2023-09-15 20:42:15

by Pankaj Raghav (Samsung)

Subject: [RFC 07/23] filemap: align the index to mapping_min_order in __filemap_add_folio()

From: Luis Chamberlain <[email protected]>

Align the index to the mapping_min_order number of pages while setting
the XA_STATE and xas_set_order().

Signed-off-by: Luis Chamberlain <[email protected]>
---
mm/filemap.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 33de71bfa953..15bc810bfc89 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -859,7 +859,10 @@ EXPORT_SYMBOL_GPL(replace_page_cache_folio);
noinline int __filemap_add_folio(struct address_space *mapping,
struct folio *folio, pgoff_t index, gfp_t gfp, void **shadowp)
{
- XA_STATE(xas, &mapping->i_pages, index);
+ unsigned int min_order = mapping_min_folio_order(mapping);
+ unsigned int nr_of_pages = (1U << min_order);
+ pgoff_t rounded_index = round_down(index, nr_of_pages);
+ XA_STATE(xas, &mapping->i_pages, rounded_index);
int huge = folio_test_hugetlb(folio);
bool charged = false;
long nr = 1;
@@ -875,8 +878,8 @@ noinline int __filemap_add_folio(struct address_space *mapping,
charged = true;
}

- VM_BUG_ON_FOLIO(index & (folio_nr_pages(folio) - 1), folio);
- xas_set_order(&xas, index, folio_order(folio));
+ VM_BUG_ON_FOLIO(rounded_index & (folio_nr_pages(folio) - 1), folio);
+ xas_set_order(&xas, rounded_index, folio_order(folio));
nr = folio_nr_pages(folio);

gfp &= GFP_RECLAIM_MASK;
@@ -913,6 +916,7 @@ noinline int __filemap_add_folio(struct address_space *mapping,
}
}

+ VM_BUG_ON_FOLIO(folio_order(folio) < min_order, folio);
xas_store(&xas, folio);
if (xas_error(&xas))
goto unlock;
--
2.40.1

2023-09-15 22:56:23

by Matthew Wilcox

Subject: Re: [RFC 07/23] filemap: align the index to mapping_min_order in __filemap_add_folio()

On Fri, Sep 15, 2023 at 08:38:32PM +0200, Pankaj Raghav wrote:
> From: Luis Chamberlain <[email protected]>
>
> Align the index to the mapping_min_order number of pages while setting
> the XA_STATE and xas_set_order().

Not sure why this one's necessary either. The index should already be
aligned to folio_order.

Some bits of it are clearly needed, like checking that folio_order() >=
min_order.

2023-09-19 00:28:13

by Luis Chamberlain

Subject: Re: [RFC 07/23] filemap: align the index to mapping_min_order in __filemap_add_folio()

On Fri, Sep 15, 2023 at 08:48:43PM +0100, Matthew Wilcox wrote:
> On Fri, Sep 15, 2023 at 08:38:32PM +0200, Pankaj Raghav wrote:
> > From: Luis Chamberlain <[email protected]>
> >
> > Align the index to the mapping_min_order number of pages while setting
> > the XA_STATE and xas_set_order().
>
> Not sure why this one's necessary either. The index should already be
> aligned to folio_order.

Oh, it was not obvious, would a VM_BUG_ON_FOLIO() be OK then?

> Some bits of it are clearly needed, like checking that folio_order() >=
> min_order.

Thanks,

Luis