6.6-stable review patch. If anyone has any objections, please let me know.
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From: Xu Yang xu.yang_2@nxp.com
commit 4e527d5841e24623181edc7fd6f6598ffa810e10 upstream.
Since commit (5d8edfb900d5 "iomap: Copy larger chunks from userspace"), iomap will try to copy in larger chunks than PAGE_SIZE. However, if the mapping doesn't support large folio, only one page of maximum 4KB will be created and 4KB data will be writen to pagecache each time. Then, next 4KB will be handled in next iteration. This will cause potential write performance problem.
If chunk is 2MB, total 512 pages need to be handled finally. During this period, fault_in_iov_iter_readable() is called to check iov_iter readable validity. Since only 4KB will be handled each time, below address space will be checked over and over again:
start end - buf, buf+2MB buf+4KB, buf+2MB buf+8KB, buf+2MB ... buf+2044KB buf+2MB
Obviously the checking size is wrong since only 4KB will be handled each time. So this will get a correct chunk to let iomap work well in non-large folio case.
With this change, the write speed will be stable. Tested on ARM64 device.
Before:
- dd if=/dev/zero of=/dev/sda bs=400K count=10485 (334 MB/s) - dd if=/dev/zero of=/dev/sda bs=800K count=5242 (278 MB/s) - dd if=/dev/zero of=/dev/sda bs=1600K count=2621 (204 MB/s) - dd if=/dev/zero of=/dev/sda bs=2200K count=1906 (170 MB/s) - dd if=/dev/zero of=/dev/sda bs=3000K count=1398 (150 MB/s) - dd if=/dev/zero of=/dev/sda bs=4500K count=932 (139 MB/s)
After:
- dd if=/dev/zero of=/dev/sda bs=400K count=10485 (339 MB/s) - dd if=/dev/zero of=/dev/sda bs=800K count=5242 (330 MB/s) - dd if=/dev/zero of=/dev/sda bs=1600K count=2621 (332 MB/s) - dd if=/dev/zero of=/dev/sda bs=2200K count=1906 (333 MB/s) - dd if=/dev/zero of=/dev/sda bs=3000K count=1398 (333 MB/s) - dd if=/dev/zero of=/dev/sda bs=4500K count=932 (333 MB/s)
Fixes: 5d8edfb900d5 ("iomap: Copy larger chunks from userspace") Cc: stable@vger.kernel.org Reviewed-by: Darrick J. Wong djwong@kernel.org Signed-off-by: Xu Yang xu.yang_2@nxp.com Link: https://lore.kernel.org/r/20240521114939.2541461-2-xu.yang_2@nxp.com Reviewed-by: Christoph Hellwig hch@lst.de Reviewed-by: Matthew Wilcox (Oracle) willy@infradead.org Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/iomap/buffered-io.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -868,11 +868,11 @@ static size_t iomap_write_end(struct iom static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i) { loff_t length = iomap_length(iter); - size_t chunk = PAGE_SIZE << MAX_PAGECACHE_ORDER; loff_t pos = iter->pos; ssize_t written = 0; long status = 0; struct address_space *mapping = iter->inode->i_mapping; + size_t chunk = mapping_max_folio_size(mapping); unsigned int bdp_flags = (iter->flags & IOMAP_NOWAIT) ? BDP_ASYNC : 0;
do {