long start,
+ unsigned long nr_pages, struct folio **folios,
+ pgoff_t *offsets);
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 231711efa390..e798cdbc6a11 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -5,6 +5,7 @@
#include <linux/spinlock.h>
#include <linux/mm.h>
+#include <linux/memfd.h>
#include <linux/memremap.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
@@ -17,6 +18,7 @@
#include <linux/hugetlb.h>
#include <linux/migrate.h>
#include <linux/mm_inline.h>
+#include <linux/pagevec.h>
#include <linux/sched/mm.h>
#include <linux/shmem_fs.h>
@@ -3410,3 +3412,156 @@ long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
&locked, gup_flags);
}
EXPORT_SYMBOL(pin_user_pages_unlocked);
+
+/**
+ * memfd_pin_folios() - pin folios associated with a memfd
+ * @memfd: the memfd whose folios are to be pinned
+ * @start: starting memfd offset
+ * @nr_pages: number of pages from start to pin
+ * @folios: array that receives pointers to the folios pinned.
+ * Should be at-least nr_pages long.
+ * @offsets: array that receives offsets of pages in their folios.
+ * Should be at-least nr_pages long.
+ *
+ * Attempt to pin folios associated with a memfd; given that a memfd is
+ * either backed by shmem or hugetlb, the folios can either be found in
+ * the page cache or need to be allocated if necessary. Once the folios
+ * are located, they are all pinned via FOLL_PIN and the @offsets array
+ * is populated with offsets of the pages in their respective folios.
+ * Therefore, for each page the caller requested, there will be a
+ * corresponding entry in both @folios and @offsets. And, eventually,
+ * these pinned folios need to be released either using unpin_user_pages()
+ * or unpin_user_page().
+ *
+ * It must be noted that the folios may be pinned for an indefinite amount
+ * of time. And, in most cases, the duration of time they may stay pinned
+ * would be controlled by the userspace. This behavior is effectively the
+ * same as using FOLL_LONGTERM with other GUP APIs.
+ *
+ * Returns number of folios pinned. This would be equal to the number of
+ * pages requested. If no folios were pinned, it returns -errno.
+ */
+long memfd_pin_folios(struct file *memfd, unsigned long start,
+ unsigned long nr_pages, struct folio **folios,
+ pgoff_t *offsets)
+{
+ unsigned long end = start + (nr_pages << PAGE_SHIFT) - 1;
+ unsigned int max_pgs, pgoff, pgshift = PAGE_SHIFT;
+ pgoff_t start_idx, end_idx, next_idx;
+ unsigned int flags, nr_folios, i, j;
+ struct folio *folio = NULL;
+ struct folio_batch fbatch;
+ struct page **pages;
+ struct hstate *h;
+ long ret;
+
+ if (!nr_pages)
+ return -EINVAL;
+
+ if (!memfd)
+ return -EINVAL;
+
+ if (!shmem_file(memfd) && !is_file_hugepages(memfd))
+ return -EINVAL;
+
+ pages = kmalloc_array(nr_pages, sizeof(*pages), GFP_KERNEL);
+ if (!pages)
+ return -ENOMEM;
+
+ if (is_file_hugepages(memfd)) {
+ h = hstate_file(memfd);
+ pgshift = huge_page_shift(h);
+ }
+
+ flags = memalloc_pin_save();
+ do {
+ i = 0;
+ start_idx = start >> pgshift;
+ end_idx = end >> pgshift;
+ if (is_file_hugepages(memfd)) {
+ start_idx <<= huge_page_order(h);
+ end_idx <<= huge_page_order(h);
+ }
+
+ folio_batch_init(&fbatch);
+ while (start_idx <= end_idx) {
+ /*
+ * In most cases, we should be able to find the folios
+ * in the page cache. If we cannot find them for some
+ * reason, we try to allocate them and add them to the
+ * page cache.
+ */
+ nr_folios = filemap_get_folios_contig(memfd->f_mapping,
+ &start_idx,
+ end_idx,
+ &fbatch);
+ if (folio) {
+ folio_put(folio);
+ folio = NULL;
+ }
+
+ next_idx = 0;
+ for (j = 0; j < nr_folios; j++) {
+ if (next_idx &&
+ next_idx != folio_index(fbatch.folios[j]))
+ continue;
+
+ folio = try_grab_folio(&fbatch.folios[j]->page,
+ 1, FOLL_PIN);
+ if (!folio) {
+ folio_batch_release(&fbatch);
+ kfree(pages);
+ goto err;
+ }
+
+ max_pgs = folio_nr_pages(folio);
+ if (i == 0) {
+ pgoff = offset_in_folio(folio, start);
+ pgoff >>= PAGE_SHIFT;
+ }
+
+ do {
+ folios[i] = folio;
+ offsets[i] = pgoff << PAGE_SHIFT;
+ pages[i] = folio_page(folio, 0);
+ folio_add_pin(folio);
+
+ pgoff++;
+ i++;
+ } while (pgoff < max_pgs && i < nr_pages);
+
+ pgoff = 0;
+ next_idx = folio_next_index(folio);
+ gup_put_folio(folio, 1, FOLL_PIN);
+ }
+
+ folio = NULL;
+ folio_batch_release(&fbatch);
+ if (!nr_folios) {
+ folio = memfd_alloc_folio(memfd, start_idx);
+ if (IS_ERR(folio)) {
+ ret = PTR_ERR(folio);
+ if (ret != -EEXIST) {
+ kfree(pages);
+ goto err;
+ }
+ }
+ }
+ }
+
+ ret = check_and_migrate_movable_pages(nr_pages, pages);
+ } while (ret == -EAGAIN);
+
+ kfree(pages);
+ memalloc_pin_restore(flags);
+ return ret ? ret : nr_pages;
+err:
+ memalloc_pin_restore(flags);
+ while (i-- > 0)
+ if (folios[i])
+ gup_put_folio(folios[i], 1, FOLL_PIN);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(memfd_pin_folios);
+
diff --git a/mm/memfd.c b/mm/memfd.c
index d3a1ba4208c9..36a75e8249f8 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -63,6 +63,40 @@ static void memfd_tag_pins(struct xa_state *xas)
xas_unlock_irq(xas);
}
+/*
+ * This is a helper function used by memfd_pin_user_pages() in GUP (gup.c).
+ * It is mainly called to allocate a page in a memfd when the caller
+ * (memfd_pin_user_pages()) cannot find a page in the page cache at a given
+ * index in the mapping.
+ */
+struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
+{
+#ifdef CONFIG_HUGETLB_PAGE
+ struct folio *folio;
+ int err;
+
+ if (is_file_hugepages(memfd)) {
+ folio = alloc_hugetlb_folio_nodemask(hstate_file(memfd),
+ NUMA_NO_NODE,
+ NULL,
+ GFP_USER);
+ if (folio && folio_try_get(folio)) {
+ err = hugetlb_add_to_page_cache(folio,
+ memfd->f_mapping,
+ idx);
+ if (err) {
+ folio_put(folio);
+ free_huge_folio(folio);
+ return ERR_PTR(err);
+ }
+ return folio;
+ }
+ return ERR_PTR(-ENOMEM);
+ }
+#endif
+ return shmem_read_folio(memfd->f_mapping, idx);
+}
+
/*
* Setting SEAL_WRITE requires us to verify there's no pending writer. However,
* via get_user_pages(), drivers might have some pending I/O without any active
--
2.39.2
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