[PATCH 03/13] filemap: align the index to mapping_min_order in the page cache

[Pankaj Raghav (Samsung)]

From: Luis Chamberlain <mcgrof@xxxxxxxxxx>

Supporting mapping_min_order implies that we guarantee each folio in the
page cache has at least an order of mapping_min_order. So when adding new
folios to the page cache we must ensure the index used is aligned to the
mapping_min_order as the page cache requires the index to be aligned to
the order of the folio.

A higher order folio than min_order by definition is a multiple of the
min_order. If an index is aligned to an order higher than a min_order, it
will also be aligned to the min order.

This effectively introduces no new functional changes when min order is
not set other than a few rounding computations that should result in the
same value.

Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Signed-off-by: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
---
 include/linux/pagemap.h |  8 ++++++++
 mm/filemap.c            | 22 +++++++++++++---------
 2 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index fc8eb9c94e9c..fe8e1fbb667d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1328,6 +1328,14 @@ struct readahead_control {
 		._index = i,						\
 	}
 
+#define DEFINE_READAHEAD_ALIGNED(ractl, f, r, m, i)			\
+	struct readahead_control ractl = {				\
+		.file = f,						\
+		.mapping = m,						\
+		.ra = r,						\
+		._index = mapping_align_start_index(m, i),		\
+	}
+
 #define VM_READAHEAD_PAGES	(SZ_128K / PAGE_SIZE)
 
 void page_cache_ra_unbounded(struct readahead_control *,
diff --git a/mm/filemap.c b/mm/filemap.c
index 2b00442b9d19..bdf4f65f597c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2478,11 +2478,11 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count,
 	struct file *filp = iocb->ki_filp;
 	struct address_space *mapping = filp->f_mapping;
 	struct file_ra_state *ra = &filp->f_ra;
-	pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
-	pgoff_t last_index;
+	pgoff_t index, last_index;
 	struct folio *folio;
 	int err = 0;
 
+	index = mapping_align_start_index(mapping, iocb->ki_pos >> PAGE_SHIFT);
 	/* "last_index" is the index of the page beyond the end of the read */
 	last_index = DIV_ROUND_UP(iocb->ki_pos + count, PAGE_SIZE);
 retry:
@@ -2500,8 +2500,7 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count,
 	if (!folio_batch_count(fbatch)) {
 		if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))
 			return -EAGAIN;
-		err = filemap_create_folio(filp, mapping,
-				iocb->ki_pos >> PAGE_SHIFT, fbatch);
+		err = filemap_create_folio(filp, mapping, index, fbatch);
 		if (err == AOP_TRUNCATED_PAGE)
 			goto retry;
 		return err;
@@ -3093,7 +3092,7 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
 	struct file *file = vmf->vma->vm_file;
 	struct file_ra_state *ra = &file->f_ra;
 	struct address_space *mapping = file->f_mapping;
-	DEFINE_READAHEAD(ractl, file, ra, mapping, vmf->pgoff);
+	DEFINE_READAHEAD_ALIGNED(ractl, file, ra, mapping, vmf->pgoff);
 	struct file *fpin = NULL;
 	unsigned long vm_flags = vmf->vma->vm_flags;
 	unsigned int mmap_miss;
@@ -3147,7 +3146,7 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
 	ra->start = max_t(long, 0, vmf->pgoff - ra->ra_pages / 2);
 	ra->size = ra->ra_pages;
 	ra->async_size = ra->ra_pages / 4;
-	ractl._index = ra->start;
+	ractl._index = mapping_align_start_index(mapping, ra->start);
 	page_cache_ra_order(&ractl, ra, 0);
 	return fpin;
 }
@@ -3162,7 +3161,7 @@ static struct file *do_async_mmap_readahead(struct vm_fault *vmf,
 {
 	struct file *file = vmf->vma->vm_file;
 	struct file_ra_state *ra = &file->f_ra;
-	DEFINE_READAHEAD(ractl, file, ra, file->f_mapping, vmf->pgoff);
+	DEFINE_READAHEAD_ALIGNED(ractl, file, ra, file->f_mapping, vmf->pgoff);
 	struct file *fpin = NULL;
 	unsigned int mmap_miss;
 
@@ -3211,11 +3210,12 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
 	struct file *fpin = NULL;
 	struct address_space *mapping = file->f_mapping;
 	struct inode *inode = mapping->host;
-	pgoff_t max_idx, index = vmf->pgoff;
+	pgoff_t max_idx, index;
 	struct folio *folio;
 	vm_fault_t ret = 0;
 	bool mapping_locked = false;
 
+	index = mapping_align_start_index(mapping, vmf->pgoff);
 	max_idx = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
 	if (unlikely(index >= max_idx))
 		return VM_FAULT_SIGBUS;
@@ -3321,7 +3321,10 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
 		return VM_FAULT_SIGBUS;
 	}
 
-	vmf->page = folio_file_page(folio, index);
+	VM_BUG_ON_FOLIO(folio_order(folio) < mapping_min_folio_order(mapping),
+			folio);
+
+	vmf->page = folio_file_page(folio, vmf->pgoff);
 	return ret | VM_FAULT_LOCKED;
 
 page_not_uptodate:
@@ -3657,6 +3660,7 @@ static struct folio *do_read_cache_folio(struct address_space *mapping,
 	struct folio *folio;
 	int err;
 
+	index = mapping_align_start_index(mapping, index);
 	if (!filler)
 		filler = mapping->a_ops->read_folio;
 repeat:
-- 
2.43.0