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Message-Id: <20251011013312.20698-1-changfengnan@bytedance.com>
Date: Sat, 11 Oct 2025 09:33:12 +0800
From: Fengnan Chang <changfengnan@...edance.com>
To: axboe@...nel.dk,
viro@...iv.linux.org.uk,
brauner@...nel.org,
jack@...e.cz,
asml.silence@...il.com,
willy@...radead.org,
djwong@...nel.org,
hch@...radead.org,
ritesh.list@...il.com,
linux-fsdevel@...r.kernel.org,
io-uring@...r.kernel.org,
linux-xfs@...r.kernel.org,
linux-ext4@...r.kernel.org
Cc: Fengnan Chang <changfengnan@...edance.com>
Subject: [PATCH] block: enable per-cpu bio cache by default
Per cpu bio cache was only used in the io_uring + raw block device,
after commit 12e4e8c7ab59 ("io_uring/rw: enable bio caches for IRQ
rw"), bio_put is safe for task and irq context, bio_alloc_bioset is
safe for task context and no one calls in irq context, so we can enable
per cpu bio cache by default.
Benchmarked with t/io_uring and ext4+nvme:
taskset -c 6 /root/fio/t/io_uring -p0 -d128 -b4096 -s1 -c1 -F1 -B1 -R1
-X1 -n1 -P1 /mnt/testfile
base IOPS is 562K, patch IOPS is 574K. The CPU usage of bio_alloc_bioset
decrease from 1.42% to 1.22%.
The worst case is allocate bio in CPU A but free in CPU B, still use
t/io_uring and ext4+nvme:
base IOPS is 648K, patch IOPS is 647K.
Also use fio test ext4/xfs with libaio/sync/io_uring on null_blk and
nvme, no obvious performance regression.
Signed-off-by: Fengnan Chang <changfengnan@...edance.com>
---
block/bio.c | 26 ++++++++++++--------------
block/blk-map.c | 4 ++++
block/fops.c | 4 ----
include/linux/fs.h | 3 ---
io_uring/rw.c | 1 -
5 files changed, 16 insertions(+), 22 deletions(-)
diff --git a/block/bio.c b/block/bio.c
index 3b371a5da159..16b20c10cab7 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -513,20 +513,18 @@ struct bio *bio_alloc_bioset(struct block_device *bdev, unsigned short nr_vecs,
if (WARN_ON_ONCE(!mempool_initialized(&bs->bvec_pool) && nr_vecs > 0))
return NULL;
- if (opf & REQ_ALLOC_CACHE) {
- if (bs->cache && nr_vecs <= BIO_INLINE_VECS) {
- bio = bio_alloc_percpu_cache(bdev, nr_vecs, opf,
- gfp_mask, bs);
- if (bio)
- return bio;
- /*
- * No cached bio available, bio returned below marked with
- * REQ_ALLOC_CACHE to particpate in per-cpu alloc cache.
- */
- } else {
- opf &= ~REQ_ALLOC_CACHE;
- }
- }
+ opf |= REQ_ALLOC_CACHE;
+ if (bs->cache && nr_vecs <= BIO_INLINE_VECS) {
+ bio = bio_alloc_percpu_cache(bdev, nr_vecs, opf,
+ gfp_mask, bs);
+ if (bio)
+ return bio;
+ /*
+ * No cached bio available, bio returned below marked with
+ * REQ_ALLOC_CACHE to participate in per-cpu alloc cache.
+ */
+ } else
+ opf &= ~REQ_ALLOC_CACHE;
/*
* submit_bio_noacct() converts recursion to iteration; this means if
diff --git a/block/blk-map.c b/block/blk-map.c
index 23e5d5ebe59e..570a7ca6edd1 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -255,6 +255,10 @@ static struct bio *blk_rq_map_bio_alloc(struct request *rq,
{
struct bio *bio;
+ /*
+ * Even REQ_ALLOC_CACHE is enabled by default, we still need this to
+ * mark bio is allocated by bio_alloc_bioset.
+ */
if (rq->cmd_flags & REQ_ALLOC_CACHE && (nr_vecs <= BIO_INLINE_VECS)) {
bio = bio_alloc_bioset(NULL, nr_vecs, rq->cmd_flags, gfp_mask,
&fs_bio_set);
diff --git a/block/fops.c b/block/fops.c
index ddbc69c0922b..090562a91b4c 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -177,8 +177,6 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
loff_t pos = iocb->ki_pos;
int ret = 0;
- if (iocb->ki_flags & IOCB_ALLOC_CACHE)
- opf |= REQ_ALLOC_CACHE;
bio = bio_alloc_bioset(bdev, nr_pages, opf, GFP_KERNEL,
&blkdev_dio_pool);
dio = container_of(bio, struct blkdev_dio, bio);
@@ -326,8 +324,6 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
loff_t pos = iocb->ki_pos;
int ret = 0;
- if (iocb->ki_flags & IOCB_ALLOC_CACHE)
- opf |= REQ_ALLOC_CACHE;
bio = bio_alloc_bioset(bdev, nr_pages, opf, GFP_KERNEL,
&blkdev_dio_pool);
dio = container_of(bio, struct blkdev_dio, bio);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 601d036a6c78..18ec41732186 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -365,8 +365,6 @@ struct readahead_control;
/* iocb->ki_waitq is valid */
#define IOCB_WAITQ (1 << 19)
#define IOCB_NOIO (1 << 20)
-/* can use bio alloc cache */
-#define IOCB_ALLOC_CACHE (1 << 21)
/*
* IOCB_DIO_CALLER_COMP can be set by the iocb owner, to indicate that the
* iocb completion can be passed back to the owner for execution from a safe
@@ -399,7 +397,6 @@ struct readahead_control;
{ IOCB_WRITE, "WRITE" }, \
{ IOCB_WAITQ, "WAITQ" }, \
{ IOCB_NOIO, "NOIO" }, \
- { IOCB_ALLOC_CACHE, "ALLOC_CACHE" }, \
{ IOCB_DIO_CALLER_COMP, "CALLER_COMP" }, \
{ IOCB_AIO_RW, "AIO_RW" }, \
{ IOCB_HAS_METADATA, "AIO_HAS_METADATA" }
diff --git a/io_uring/rw.c b/io_uring/rw.c
index af5a54b5db12..fa7655ab9097 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -856,7 +856,6 @@ static int io_rw_init_file(struct io_kiocb *req, fmode_t mode, int rw_type)
ret = kiocb_set_rw_flags(kiocb, rw->flags, rw_type);
if (unlikely(ret))
return ret;
- kiocb->ki_flags |= IOCB_ALLOC_CACHE;
/*
* If the file is marked O_NONBLOCK, still allow retry for it if it
--
2.39.5 (Apple Git-154)
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