[RFC,08/23] filemap: align the index to mapping_min_order in filemap_get_folios_tag()

Commit Message

Pankaj Raghav (Samsung) Sept. 15, 2023, 6:38 p.m. UTC

From: Luis Chamberlain <[e-mail]>

Align the index to the mapping_min_order number of pages while setting
the XA_STATE in filemap_get_folios_tag().

Signed-off-by: Luis Chamberlain <[e-mail]>
---
 mm/filemap.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Comments

Matthew Wilcox Sept. 15, 2023, 7:50 p.m. UTC | #1

On Fri, Sep 15, 2023 at 08:38:33PM +0200, Pankaj Raghav wrote:
> From: Luis Chamberlain <[e-mail]>
> 
> Align the index to the mapping_min_order number of pages while setting
> the XA_STATE in filemap_get_folios_tag().

... because?  It should already search backwards in the page cache,
otherwise calling sync_file_range() would skip the start if it landed
in a tail page of a folio.

Luis Chamberlain Sept. 18, 2023, 6:36 p.m. UTC | #2

On Fri, Sep 15, 2023 at 08:50:59PM +0100, Matthew Wilcox wrote:
> On Fri, Sep 15, 2023 at 08:38:33PM +0200, Pankaj Raghav wrote:
> > From: Luis Chamberlain <[e-mail]>
> > 
> > Align the index to the mapping_min_order number of pages while setting
> > the XA_STATE in filemap_get_folios_tag().
> 
> ... because?  It should already search backwards in the page cache,
> otherwise calling sync_file_range() would skip the start if it landed
> in a tail page of a folio.

Thanks! Will drop and verify!

  Luis

Patch

diff --git a/mm/filemap.c b/mm/filemap.c
index 15bc810bfc89..21e1341526ab 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2280,7 +2280,9 @@  EXPORT_SYMBOL(filemap_get_folios_contig);
 unsigned filemap_get_folios_tag(struct address_space *mapping, pgoff_t *start,
 			pgoff_t end, xa_mark_t tag, struct folio_batch *fbatch)
 {
-	XA_STATE(xas, &mapping->i_pages, *start);
+	unsigned int min_order = mapping_min_folio_order(mapping);
+	unsigned int nrpages = 1UL << min_order;
+	XA_STATE(xas, &mapping->i_pages, round_down(*start, nrpages));
 	struct folio *folio;
 
 	rcu_read_lock();