[PATCH v3 6/8] filemap: Allow __filemap_get_folio to allocate large folios

Matthew Wilcox (Oracle)
2023-06-12T20:40:09Z

Allow callers of __filemap_get_folio() to specify a preferred folio
order in the FGP flags. This is only honoured in the FGP_CREATE path;
if there is already a folio in the page cache that covers the index,
we will return it, no matter what its order is. No create-around is
attempted; we will only create folios which start at the specified index.
Unmodified callers will continue to allocate order 0 folios.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
include/linux/pagemap.h | 23 ++++++++++++++++++++++
mm/filemap.c | 42 ++++++++++++++++++++++++++++-------------
mm/readahead.c | 13 -------------
3 files changed, 52 insertions(+), 26 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 993242f0c1e1..b2ed80f91e5b 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -466,6 +466,19 @@ static inline void *detach_page_private(struct page *page)
return folio_detach_private(page_folio(page));
}

+/*
+ * There are some parts of the kernel which assume that PMD entries
+ * are exactly HPAGE_PMD_ORDER. Those should be fixed, but until then,
+ * limit the maximum allocation order to PMD size. I'm not aware of any
+ * assumptions about maximum order if THP are disabled, but 8 seems like
+ * a good order (that's 1MB if you're using 4kB pages)
+ */
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#define MAX_PAGECACHE_ORDER HPAGE_PMD_ORDER
+#else
+#define MAX_PAGECACHE_ORDER 8
+#endif
+
#ifdef CONFIG_NUMA
struct folio *filemap_alloc_folio(gfp_t gfp, unsigned int order);
#else
@@ -531,9 +544,19 @@ typedef unsigned int __bitwise fgf_t;
#define FGP_NOWAIT ((__force fgf_t)0x00000020)
#define FGP_FOR_MMAP ((__force fgf_t)0x00000040)
#define FGP_STABLE ((__force fgf_t)0x00000080)
+#define FGF_GET_ORDER(fgf) (((__force unsigned)fgf) >> 26) /* top 6 bits */

#define FGP_WRITEBEGIN (FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE)

+static inline fgf_t fgf_set_order(size_t size)
+{
+ unsigned int shift = ilog2(size);
+
+ if (shift <= PAGE_SHIFT)
+ return 0;
+ return (__force fgf_t)((shift - PAGE_SHIFT) << 26);
+}
+
void *filemap_get_entry(struct address_space *mapping, pgoff_t index);
struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
fgf_t fgp_flags, gfp_t gfp);
diff --git a/mm/filemap.c b/mm/filemap.c
index 42353b82ebf6..bd66398ae072 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1937,7 +1937,9 @@ 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);
int err;
+
if ((fgp_flags & FGP_WRITE) && mapping_can_writeback(mapping))
gfp |= __GFP_WRITE;
if (fgp_flags & FGP_NOFS)
@@ -1946,26 +1948,40 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
gfp &= ~GFP_KERNEL;
gfp |= GFP_NOWAIT | __GFP_NOWARN;
}
-
- folio = filemap_alloc_folio(gfp, 0);
- if (!folio)
- return ERR_PTR(-ENOMEM);
-
if (WARN_ON_ONCE(!(fgp_flags & (FGP_LOCK | FGP_FOR_MMAP))))
fgp_flags |= FGP_LOCK;

- /* Init accessed so avoid atomic mark_page_accessed later */
- if (fgp_flags & FGP_ACCESSED)
- __folio_set_referenced(folio);
+ if (!mapping_large_folio_support(mapping))
+ order = 0;
+ if (order > MAX_PAGECACHE_ORDER)
+ order = MAX_PAGECACHE_ORDER;
+ /* If we're not aligned, allocate a smaller folio */
+ if (index & ((1UL << order) - 1))
+ order = __ffs(index);

- err = filemap_add_folio(mapping, folio, index, gfp);
- if (unlikely(err)) {
+ do {
+ err = -ENOMEM;
+ if (order == 1)
+ order = 0;
+ folio = filemap_alloc_folio(gfp, order);
+ if (!folio)
+ continue;
+
+ /* Init accessed so avoid atomic mark_page_accessed later */
+ if (fgp_flags & FGP_ACCESSED)
+ __folio_set_referenced(folio);
+
+ err = filemap_add_folio(mapping, folio, index, gfp);
+ if (!err)
+ break;
folio_put(folio);
folio = NULL;
- if (err == -EEXIST)
- goto repeat;
- }
+ } while (order-- > 0);

+ if (err == -EEXIST)
+ goto repeat;
+ if (err)
+ return ERR_PTR(err);
/*
* filemap_add_folio locks the page, and for mmap
* we expect an unlocked page.
diff --git a/mm/readahead.c b/mm/readahead.c
index 47afbca1d122..59a071badb90 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -462,19 +462,6 @@ static int try_context_readahead(struct address_space *mapping,
return 1;
}

-/*
- * There are some parts of the kernel which assume that PMD entries
- * are exactly HPAGE_PMD_ORDER. Those should be fixed, but until then,
- * limit the maximum allocation order to PMD size. I'm not aware of any
- * assumptions about maximum order if THP are disabled, but 8 seems like
- * a good order (that's 1MB if you're using 4kB pages)
- */
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-#define MAX_PAGECACHE_ORDER HPAGE_PMD_ORDER
-#else
-#define MAX_PAGECACHE_ORDER 8
-#endif
-
static inline int ra_alloc_folio(struct readahead_control *ractl, pgoff_t index,
pgoff_t mark, unsigned int order, gfp_t gfp)
{
--
2.39.2