[PATCH 12/17] mm: add FGP_UNCACHED folio creation flag

Jens Axboe
2024-11-14T15:28:19Z

Callers can pass this in for uncached folio creation, in which case if
a folio is newly created it gets marked as uncached. If a folio exists
for this index and lookup succeeds, then it will not get marked as
uncached. If an !uncached lookup finds a cached folio, clear the flag.
For that case, there are competeting uncached and cached users of the
folio, and it should not get pruned.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
include/linux/pagemap.h | 2 ++
mm/filemap.c | 5 +++++
2 files changed, 7 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index cc02518d338d..860807e34b8c 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -721,6 +721,7 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
* * %FGP_NOFS - __GFP_FS will get cleared in gfp.
* * %FGP_NOWAIT - Don't block on the folio lock.
* * %FGP_STABLE - Wait for the folio to be stable (finished writeback)
+ * * %FGP_UNCACHED - Uncached buffered IO
* * %FGP_WRITEBEGIN - The flags to use in a filesystem write_begin()
* implementation.
*/
@@ -734,6 +735,7 @@ 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 FGP_UNCACHED ((__force fgf_t)0x00000100)
#define FGF_GET_ORDER(fgf) (((__force unsigned)fgf) >> 26) /* top 6 bits */

#define FGP_WRITEBEGIN (FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE)
diff --git a/mm/filemap.c b/mm/filemap.c
index a8a9fb986d2d..dbc3fa975ad1 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2002,6 +2002,8 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
/* Init accessed so avoid atomic mark_page_accessed later */
if (fgp_flags & FGP_ACCESSED)
__folio_set_referenced(folio);
+ if (fgp_flags & FGP_UNCACHED)
+ __folio_set_uncached(folio);

err = filemap_add_folio(mapping, folio, index, gfp);
if (!err)
@@ -2024,6 +2026,9 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,

if (!folio)
return ERR_PTR(-ENOENT);
+ /* not an uncached lookup, clear uncached if set */
+ if (folio_test_uncached(folio) && !(fgp_flags & FGP_UNCACHED))
+ folio_clear_uncached(folio);
return folio;
}
EXPORT_SYMBOL(__filemap_get_folio);
--
2.45.2