[PATCH V9 3/7] io_uring: shrink io_mapped_buf

[Ming Lei <ming.lei@redhat.com>]

`struct io_mapped_buf` will be extended to cover kernel buffer which
may be in fast IO path, and `struct io_mapped_buf` needs to be per-IO.

So shrink sizeof(struct io_mapped_buf) by the following ways:

- folio_shift is < 64, so 6bits are enough to hold it, the remained bits
  can be used for the coming kernel buffer

- define `acct_pages` as 'unsigned int', which is big enough for
  accounting pages in the buffer

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 io_uring/rsrc.c | 2 ++
 io_uring/rsrc.h | 6 +++---
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 9b8827c72230..16f5abe03d10 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -685,6 +685,8 @@ static bool io_try_coalesce_buffer(struct page ***pages, int *nr_pages,
 		return false;
 
 	data->folio_shift = folio_shift(folio);
+	WARN_ON_ONCE(data->folio_shift >= 64);
+
 	/*
 	 * Check if pages are contiguous inside a folio, and all folios have
 	 * the same page count except for the head and tail.
diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h
index 887699400e29..255ec94ea172 100644
--- a/io_uring/rsrc.h
+++ b/io_uring/rsrc.h
@@ -30,9 +30,9 @@ struct io_mapped_buf {
 	u64		start;
 	unsigned int	len;
 	unsigned int	nr_bvecs;
-	unsigned int    folio_shift;
 	refcount_t	refs;
-	unsigned long	acct_pages;
+	unsigned int	acct_pages;
+	unsigned int	folio_shift:6;
 	struct bio_vec	bvec[] __counted_by(nr_bvecs);
 };
 
@@ -41,7 +41,7 @@ struct io_imu_folio_data {
 	unsigned int	nr_pages_head;
 	/* For non-head/tail folios, has to be fully included */
 	unsigned int	nr_pages_mid;
-	unsigned int	folio_shift;
+	unsigned char	folio_shift;
 };
 
 struct io_rsrc_node *io_rsrc_node_alloc(struct io_ring_ctx *ctx, int type);
-- 
2.47.0