diff mbox series

[04/13] filemap: use mapping_min_order while allocating folios

Message ID 20240226094936.2677493-5-kernel@pankajraghav.com (mailing list archive)
State New
Headers show
Series enable bs > ps in XFS | expand

Commit Message

Pankaj Raghav (Samsung) Feb. 26, 2024, 9:49 a.m. UTC 
From: Pankaj Raghav <p.raghav@samsung.com>

filemap_create_folio() and do_read_cache_folio() were always allocating
folio of order 0. __filemap_get_folio was trying to allocate higher
order folios when fgp_flags had higher order hint set but it will default
to order 0 folio if higher order memory allocation fails.

As we bring the notion of mapping_min_order, make sure these functions
allocate at least folio of mapping_min_order as we need to guarantee it
in the page cache.

Add some additional VM_BUG_ON() in page_cache_delete[batch] and
__filemap_add_folio to catch errors where we delete or add folios that
has order less than min_order.

Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Acked-by: Darrick J. Wong <djwong@kernel.org>
---
 mm/filemap.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

Comments

Matthew Wilcox Feb. 26, 2024, 2:47 p.m. UTC | #1 
On Mon, Feb 26, 2024 at 10:49:27AM +0100, Pankaj Raghav (Samsung) wrote:
> Add some additional VM_BUG_ON() in page_cache_delete[batch] and
> __filemap_add_folio to catch errors where we delete or add folios that
> has order less than min_order.

I don't understand why we need these checks in the deletion path.  The
add path, yes, absolutely.  But the delete path?

> @@ -896,6 +900,8 @@ noinline int __filemap_add_folio(struct address_space *mapping,
>  			}
>  		}
>  
> +		VM_BUG_ON_FOLIO(folio_order(folio) < mapping_min_folio_order(mapping),
> +				folio);

But I don't understand why you put it here, while we're holding the
xa_lock.  That seems designed to cause maximum disruption.  Why not put
it at the beginning of the function with all the other VM_BUG_ON_FOLIO?

> @@ -1847,6 +1853,9 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
>  		fgf_t fgp_flags, gfp_t gfp)
>  {
>  	struct folio *folio;
> +	unsigned int min_order = mapping_min_folio_order(mapping);
> +
> +	index = mapping_align_start_index(mapping, index);

I would not do this here.

>  repeat:
>  	folio = filemap_get_entry(mapping, index);
> @@ -1886,7 +1895,7 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
>  		folio_wait_stable(folio);
>  no_page:
>  	if (!folio && (fgp_flags & FGP_CREAT)) {
> -		unsigned order = FGF_GET_ORDER(fgp_flags);
> +		unsigned int order = max(min_order, FGF_GET_ORDER(fgp_flags));
>  		int err;

Put it here instead.

>  		if ((fgp_flags & FGP_WRITE) && mapping_can_writeback(mapping))
> @@ -1912,8 +1921,13 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
>  			gfp_t alloc_gfp = gfp;
>  
>  			err = -ENOMEM;
> +			if (order < min_order)
> +				order = min_order;
>  			if (order > 0)
>  				alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN;
> +
> +			VM_BUG_ON(index & ((1UL << order) - 1));

Then you don't need this BUG_ON because it's obvious you just did it.
And the one in filemap_add_folio() would catch it anyway.
Pankaj Raghav (Samsung) Feb. 27, 2024, 12:09 p.m. UTC | #2 
On Mon, Feb 26, 2024 at 02:47:33PM +0000, Matthew Wilcox wrote:
> On Mon, Feb 26, 2024 at 10:49:27AM +0100, Pankaj Raghav (Samsung) wrote:
> > Add some additional VM_BUG_ON() in page_cache_delete[batch] and
> > __filemap_add_folio to catch errors where we delete or add folios that
> > has order less than min_order.
> 
> I don't understand why we need these checks in the deletion path.  The
> add path, yes, absolutely.  But the delete path?
I think we initially added it to check if some split happened which
might mess up the page cache with min order support. But I think it is
not super critical anymore because of the changes in the split_folio
path. I will remove the checks.

> 
> > @@ -896,6 +900,8 @@ noinline int __filemap_add_folio(struct address_space *mapping,
> >  			}
> >  		}
> >  
> > +		VM_BUG_ON_FOLIO(folio_order(folio) < mapping_min_folio_order(mapping),
> > +				folio);
> 
> But I don't understand why you put it here, while we're holding the
> xa_lock.  That seems designed to cause maximum disruption.  Why not put
> it at the beginning of the function with all the other VM_BUG_ON_FOLIO?

Yeah. That makes sense as the folio itself is not changing.

> 
> > @@ -1847,6 +1853,9 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
> >  		fgf_t fgp_flags, gfp_t gfp)
> >  {
> >  	struct folio *folio;
> > +	unsigned int min_order = mapping_min_folio_order(mapping);
> > +
> > +	index = mapping_align_start_index(mapping, index);
> 
> I would not do this here.
> 
> >  repeat:
> >  	folio = filemap_get_entry(mapping, index);
> > @@ -1886,7 +1895,7 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
> >  		folio_wait_stable(folio);
> >  no_page:
> >  	if (!folio && (fgp_flags & FGP_CREAT)) {
> > -		unsigned order = FGF_GET_ORDER(fgp_flags);
> > +		unsigned int order = max(min_order, FGF_GET_ORDER(fgp_flags));
> >  		int err;
> 
> Put it here instead.
> 
> >  		if ((fgp_flags & FGP_WRITE) && mapping_can_writeback(mapping))
> > @@ -1912,8 +1921,13 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
> >  			gfp_t alloc_gfp = gfp;
> >  
> >  			err = -ENOMEM;
> > +			if (order < min_order)
> > +				order = min_order;
> >  			if (order > 0)
> >  				alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN;
> > +
> > +			VM_BUG_ON(index & ((1UL << order) - 1));
> 
> Then you don't need this BUG_ON because it's obvious you just did it.
> And the one in filemap_add_folio() would catch it anyway.

I agree. I will change it in the next revision.
diff mbox series

Patch

diff --git a/mm/filemap.c b/mm/filemap.c
index bdf4f65f597c..4b144479c4cb 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -135,6 +135,8 @@  static void page_cache_delete(struct address_space *mapping,
 	xas_set_order(&xas, folio->index, folio_order(folio));
 	nr = folio_nr_pages(folio);
 
+	VM_BUG_ON_FOLIO(folio_order(folio) < mapping_min_folio_order(mapping),
+			folio);
 	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
 
 	xas_store(&xas, shadow);
@@ -305,6 +307,8 @@  static void page_cache_delete_batch(struct address_space *mapping,
 
 		WARN_ON_ONCE(!folio_test_locked(folio));
 
+		VM_BUG_ON_FOLIO(folio_order(folio) < mapping_min_folio_order(mapping),
+				folio);
 		folio->mapping = NULL;
 		/* Leave folio->index set: truncation lookup relies on it */
 
@@ -896,6 +900,8 @@  noinline int __filemap_add_folio(struct address_space *mapping,
 			}
 		}
 
+		VM_BUG_ON_FOLIO(folio_order(folio) < mapping_min_folio_order(mapping),
+				folio);
 		xas_store(&xas, folio);
 		if (xas_error(&xas))
 			goto unlock;
@@ -1847,6 +1853,9 @@  struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 		fgf_t fgp_flags, gfp_t gfp)
 {
 	struct folio *folio;
+	unsigned int min_order = mapping_min_folio_order(mapping);
+
+	index = mapping_align_start_index(mapping, index);
 
 repeat:
 	folio = filemap_get_entry(mapping, index);
@@ -1886,7 +1895,7 @@  struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 		folio_wait_stable(folio);
 no_page:
 	if (!folio && (fgp_flags & FGP_CREAT)) {
-		unsigned order = FGF_GET_ORDER(fgp_flags);
+		unsigned int order = max(min_order, FGF_GET_ORDER(fgp_flags));
 		int err;
 
 		if ((fgp_flags & FGP_WRITE) && mapping_can_writeback(mapping))
@@ -1912,8 +1921,13 @@  struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 			gfp_t alloc_gfp = gfp;
 
 			err = -ENOMEM;
+			if (order < min_order)
+				order = min_order;
 			if (order > 0)
 				alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN;
+
+			VM_BUG_ON(index & ((1UL << order) - 1));
+
 			folio = filemap_alloc_folio(alloc_gfp, order);
 			if (!folio)
 				continue;
@@ -1927,7 +1941,7 @@  struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 				break;
 			folio_put(folio);
 			folio = NULL;
-		} while (order-- > 0);
+		} while (order-- > min_order);
 
 		if (err == -EEXIST)
 			goto repeat;
@@ -2422,7 +2436,8 @@  static int filemap_create_folio(struct file *file,
 	struct folio *folio;
 	int error;
 
-	folio = filemap_alloc_folio(mapping_gfp_mask(mapping), 0);
+	folio = filemap_alloc_folio(mapping_gfp_mask(mapping),
+				    mapping_min_folio_order(mapping));
 	if (!folio)
 		return -ENOMEM;
 
@@ -3666,7 +3681,8 @@  static struct folio *do_read_cache_folio(struct address_space *mapping,
 repeat:
 	folio = filemap_get_folio(mapping, index);
 	if (IS_ERR(folio)) {
-		folio = filemap_alloc_folio(gfp, 0);
+		folio = filemap_alloc_folio(gfp,
+					    mapping_min_folio_order(mapping));
 		if (!folio)
 			return ERR_PTR(-ENOMEM);
 		err = filemap_add_folio(mapping, folio, index, gfp);