[PATCHSET 0/2] Shrink io_mapped_ubuf size

[PATCHSET 0/2] Shrink io_mapped_ubuf size

[Jens Axboe]

Hi,

This shrinks it from (now) 48 bytes to 32 bytes. No ill effects observed
in terms of performance.

-- 
Jens Axboe

[PATCH 1/2] io_uring/rsrc: get rid of io_mapped_ubuf->folio_mask

[Jens Axboe]

We don't really need to cache this, let's reclaim 8 bytes from struct
io_mapped_ubuf and just calculate it when we need it. The only hot path
here is io_import_fixed().

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/rsrc.c | 9 +++------
 io_uring/rsrc.h | 1 -
 2 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 9264e555ae59..2477995e2d65 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -988,13 +988,10 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
 	imu->ubuf_end = imu->ubuf + iov->iov_len;
 	imu->nr_bvecs = nr_pages;
 	imu->folio_shift = PAGE_SHIFT;
-	imu->folio_mask = PAGE_MASK;
-	if (coalesced) {
+	if (coalesced)
 		imu->folio_shift = data.folio_shift;
-		imu->folio_mask = ~((1UL << data.folio_shift) - 1);
-	}
 	refcount_set(&imu->refs, 1);
-	off = (unsigned long) iov->iov_base & ~imu->folio_mask;
+	off = (unsigned long) iov->iov_base & ((1UL << imu->folio_shift) - 1);
 	*pimu = imu;
 	ret = 0;
 
@@ -1132,7 +1129,7 @@ int io_import_fixed(int ddir, struct iov_iter *iter,
 			iter->bvec = bvec + seg_skip;
 			iter->nr_segs -= seg_skip;
 			iter->count -= bvec->bv_len + offset;
-			iter->iov_offset = offset & ~imu->folio_mask;
+			iter->iov_offset = offset & ((1UL << imu->folio_shift) - 1);
 		}
 	}
 
diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h
index eb4803e473b0..e290d2be3285 100644
--- a/io_uring/rsrc.h
+++ b/io_uring/rsrc.h
@@ -46,7 +46,6 @@ struct io_mapped_ubuf {
 	unsigned int	nr_bvecs;
 	unsigned int    folio_shift;
 	unsigned long	acct_pages;
-	unsigned long   folio_mask;
 	refcount_t	refs;
 	struct bio_vec	bvec[] __counted_by(nr_bvecs);
 };
-- 
2.45.2

[PATCH 2/2] io_uring/rsrc: change ubuf->ubuf_end to length tracking

[Jens Axboe]

If we change it to tracking ubuf->start + ubuf->len, then we can reduce
the size of struct io_mapped_ubuf by another 4 bytes, effectively 8
bytes, as a hole is eliminated too.

This shrinks io_mapped_ubuf to 32 bytes.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/fdinfo.c | 3 +--
 io_uring/rsrc.c   | 6 +++---
 io_uring/rsrc.h   | 4 ++--
 3 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/io_uring/fdinfo.c b/io_uring/fdinfo.c
index d43e1b5fcb36..6b1247664b35 100644
--- a/io_uring/fdinfo.c
+++ b/io_uring/fdinfo.c
@@ -177,9 +177,8 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file)
 	seq_printf(m, "UserBufs:\t%u\n", ctx->nr_user_bufs);
 	for (i = 0; has_lock && i < ctx->nr_user_bufs; i++) {
 		struct io_mapped_ubuf *buf = ctx->user_bufs[i];
-		unsigned int len = buf->ubuf_end - buf->ubuf;
 
-		seq_printf(m, "%5u: 0x%llx/%u\n", i, buf->ubuf, len);
+		seq_printf(m, "%5u: 0x%llx/%u\n", i, buf->ubuf, buf->len);
 	}
 	if (has_lock && !xa_empty(&ctx->personalities)) {
 		unsigned long index;
diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 2477995e2d65..131bcdda577a 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -38,7 +38,7 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
 static const struct io_mapped_ubuf dummy_ubuf = {
 	/* set invalid range, so io_import_fixed() fails meeting it */
 	.ubuf = -1UL,
-	.ubuf_end = 0,
+	.len = UINT_MAX,
 };
 
 int __io_account_mem(struct user_struct *user, unsigned long nr_pages)
@@ -985,7 +985,7 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
 	size = iov->iov_len;
 	/* store original address for later verification */
 	imu->ubuf = (unsigned long) iov->iov_base;
-	imu->ubuf_end = imu->ubuf + iov->iov_len;
+	imu->len = iov->iov_len;
 	imu->nr_bvecs = nr_pages;
 	imu->folio_shift = PAGE_SHIFT;
 	if (coalesced)
@@ -1086,7 +1086,7 @@ int io_import_fixed(int ddir, struct iov_iter *iter,
 	if (unlikely(check_add_overflow(buf_addr, (u64)len, &buf_end)))
 		return -EFAULT;
 	/* not inside the mapped region */
-	if (unlikely(buf_addr < imu->ubuf || buf_end > imu->ubuf_end))
+	if (unlikely(buf_addr < imu->ubuf || buf_end > (imu->ubuf + imu->len)))
 		return -EFAULT;
 
 	/*
diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h
index e290d2be3285..8ed588036210 100644
--- a/io_uring/rsrc.h
+++ b/io_uring/rsrc.h
@@ -42,11 +42,11 @@ struct io_rsrc_node {
 
 struct io_mapped_ubuf {
 	u64		ubuf;
-	u64		ubuf_end;
+	unsigned int	len;
 	unsigned int	nr_bvecs;
 	unsigned int    folio_shift;
-	unsigned long	acct_pages;
 	refcount_t	refs;
+	unsigned long	acct_pages;
 	struct bio_vec	bvec[] __counted_by(nr_bvecs);
 };
 
-- 
2.45.2

Re: [PATCHSET 0/2] Shrink io_mapped_ubuf size

[Kanchan Joshi]

On 9/15/2024 8:52 PM, Jens Axboe wrote:
> Hi,
> 
> This shrinks it from (now) 48 bytes to 32 bytes. No ill effects observed
> in terms of performance.

Reviewed-by: Kanchan Joshi <joshi.k@samsung.com>