linux-kernel - [PATCH 11/15] mm: add FGP_UNCACHED folio creation flag

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Message-ID: <20241110152906.1747545-12-axboe@kernel.dk>
Date: Sun, 10 Nov 2024 08:28:03 -0700
From: Jens Axboe <axboe@...nel.dk>
To: linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org
Cc: hannes@...xchg.org,
	clm@...a.com,
	linux-kernel@...r.kernel.org,
	willy@...radead.org,
	Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 11/15] mm: add FGP_UNCACHED folio creation flag

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.

Signed-off-by: Jens Axboe <axboe@...nel.dk>
---
 include/linux/pagemap.h | 2 ++
 mm/filemap.c            | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 5469664f66c3..de0ed906cd2d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -741,6 +741,7 @@ 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.
  */
@@ -754,6 +755,7 @@ 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 cfbfc8b14b1f..4fdf3c4ae00f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1987,6 +1987,8 @@ 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)
-- 
2.45.2