diff mbox series

[RFCv3,2/3] iomap: Change uptodate variable name to state

Message ID 457680a57d7c581aae81def50773ed96034af420.1677428794.git.ritesh.list@gmail.com (mailing list archive)
State New, archived
Headers show
Series iomap: Add support for subpage dirty state tracking to improve write performance | expand

Commit Message

Ritesh Harjani (IBM) Feb. 26, 2023, 7:43 p.m. UTC 
This patch changes the struct iomap_page uptodate & uptodate_lock
member names to state and state_lock to better reflect their purpose
for the upcoming patch. It also introduces the accessor functions for
updating uptodate state bits in iop->state bitmap. This makes the code
easy to understand on when different bitmap types are getting referred
in different code paths.

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 fs/iomap/buffered-io.c | 65 ++++++++++++++++++++++++++++++++----------
 1 file changed, 50 insertions(+), 15 deletions(-)

Comments

Dave Chinner Feb. 26, 2023, 11:12 p.m. UTC | #1 
On Mon, Feb 27, 2023 at 01:13:31AM +0530, Ritesh Harjani (IBM) wrote:
> This patch changes the struct iomap_page uptodate & uptodate_lock
> member names to state and state_lock to better reflect their purpose
> for the upcoming patch. It also introduces the accessor functions for
> updating uptodate state bits in iop->state bitmap. This makes the code
> easy to understand on when different bitmap types are getting referred
> in different code paths.
> 
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
> ---
>  fs/iomap/buffered-io.c | 65 ++++++++++++++++++++++++++++++++----------
>  1 file changed, 50 insertions(+), 15 deletions(-)
....

The mechanical change itself looks fine, so from that perspective:

Reviewed-by: Dave Chinner <dchinner@redhat.com>

However, I'm wondering about the efficiency of these bit searches.

> @@ -110,7 +143,7 @@ static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
>  
>  		/* move forward for each leading block marked uptodate */
>  		for (i = first; i <= last; i++) {
> -			if (!test_bit(i, iop->uptodate))
> +			if (!iop_test_uptodate(iop, i, nr_blocks))
>  				break;
>  			*pos += block_size;
>  			poff += block_size;

Looking at this code, it could have been written to use
find_first_zero_bit() rather than testing each bit individually...

> @@ -120,7 +153,7 @@ static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
>  
>  		/* truncate len if we find any trailing uptodate block(s) */
>  		for ( ; i <= last; i++) {
> -			if (test_bit(i, iop->uptodate)) {
> +			if (iop_test_uptodate(iop, i, nr_blocks)) {
>  				plen -= (last - i + 1) * block_size;
>  				last = i - 1;
>  				break;

And this is find_first_bit()...

>  static void iomap_set_range_uptodate(struct folio *folio,
> @@ -439,6 +473,7 @@ bool iomap_is_partially_uptodate(struct folio *folio, size_t from, size_t count)
>  	struct iomap_page *iop = to_iomap_page(folio);
>  	struct inode *inode = folio->mapping->host;
>  	unsigned first, last, i;
> +	unsigned int nr_blocks = i_blocks_per_folio(inode, folio);
>  
>  	if (!iop)
>  		return false;
> @@ -451,7 +486,7 @@ bool iomap_is_partially_uptodate(struct folio *folio, size_t from, size_t count)
>  	last = (from + count - 1) >> inode->i_blkbits;
>  
>  	for (i = first; i <= last; i++)
> -		if (!test_bit(i, iop->uptodate))
> +		if (!iop_test_uptodate(iop, i, nr_blocks))
>  			return false;

Again, find_first_zero_bit().

These seem like worthwhile optimisations in light of the heavier use
these bitmaps will get with sub-folio dirty tracking, especially
considering large folios will now use these paths. Do these
interface changes preclude the use of efficient bitmap searching
functions?

-Dave.
Matthew Wilcox Feb. 26, 2023, 11:23 p.m. UTC | #2 
On Mon, Feb 27, 2023 at 01:13:31AM +0530, Ritesh Harjani (IBM) wrote:
> +static inline bool iop_test_uptodate(struct iomap_page *iop, unsigned int pos,
> +				unsigned int nrblocks)
> +{
> +	return test_bit(pos, iop->state);
> +}

'pos' is usually position within file, not within the folio.  That
should be called 'block' or 'start' like the other accessors.

> +static inline bool iop_full_uptodate(struct iomap_page *iop,
> +				unsigned int nrblocks)
> +{
> +	return bitmap_full(iop->state, nrblocks);
> +}

Not sure I like iop_full_uptodate() as a name.  iop_entirely_uptodate()?
iop_folio_uptodate()?  iop_all_uptodate()?
Ritesh Harjani (IBM) Feb. 28, 2023, 6:38 p.m. UTC | #3 
Matthew Wilcox <willy@infradead.org> writes:

> On Mon, Feb 27, 2023 at 01:13:31AM +0530, Ritesh Harjani (IBM) wrote:
>> +static inline bool iop_test_uptodate(struct iomap_page *iop, unsigned int pos,
>> +				unsigned int nrblocks)
>> +{
>> +	return test_bit(pos, iop->state);
>> +}
>
> 'pos' is usually position within file, not within the folio.  That
> should be called 'block' or 'start' like the other accessors.

Agreed. Will make the change in next rev.

>
>> +static inline bool iop_full_uptodate(struct iomap_page *iop,
>> +				unsigned int nrblocks)
>> +{
>> +	return bitmap_full(iop->state, nrblocks);
>> +}
>
> Not sure I like iop_full_uptodate() as a name.  iop_entirely_uptodate()?
> iop_folio_uptodate()?  iop_all_uptodate()?

I can settle for iop_all_uptodate(). But would you rather prefer
iop_uptodate_full() like bitmap_full()?

-ritesh
diff mbox series

Patch

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index c5b51ab1184e..e0b0be16278e 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -25,13 +25,13 @@ 
 
 /*
  * Structure allocated for each folio when block size < folio size
- * to track sub-folio uptodate status and I/O completions.
+ * to track sub-folio uptodate state and I/O completions.
  */
 struct iomap_page {
 	atomic_t		read_bytes_pending;
 	atomic_t		write_bytes_pending;
-	spinlock_t		uptodate_lock;
-	unsigned long		uptodate[];
+	spinlock_t		state_lock;
+	unsigned long		state[];
 };
 
 static inline struct iomap_page *to_iomap_page(struct folio *folio)
@@ -43,6 +43,38 @@  static inline struct iomap_page *to_iomap_page(struct folio *folio)
 
 static struct bio_set iomap_ioend_bioset;
 
+/*
+ * Accessor functions for setting/clearing/checking uptodate bits in
+ * iop->state bitmap.
+ * nrblocks is i_blocks_per_folio() which is passed in every
+ * function as the last argument for API consistency.
+ */
+static inline void iop_set_range_uptodate(struct iomap_page *iop,
+				unsigned int start, unsigned int len,
+				unsigned int nrblocks)
+{
+	bitmap_set(iop->state, start, len);
+}
+
+static inline void iop_clear_range_uptodate(struct iomap_page *iop,
+				unsigned int start, unsigned int len,
+				unsigned int nrblocks)
+{
+	bitmap_clear(iop->state, start, len);
+}
+
+static inline bool iop_test_uptodate(struct iomap_page *iop, unsigned int pos,
+				unsigned int nrblocks)
+{
+	return test_bit(pos, iop->state);
+}
+
+static inline bool iop_full_uptodate(struct iomap_page *iop,
+				unsigned int nrblocks)
+{
+	return bitmap_full(iop->state, nrblocks);
+}
+
 static struct iomap_page *
 iomap_page_create(struct inode *inode, struct folio *folio, unsigned int flags)
 {
@@ -58,12 +90,12 @@  iomap_page_create(struct inode *inode, struct folio *folio, unsigned int flags)
 	else
 		gfp = GFP_NOFS | __GFP_NOFAIL;
 
-	iop = kzalloc(struct_size(iop, uptodate, BITS_TO_LONGS(nr_blocks)),
+	iop = kzalloc(struct_size(iop, state, BITS_TO_LONGS(nr_blocks)),
 		      gfp);
 	if (iop) {
-		spin_lock_init(&iop->uptodate_lock);
+		spin_lock_init(&iop->state_lock);
 		if (folio_test_uptodate(folio))
-			bitmap_fill(iop->uptodate, nr_blocks);
+			iop_set_range_uptodate(iop, 0, nr_blocks, nr_blocks);
 		folio_attach_private(folio, iop);
 	}
 	return iop;
@@ -79,7 +111,7 @@  static void iomap_page_release(struct folio *folio)
 		return;
 	WARN_ON_ONCE(atomic_read(&iop->read_bytes_pending));
 	WARN_ON_ONCE(atomic_read(&iop->write_bytes_pending));
-	WARN_ON_ONCE(bitmap_full(iop->uptodate, nr_blocks) !=
+	WARN_ON_ONCE(iop_full_uptodate(iop, nr_blocks) !=
 			folio_test_uptodate(folio));
 	kfree(iop);
 }
@@ -99,6 +131,7 @@  static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
 	size_t plen = min_t(loff_t, folio_size(folio) - poff, length);
 	unsigned first = poff >> block_bits;
 	unsigned last = (poff + plen - 1) >> block_bits;
+	unsigned int nr_blocks = i_blocks_per_folio(inode, folio);
 
 	/*
 	 * If the block size is smaller than the page size, we need to check the
@@ -110,7 +143,7 @@  static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
 
 		/* move forward for each leading block marked uptodate */
 		for (i = first; i <= last; i++) {
-			if (!test_bit(i, iop->uptodate))
+			if (!iop_test_uptodate(iop, i, nr_blocks))
 				break;
 			*pos += block_size;
 			poff += block_size;
@@ -120,7 +153,7 @@  static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
 
 		/* truncate len if we find any trailing uptodate block(s) */
 		for ( ; i <= last; i++) {
-			if (test_bit(i, iop->uptodate)) {
+			if (iop_test_uptodate(iop, i, nr_blocks)) {
 				plen -= (last - i + 1) * block_size;
 				last = i - 1;
 				break;
@@ -151,12 +184,13 @@  static void iomap_iop_set_range_uptodate(struct folio *folio,
 	unsigned first = off >> inode->i_blkbits;
 	unsigned last = (off + len - 1) >> inode->i_blkbits;
 	unsigned long flags;
+	unsigned int nr_blocks = i_blocks_per_folio(inode, folio);
 
-	spin_lock_irqsave(&iop->uptodate_lock, flags);
-	bitmap_set(iop->uptodate, first, last - first + 1);
-	if (bitmap_full(iop->uptodate, i_blocks_per_folio(inode, folio)))
+	spin_lock_irqsave(&iop->state_lock, flags);
+	iop_set_range_uptodate(iop, first, last - first + 1, nr_blocks);
+	if (iop_full_uptodate(iop, nr_blocks))
 		folio_mark_uptodate(folio);
-	spin_unlock_irqrestore(&iop->uptodate_lock, flags);
+	spin_unlock_irqrestore(&iop->state_lock, flags);
 }
 
 static void iomap_set_range_uptodate(struct folio *folio,
@@ -439,6 +473,7 @@  bool iomap_is_partially_uptodate(struct folio *folio, size_t from, size_t count)
 	struct iomap_page *iop = to_iomap_page(folio);
 	struct inode *inode = folio->mapping->host;
 	unsigned first, last, i;
+	unsigned int nr_blocks = i_blocks_per_folio(inode, folio);
 
 	if (!iop)
 		return false;
@@ -451,7 +486,7 @@  bool iomap_is_partially_uptodate(struct folio *folio, size_t from, size_t count)
 	last = (from + count - 1) >> inode->i_blkbits;
 
 	for (i = first; i <= last; i++)
-		if (!test_bit(i, iop->uptodate))
+		if (!iop_test_uptodate(iop, i, nr_blocks))
 			return false;
 	return true;
 }
@@ -1611,7 +1646,7 @@  iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 	 * invalid, grab a new one.
 	 */
 	for (i = 0; i < nblocks && pos < end_pos; i++, pos += len) {
-		if (iop && !test_bit(i, iop->uptodate))
+		if (iop && !iop_test_uptodate(iop, i, nblocks))
 			continue;
 
 		error = wpc->ops->map_blocks(wpc, inode, pos);