[RFC v2 02/14] filemap: align the index to mapping_min_order in the page cache

["Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>]

From: Luis Chamberlain <mcgrof@kernel.org>

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@kernel.org>
Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
---
 mm/filemap.c | 34 ++++++++++++++++++++++++++--------
 1 file changed, 26 insertions(+), 8 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 750e779c23db..323a8e169581 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2479,14 +2479,16 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count,
 {
 	struct file *filp = iocb->ki_filp;
 	struct address_space *mapping = filp->f_mapping;
+	unsigned int min_nrpages = mapping_min_folio_nrpages(mapping);
 	struct file_ra_state *ra = &filp->f_ra;
-	pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
+	pgoff_t index = round_down(iocb->ki_pos >> PAGE_SHIFT, min_nrpages);
 	pgoff_t last_index;
 	struct folio *folio;
 	int err = 0;
 
 	/* "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);
+	last_index = round_up(last_index, min_nrpages);
 retry:
 	if (fatal_signal_pending(current))
 		return -EINTR;
@@ -2502,8 +2504,7 @@ 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;
@@ -3095,7 +3096,10 @@ 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);
+	unsigned int min_order = mapping_min_folio_order(mapping);
+	unsigned int min_nrpages = mapping_min_folio_nrpages(file->f_mapping);
+	pgoff_t index = round_down(vmf->pgoff, min_nrpages);
+	DEFINE_READAHEAD(ractl, file, ra, mapping, index);
 	struct file *fpin = NULL;
 	unsigned long vm_flags = vmf->vma->vm_flags;
 	unsigned int mmap_miss;
@@ -3147,10 +3151,11 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
 	 */
 	fpin = maybe_unlock_mmap_for_io(vmf, fpin);
 	ra->start = max_t(long, 0, vmf->pgoff - ra->ra_pages / 2);
+	ra->start = round_down(ra->start, min_nrpages);
 	ra->size = ra->ra_pages;
 	ra->async_size = ra->ra_pages / 4;
 	ractl._index = ra->start;
-	page_cache_ra_order(&ractl, ra, 0);
+	page_cache_ra_order(&ractl, ra, min_order);
 	return fpin;
 }
 
@@ -3164,7 +3169,9 @@ 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);
+	unsigned int min_nrpages = mapping_min_folio_nrpages(file->f_mapping);
+	pgoff_t index = round_down(vmf->pgoff, min_nrpages);
+	DEFINE_READAHEAD(ractl, file, ra, file->f_mapping, index);
 	struct file *fpin = NULL;
 	unsigned int mmap_miss;
 
@@ -3212,13 +3219,17 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
 	struct file *file = vmf->vma->vm_file;
 	struct file *fpin = NULL;
 	struct address_space *mapping = file->f_mapping;
+	unsigned int min_order = mapping_min_folio_order(mapping);
+	unsigned int nrpages = 1UL << min_order;
 	struct inode *inode = mapping->host;
-	pgoff_t max_idx, index = vmf->pgoff;
+	pgoff_t max_idx, index = round_down(vmf->pgoff, nrpages);
 	struct folio *folio;
 	vm_fault_t ret = 0;
 	bool mapping_locked = false;
 
 	max_idx = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
+	max_idx = round_up(max_idx, nrpages);
+
 	if (unlikely(index >= max_idx))
 		return VM_FAULT_SIGBUS;
 
@@ -3317,13 +3328,17 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
 	 * We must recheck i_size under page lock.
 	 */
 	max_idx = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
+	max_idx = round_up(max_idx, nrpages);
+
 	if (unlikely(index >= max_idx)) {
 		folio_unlock(folio);
 		folio_put(folio);
 		return VM_FAULT_SIGBUS;
 	}
 
-	vmf->page = folio_file_page(folio, index);
+	VM_BUG_ON_FOLIO(folio_order(folio) < min_order, folio);
+
+	vmf->page = folio_file_page(folio, vmf->pgoff);
 	return ret | VM_FAULT_LOCKED;
 
 page_not_uptodate:
@@ -3658,6 +3673,9 @@ static struct folio *do_read_cache_folio(struct address_space *mapping,
 {
 	struct folio *folio;
 	int err;
+	unsigned int min_nrpages = mapping_min_folio_nrpages(mapping);
+
+	index = round_down(index, min_nrpages);
 
 	if (!filler)
 		filler = mapping->a_ops->read_folio;
-- 
2.43.0