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Huang Ying b735a3e81b arm64, mm: avoid always making PTE dirty in pte_mkwrite()
[ Upstream commit 143937ca51cc6ae2fccc61a1cb916abb24cd34f5 ]

Current pte_mkwrite_novma() makes PTE dirty unconditionally.  This may
mark some pages that are never written dirty wrongly.  For example,
do_swap_page() may map the exclusive pages with writable and clean PTEs
if the VMA is writable and the page fault is for read access.
However, current pte_mkwrite_novma() implementation always dirties the
PTE.  This may cause unnecessary disk writing if the pages are
never written before being reclaimed.

So, change pte_mkwrite_novma() to clear the PTE_RDONLY bit only if the
PTE_DIRTY bit is set to make it possible to make the PTE writable and
clean.

The current behavior was introduced in commit 73e86cb03c ("arm64:
Move PTE_RDONLY bit handling out of set_pte_at()").  Before that,
pte_mkwrite() only sets the PTE_WRITE bit, while set_pte_at() only
clears the PTE_RDONLY bit if both the PTE_WRITE and the PTE_DIRTY bits
are set.

To test the performance impact of the patch, on an arm64 server
machine, run 16 redis-server processes on socket 1 and 16
memtier_benchmark processes on socket 0 with mostly get
transactions (that is, redis-server will mostly read memory only).
The memory footprint of redis-server is larger than the available
memory, so swap out/in will be triggered.  Test results show that the
patch can avoid most swapping out because the pages are mostly clean.
And the benchmark throughput improves ~23.9% in the test.

Fixes: 73e86cb03c ("arm64: Move PTE_RDONLY bit handling out of set_pte_at()")
Signed-off-by: Huang Ying <ying.huang@linux.alibaba.com>
Cc: Will Deacon <will@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Gavin Shan <gshan@redhat.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Yicong Yang <yangyicong@hisilicon.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2025-10-29 13:59:59 +01:00
arch arm64, mm: avoid always making PTE dirty in pte_mkwrite() 2025-10-29 13:59:59 +01:00
block block: use int to store blk_stack_limits() return value 2025-10-29 13:59:46 +01:00
certs
crypto crypto: essiv - Check ssize for decryption and in-place encryption 2025-10-29 13:59:52 +01:00
Documentation fs: Add 'initramfs_options' to set initramfs mount options 2025-10-29 13:59:55 +01:00
drivers net: enetc: correct the value of ENETC_RXB_TRUESIZE 2025-10-29 13:59:59 +01:00
fs hfsplus: return EIO when type of hidden directory mismatch in hfsplus_fill_super() 2025-10-29 13:59:58 +01:00
include net: add ndo_fdb_del_bulk 2025-10-29 13:59:59 +01:00
init bpfilter: match bit size of bpfilter_umh to that of the kernel 2025-07-17 18:24:51 +02:00
ipc
kernel sched/fair: Fix pelt lost idle time detection 2025-10-29 13:59:57 +01:00
lib lib/genalloc: fix device leak in of_gen_pool_get() 2025-10-29 13:59:53 +01:00
LICENSES
mm mm: hugetlb: avoid soft lockup when mprotect to large memory area 2025-10-29 13:59:50 +01:00
net rtnetlink: Allow deleting FDB entries in user namespace 2025-10-29 13:59:59 +01:00
samples samples: mei: Fix building on musl libc 2025-08-28 16:21:19 +02:00
scripts randstruct: gcc-plugin: Fix attribute addition 2025-09-09 18:44:01 +02:00
security securityfs: don't pin dentries twice, once is enough... 2025-08-28 16:21:24 +02:00
sound ALSA: firewire: amdtp-stream: fix enum kernel-doc warnings 2025-10-29 13:59:57 +01:00
tools rseq/selftests: Use weak symbol reference, not definition, to link with glibc 2025-10-29 13:59:54 +01:00
usr kbuild: hdrcheck: fix cross build with clang 2025-07-17 18:24:51 +02:00
virt
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS platform: Add Surface platform directory 2025-06-27 11:02:56 +01:00
Makefile Linux 5.4.300 2025-10-02 13:34:35 +02:00
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 Restructured Text 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.