iomap: hold state_lock over call to ifs_set_range_uptodate()

Patch series "Add folio_end_read", v2.

The core of this patchset is the new folio_end_read() call which
filesystems can use when finishing a page cache read instead of separate
calls to mark the folio uptodate and unlock it.  As an illustration of its
use, I converted ext4, iomap & mpage; more can be converted.

I think that's useful by itself, but the interesting optimisation is that
we can implement that with a single XOR instruction that sets the uptodate
bit, clears the lock bit, tests the waiter bit and provides a write memory
barrier.  That removes one memory barrier and one atomic instruction from
each page read, which seems worth doing.  That's in patch 15.

The last two patches could be a separate series, but basically we can do
the same thing with the writeback flag that we do with the unlock flag;
clear it and test the waiters bit at the same time.


This patch (of 17):

This is really preparation for the next patch, but it lets us call
folio_mark_uptodate() in just one place instead of two.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: "Theodore Ts'o" <[email protected]>
Cc: Andreas Dilger <[email protected]>
Cc: Richard Henderson <[email protected]>
Cc: Ivan Kokshaysky <[email protected]>
Cc: Matt Turner <[email protected]>
Cc: Thomas Bogendoerfer <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Paul Walmsley <[email protected]>
Cc: Palmer Dabbelt <[email protected]>
Cc: Albert Ou <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Vasily Gorbik <[email protected]>
Cc: Alexander Gordeev <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: Sven Schnelle <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Matthew Wilcox (Oracle)

fs/iomap/buffered-io.c

@@ -57,30 +57,32 @@ static inline bool ifs_block_is_uptodate(struct iomap_folio_state *ifs,
 	return test_bit(block, ifs->state);
 }
 
-static void ifs_set_range_uptodate(struct folio *folio,
+static bool ifs_set_range_uptodate(struct folio *folio,
 		struct iomap_folio_state *ifs, size_t off, size_t len)
 {
 	struct inode *inode = folio->mapping->host;
 	unsigned int first_blk = off >> inode->i_blkbits;
 	unsigned int last_blk = (off + len - 1) >> inode->i_blkbits;
 	unsigned int nr_blks = last_blk - first_blk + 1;
-	unsigned long flags;
 
-	spin_lock_irqsave(&ifs->state_lock, flags);
 	bitmap_set(ifs->state, first_blk, nr_blks);
-	if (ifs_is_fully_uptodate(folio, ifs))
-		folio_mark_uptodate(folio);
-	spin_unlock_irqrestore(&ifs->state_lock, flags);
+	return ifs_is_fully_uptodate(folio, ifs);
 }
 
 static void iomap_set_range_uptodate(struct folio *folio, size_t off,
 		size_t len)
 {
 	struct iomap_folio_state *ifs = folio->private;
+	unsigned long flags;
+	bool uptodate = true;
 
-	if (ifs)
-		ifs_set_range_uptodate(folio, ifs, off, len);
-	else
+	if (ifs) {
+		spin_lock_irqsave(&ifs->state_lock, flags);
+		uptodate = ifs_set_range_uptodate(folio, ifs, off, len);
+		spin_unlock_irqrestore(&ifs->state_lock, flags);
+	}
+
+	if (uptodate)
 		folio_mark_uptodate(folio);
 }