[PATCH v3 07/15] iomap: track read/readahead folio ownership internally

Joanne Koong
2025-09-16T23:50:38Z

The purpose of "struct iomap_read_folio_ctx->cur_folio_in_bio" is to
track folio ownership to know who is responsible for unlocking it.
Rename "cur_folio_in_bio" to "cur_folio_owned" to better reflect this
purpose and so that this can be generically used later on by filesystems
that are not block-based.

Since "struct iomap_read_folio_ctx" will be made a public interface
later on when read/readahead takes in caller-provided callbacks, track
the folio ownership state internally instead of exposing it in "struct
iomap_read_folio_ctx" to make the interface simpler for end users.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
fs/iomap/buffered-io.c | 34 +++++++++++++++++++++++-----------
1 file changed, 23 insertions(+), 11 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 6c5a631848b7..587bbdbd24bc 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -352,7 +352,6 @@ static void iomap_read_end_io(struct bio *bio)

struct iomap_read_folio_ctx {
struct folio *cur_folio;
- bool cur_folio_in_bio;
void *read_ctx;
struct readahead_control *rac;
};
@@ -376,7 +375,6 @@ static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
sector_t sector;
struct bio *bio = ctx->read_ctx;

- ctx->cur_folio_in_bio = true;
if (ifs) {
spin_lock_irq(&ifs->state_lock);
ifs->read_bytes_pending += plen;
@@ -413,7 +411,7 @@ static void iomap_bio_read_folio_range(const struct iomap_iter *iter,
}

static int iomap_read_folio_iter(struct iomap_iter *iter,
- struct iomap_read_folio_ctx *ctx)
+ struct iomap_read_folio_ctx *ctx, bool *cur_folio_owned)
{
const struct iomap *iomap = &iter->iomap;
loff_t pos = iter->pos;
@@ -450,6 +448,7 @@ static int iomap_read_folio_iter(struct iomap_iter *iter,
folio_zero_range(folio, poff, plen);
iomap_set_range_uptodate(folio, poff, plen);
} else {
+ *cur_folio_owned = true;
iomap_bio_read_folio_range(iter, ctx, pos, plen);
}

@@ -472,16 +471,22 @@ int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
struct iomap_read_folio_ctx ctx = {
.cur_folio = folio,
};
+ /*
+ * If an external IO helper takes ownership of the folio, it is
+ * responsible for unlocking it when the read completes.
+ */
+ bool cur_folio_owned = false;
int ret;

trace_iomap_readpage(iter.inode, 1);

while ((ret = iomap_iter(&iter, ops)) > 0)
- iter.status = iomap_read_folio_iter(&iter, &ctx);
+ iter.status = iomap_read_folio_iter(&iter, &ctx,
+ &cur_folio_owned);

iomap_bio_submit_read(&ctx);

- if (!ctx.cur_folio_in_bio)
+ if (!cur_folio_owned)
folio_unlock(folio);

/*
@@ -494,12 +499,13 @@ int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
EXPORT_SYMBOL_GPL(iomap_read_folio);

static int iomap_readahead_iter(struct iomap_iter *iter,
- struct iomap_read_folio_ctx *ctx)
+ struct iomap_read_folio_ctx *ctx,
+ bool *cur_folio_owned)
{
int ret;

while (iomap_length(iter)) {
- if (ctx->cur_folio && !ctx->cur_folio_in_bio)
+ if (ctx->cur_folio && !*cur_folio_owned)
folio_unlock(ctx->cur_folio);
ctx->cur_folio = readahead_folio(ctx->rac);
/*
@@ -508,8 +514,8 @@ static int iomap_readahead_iter(struct iomap_iter *iter,
*/
if (WARN_ON_ONCE(!ctx->cur_folio))
return -EINVAL;
- ctx->cur_folio_in_bio = false;
- ret = iomap_read_folio_iter(iter, ctx);
+ *cur_folio_owned = false;
+ ret = iomap_read_folio_iter(iter, ctx, cur_folio_owned);
if (ret)
return ret;
}
@@ -542,15 +548,21 @@ void iomap_readahead(struct readahead_control *rac, const struct iomap_ops *ops)
struct iomap_read_folio_ctx ctx = {
.rac = rac,
};
+ /*
+ * If an external IO helper takes ownership of the folio, it is
+ * responsible for unlocking it when the read completes.
+ */
+ bool cur_folio_owned = false;

trace_iomap_readahead(rac->mapping->host, readahead_count(rac));

while (iomap_iter(&iter, ops) > 0)
- iter.status = iomap_readahead_iter(&iter, &ctx);
+ iter.status = iomap_readahead_iter(&iter, &ctx,
+ &cur_folio_owned);

iomap_bio_submit_read(&ctx);

- if (ctx.cur_folio && !ctx.cur_folio_in_bio)
+ if (ctx.cur_folio && !cur_folio_owned)
folio_unlock(ctx.cur_folio);
}
EXPORT_SYMBOL_GPL(iomap_readahead);
--
2.47.3