[PATCH 12/12] shmem: add large folio support to the write and fallocate paths

[Daniel Gomez <da.gomez@xxxxxxxxxxx>]

Add large folio support for shmem write and fallocate paths matching the
same high order preference mechanism used in the iomap buffered IO path
as used in __filemap_get_folio().

Add shmem_mapping_size_order() to get a hint for the order of the folio
based on the file size which takes care of the mapping requirements.

Swap does not support high order folios for now, so make it order-0 in
case swap is enabled.

Skip high order folio allocation loop when reclaim path returns with no
space left (ENOSPC).

Add __GFP_COMP flag for high order folios allocation path to fix a
memory leak.

Signed-off-by: Daniel Gomez <da.gomez@xxxxxxxxxxx>
---
 mm/shmem.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 47 insertions(+), 2 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index fcd2c9befe19..9308a334a940 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1836,23 +1836,63 @@ static struct folio *shmem_alloc_folio(gfp_t gfp, struct shmem_inode_info *info,
 	struct page *page;
 
 	mpol = shmem_get_pgoff_policy(info, index, order, &ilx);
-	page = alloc_pages_mpol(gfp, order, mpol, ilx, numa_node_id());
+	page = alloc_pages_mpol(gfp | __GFP_COMP, order, mpol, ilx,
+				numa_node_id());
 	mpol_cond_put(mpol);
 
 	return page_rmappable_folio(page);
 }
 
+/**
+ * shmem_mapping_size_order - Get maximum folio order for the given file size.
+ * @mapping: Target address_space.
+ * @index: The page index.
+ * @size: The suggested size of the folio to create.
+ *
+ * This returns a high order for folios (when supported) based on the file size
+ * which the mapping currently allows at the given index. The index is relevant
+ * due to alignment considerations the mapping might have. The returned order
+ * may be less than the size passed.
+ *
+ * Like __filemap_get_folio order calculation.
+ *
+ * Return: The order.
+ */
+static inline unsigned int
+shmem_mapping_size_order(struct address_space *mapping, pgoff_t index,
+			 size_t size, struct shmem_sb_info *sbinfo)
+{
+	unsigned int order = ilog2(size);
+
+	if ((order <= PAGE_SHIFT) ||
+	    (!mapping_large_folio_support(mapping) || !sbinfo->noswap))
+		return 0;
+
+	order -= PAGE_SHIFT;
+
+	/* If we're not aligned, allocate a smaller folio */
+	if (index & ((1UL << order) - 1))
+		order = __ffs(index);
+
+	order = min_t(size_t, order, MAX_PAGECACHE_ORDER);
+
+	/* Order-1 not supported due to THP dependency */
+	return (order == 1) ? 0 : order;
+}
+
 static struct folio *shmem_alloc_and_add_folio(gfp_t gfp,
 		struct inode *inode, pgoff_t index,
 		struct mm_struct *fault_mm, bool huge, size_t len)
 {
 	struct address_space *mapping = inode->i_mapping;
 	struct shmem_inode_info *info = SHMEM_I(inode);
-	unsigned int order = 0;
+	unsigned int order = shmem_mapping_size_order(mapping, index, len,
+						      SHMEM_SB(inode->i_sb));
 	struct folio *folio;
 	long pages;
 	int error;
 
+neworder:
 	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
 		huge = false;
 
@@ -1937,6 +1977,11 @@ static struct folio *shmem_alloc_and_add_folio(gfp_t gfp,
 unlock:
 	folio_unlock(folio);
 	folio_put(folio);
+	if ((error != -ENOSPC) && (order > 0)) {
+		if (--order == 1)
+			order = 0;
+		goto neworder;
+	}
 	return ERR_PTR(error);
 }
 
-- 
2.43.0