diff mbox series

[13/21] iomap: Convert readahead and readpage to use a folio

Message ID 20211101203929.954622-14-willy@infradead.org (mailing list archive)
State New, archived
Headers show
Series iomap/xfs folio patches | expand

Commit Message

Matthew Wilcox (Oracle) Nov. 1, 2021, 8:39 p.m. UTC 
Handle folios of arbitrary size instead of working in PAGE_SIZE units.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
---
 fs/iomap/buffered-io.c | 53 +++++++++++++++++++++---------------------
 1 file changed, 26 insertions(+), 27 deletions(-)

Comments

Christoph Hellwig Nov. 2, 2021, 7:20 a.m. UTC | #1 
On Mon, Nov 01, 2021 at 08:39:21PM +0000, Matthew Wilcox (Oracle) wrote:
>  	for (done = 0; done < length; done += ret) {
> -		if (ctx->cur_page && offset_in_page(iter->pos + done) == 0) {
> -			if (!ctx->cur_page_in_bio)
> -				unlock_page(ctx->cur_page);
> -			put_page(ctx->cur_page);
> -			ctx->cur_page = NULL;
> +		if (ctx->cur_folio &&
> +		    offset_in_folio(ctx->cur_folio, iter->pos + done) == 0) {
> +			if (!ctx->cur_folio_in_bio)
> +				folio_unlock(ctx->cur_folio);
> +			ctx->cur_folio = NULL;

Where did the put_page here disappear to?

> @@ -403,10 +403,9 @@ void iomap_readahead(struct readahead_control *rac, const struct iomap_ops *ops)
>  
>  	if (ctx.bio)
>  		submit_bio(ctx.bio);
> -	if (ctx.cur_page) {
> -		if (!ctx.cur_page_in_bio)
> -			unlock_page(ctx.cur_page);
> -		put_page(ctx.cur_page);
> +	if (ctx.cur_folio) {
> +		if (!ctx.cur_folio_in_bio)
> +			folio_unlock(ctx.cur_folio);

... and here?
Matthew Wilcox (Oracle) Nov. 2, 2021, 12:28 p.m. UTC | #2 
On Tue, Nov 02, 2021 at 12:20:47AM -0700, Christoph Hellwig wrote:
> On Mon, Nov 01, 2021 at 08:39:21PM +0000, Matthew Wilcox (Oracle) wrote:
> >  	for (done = 0; done < length; done += ret) {
> > -		if (ctx->cur_page && offset_in_page(iter->pos + done) == 0) {
> > -			if (!ctx->cur_page_in_bio)
> > -				unlock_page(ctx->cur_page);
> > -			put_page(ctx->cur_page);
> > -			ctx->cur_page = NULL;
> > +		if (ctx->cur_folio &&
> > +		    offset_in_folio(ctx->cur_folio, iter->pos + done) == 0) {
> > +			if (!ctx->cur_folio_in_bio)
> > +				folio_unlock(ctx->cur_folio);
> > +			ctx->cur_folio = NULL;
> 
> Where did the put_page here disappear to?

I'll put that explanation in the changelog:

Handle folios of arbitrary size instead of working in PAGE_SIZE units.
readahead_folio() puts the page for you, so this is not quite a mechanical
change.

---

The reason for making that change is that I messed up when introducing the
readahead() operation.  I followed the refcounting rule of ->readpages()
instead of the rule of ->readpage().  For a successful readahead, we have
two more atomic operations than necessary.  I want to fix that, and
this seems like a good opportunity to do it.  Once all filesystems are
converted to call readahead_folio(), we can remove the extra get_page()
and put_page().

I did put an explanation of that in commit 9bf70167e3c6, but it's not
reasonable to expect reviewers to remember that when reviewing changes
to their filesystem's readahead, so I'll be sure to mention it in any
future conversion's changelogs.

    mm/filemap: Add readahead_folio()

    The pointers stored in the page cache are folios, by definition.
    This change comes with a behaviour change -- callers of readahead_folio()
    are no longer required to put the page reference themselves.  This matches
    how readpage works, rather than matching how readpages used to work.
diff mbox series

Patch

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index b5e77d9de4a7..3c68ff26cd16 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -188,8 +188,8 @@  static void iomap_read_end_io(struct bio *bio)
 }
 
 struct iomap_readpage_ctx {
-	struct page		*cur_page;
-	bool			cur_page_in_bio;
+	struct folio		*cur_folio;
+	bool			cur_folio_in_bio;
 	struct bio		*bio;
 	struct readahead_control *rac;
 };
@@ -243,8 +243,7 @@  static loff_t iomap_readpage_iter(const struct iomap_iter *iter,
 	const struct iomap *iomap = &iter->iomap;
 	loff_t pos = iter->pos + offset;
 	loff_t length = iomap_length(iter) - offset;
-	struct page *page = ctx->cur_page;
-	struct folio *folio = page_folio(page);
+	struct folio *folio = ctx->cur_folio;
 	struct iomap_page *iop;
 	loff_t orig_pos = pos;
 	size_t poff, plen;
@@ -265,7 +264,7 @@  static loff_t iomap_readpage_iter(const struct iomap_iter *iter,
 		goto done;
 	}
 
-	ctx->cur_page_in_bio = true;
+	ctx->cur_folio_in_bio = true;
 	if (iop)
 		atomic_add(plen, &iop->read_bytes_pending);
 
@@ -273,7 +272,7 @@  static loff_t iomap_readpage_iter(const struct iomap_iter *iter,
 	if (!ctx->bio ||
 	    bio_end_sector(ctx->bio) != sector ||
 	    !bio_add_folio(ctx->bio, folio, plen, poff)) {
-		gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
+		gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
 		gfp_t orig_gfp = gfp;
 		unsigned int nr_vecs = DIV_ROUND_UP(length, PAGE_SIZE);
 
@@ -312,30 +311,31 @@  static loff_t iomap_readpage_iter(const struct iomap_iter *iter,
 int
 iomap_readpage(struct page *page, const struct iomap_ops *ops)
 {
+	struct folio *folio = page_folio(page);
 	struct iomap_iter iter = {
-		.inode		= page->mapping->host,
-		.pos		= page_offset(page),
-		.len		= PAGE_SIZE,
+		.inode		= folio->mapping->host,
+		.pos		= folio_pos(folio),
+		.len		= folio_size(folio),
 	};
 	struct iomap_readpage_ctx ctx = {
-		.cur_page	= page,
+		.cur_folio	= folio,
 	};
 	int ret;
 
-	trace_iomap_readpage(page->mapping->host, 1);
+	trace_iomap_readpage(iter.inode, 1);
 
 	while ((ret = iomap_iter(&iter, ops)) > 0)
 		iter.processed = iomap_readpage_iter(&iter, &ctx, 0);
 
 	if (ret < 0)
-		SetPageError(page);
+		folio_set_error(folio);
 
 	if (ctx.bio) {
 		submit_bio(ctx.bio);
-		WARN_ON_ONCE(!ctx.cur_page_in_bio);
+		WARN_ON_ONCE(!ctx.cur_folio_in_bio);
 	} else {
-		WARN_ON_ONCE(ctx.cur_page_in_bio);
-		unlock_page(page);
+		WARN_ON_ONCE(ctx.cur_folio_in_bio);
+		folio_unlock(folio);
 	}
 
 	/*
@@ -354,15 +354,15 @@  static loff_t iomap_readahead_iter(const struct iomap_iter *iter,
 	loff_t done, ret;
 
 	for (done = 0; done < length; done += ret) {
-		if (ctx->cur_page && offset_in_page(iter->pos + done) == 0) {
-			if (!ctx->cur_page_in_bio)
-				unlock_page(ctx->cur_page);
-			put_page(ctx->cur_page);
-			ctx->cur_page = NULL;
+		if (ctx->cur_folio &&
+		    offset_in_folio(ctx->cur_folio, iter->pos + done) == 0) {
+			if (!ctx->cur_folio_in_bio)
+				folio_unlock(ctx->cur_folio);
+			ctx->cur_folio = NULL;
 		}
-		if (!ctx->cur_page) {
-			ctx->cur_page = readahead_page(ctx->rac);
-			ctx->cur_page_in_bio = false;
+		if (!ctx->cur_folio) {
+			ctx->cur_folio = readahead_folio(ctx->rac);
+			ctx->cur_folio_in_bio = false;
 		}
 		ret = iomap_readpage_iter(iter, ctx, done);
 	}
@@ -403,10 +403,9 @@  void iomap_readahead(struct readahead_control *rac, const struct iomap_ops *ops)
 
 	if (ctx.bio)
 		submit_bio(ctx.bio);
-	if (ctx.cur_page) {
-		if (!ctx.cur_page_in_bio)
-			unlock_page(ctx.cur_page);
-		put_page(ctx.cur_page);
+	if (ctx.cur_folio) {
+		if (!ctx.cur_folio_in_bio)
+			folio_unlock(ctx.cur_folio);
 	}
 }
 EXPORT_SYMBOL_GPL(iomap_readahead);