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Xu Yang 4e527d5841 iomap: fault in smaller chunks for non-large folio mappings 
Since commit (5d8edfb900 "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: 5d8edfb900 ("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>
History 2024-05-24 13:34:07 +02:00
arch asm-generic cleanups for 6.10 2024-05-20 15:18:34 -07:00
block Mainly singleton patches, documented in their respective changelogs. 2024-05-19 14:02:03 -07:00
certs kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
crypto This push fixes a bug in the new ecc P521 code as well as a buggy 2024-05-20 08:47:54 -07:00
Documentation soc: devicetree updates for v6.10, part 2 2024-05-20 15:11:53 -07:00
drivers asm-generic cleanups for 6.10 2024-05-20 15:18:34 -07:00
fs iomap: fault in smaller chunks for non-large folio mappings 2024-05-24 13:34:07 +02:00
include filemap: add helper mapping_max_folio_size() 2024-05-24 13:34:06 +02:00
init Mainly singleton patches, documented in their respective changelogs. 2024-05-19 14:02:03 -07:00
io_uring The usual shower of singleton fixes and minor series all over MM, 2024-05-19 09:21:03 -07:00
ipc Mainly singleton patches, documented in their respective changelogs. 2024-05-19 14:02:03 -07:00
kernel VFIO updates for v6.10-rc1 2024-05-20 14:56:50 -07:00
lib Mainly singleton patches, documented in their respective changelogs. 2024-05-19 14:02:03 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm Mainly singleton patches, documented in their respective changelogs. 2024-05-19 14:02:03 -07:00
net dma-mapping updates for Linux 6.10 2024-05-20 10:23:39 -07:00
rust The usual shower of singleton fixes and minor series all over MM, 2024-05-19 09:21:03 -07:00
samples Mainly singleton patches, documented in their respective changelogs. 2024-05-19 14:02:03 -07:00
scripts Coccinelle commits for 6.10 2024-05-20 16:00:04 -07:00
security The usual shower of singleton fixes and minor series all over MM, 2024-05-19 09:21:03 -07:00
sound The usual shower of singleton fixes and minor series all over MM, 2024-05-19 09:21:03 -07:00
tools asm-generic cleanups for 6.10 2024-05-20 15:18:34 -07:00
usr kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
virt The usual shower of singleton fixes and minor series all over MM, 2024-05-19 09:21:03 -07:00
.clang-format clang-format: Update with v6.7-rc4's for_each macro list 2023-12-08 23:54:38 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig Add .editorconfig file for basic formatting 2023-12-28 16:22:47 +09:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: create a list of all built DTB files 2024-02-19 18:20:39 +09:00
.mailmap Another not-too-busy cycle for documentation, including: 2024-05-13 10:51:53 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Drop Gustavo Pimentel as PCI DWC Maintainer 2024-03-27 13:41:02 -05:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS VFIO updates for v6.10-rc1 2024-05-20 14:56:50 -07:00
Makefile Kbuild updates for v6.10 2024-05-18 12:39:20 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.