From: Zi Yan <ziy(a)nvidia.com>
Hi all,
File folio supports any order and people would like to support flexible orders
for anonymous folio[1] too. Currently, split_huge_page() only splits a huge
page to order-0 pages, but splitting to orders higher than 0 is also useful.
This patchset adds support for splitting a huge page to any lower order pages
and uses it during file folio truncate operations.
The patchset is on top of mm-everything-2023-03-27-21-20.
Changelog
===
Since v2
---
1. Fixed an issue in __split_page_owner() introduced during my rebase
Since v1
---
1. Changed split_page_memcg() and split_page_owner() parameter to use order
2. Used folio_test_pmd_mappable() in place of the equivalent code
Details
===
* Patch 1 changes split_page_memcg() to use order instead of nr_pages
* Patch 2 changes split_page_owner() to use order instead of nr_pages
* Patch 3 and 4 add new_order parameter split_page_memcg() and
split_page_owner() and prepare for upcoming changes.
* Patch 5 adds split_huge_page_to_list_to_order() to split a huge page
to any lower order. The original split_huge_page_to_list() calls
split_huge_page_to_list_to_order() with new_order = 0.
* Patch 6 uses split_huge_page_to_list_to_order() in large pagecache folio
truncation instead of split the large folio all the way down to order-0.
* Patch 7 adds a test API to debugfs and test cases in
split_huge_page_test selftests.
Comments and/or suggestions are welcome.
[1] https://lore.kernel.org/linux-mm/Y%2FblF0GIunm+pRIC@casper.infradead.org/
Zi Yan (7):
mm/memcg: use order instead of nr in split_page_memcg()
mm/page_owner: use order instead of nr in split_page_owner()
mm: memcg: make memcg huge page split support any order split.
mm: page_owner: add support for splitting to any order in split
page_owner.
mm: thp: split huge page to any lower order pages.
mm: truncate: split huge page cache page to a non-zero order if
possible.
mm: huge_memory: enable debugfs to split huge pages to any order.
include/linux/huge_mm.h | 10 +-
include/linux/memcontrol.h | 4 +-
include/linux/page_owner.h | 10 +-
mm/huge_memory.c | 137 ++++++++---
mm/memcontrol.c | 10 +-
mm/page_alloc.c | 8 +-
mm/page_owner.c | 8 +-
mm/truncate.c | 21 +-
.../selftests/mm/split_huge_page_test.c | 225 +++++++++++++++++-
9 files changed, 365 insertions(+), 68 deletions(-)
--
2.39.2
Make sv48 the default address space for mmap as some applications
currently depend on this assumption. Users can now select a
desired address space using a non-zero hint address to mmap. Previously,
requesting the default address space from mmap by passing zero as the hint
address would result in using the largest address space possible. Some
applications depend on empty bits in the virtual address space, like Go and
Java, so this patch provides more flexibility for application developers.
-Charlie
---
v10:
- Move pgtable.h defintions into a no __ASSEMBLY__ region to resolve compilation
conflicts (pointed out by Conor)
- Will now compile with allmodconfig
v9:
- Raise the mmap_end default to STACK_TOP_MAX to allow the address space to grow
beyond the default of sv48 on sv57 machines as suggested by Alexandre
- Some of the mmap macros had unnecessary conditionals that I have removed
v8:
- Fix RV32 and the RV32 compat mode of RV64 (suggested by Conor)
- Extract out addr and base from the mmap macros (suggested by Alexandre)
v7:
- Changing RLIMIT_STACK inside of an executing program does not trigger
arch_pick_mmap_layout(), so rewrite tests to change RLIMIT_STACK from a
script before executing tests. RLIMIT_STACK of infinity forces bottomup
mmap allocation.
- Make arch_get_mmap_base macro more readible by extracting out the rnd
calculation.
- Use MMAP_MIN_VA_BITS in TASK_UNMAPPED_BASE to support case when mmap
attempts to allocate address smaller than DEFAULT_MAP_WINDOW.
- Fix incorrect wording in documentation.
v6:
- Rebase onto the correct base
v5:
- Minor wording change in documentation
- Change some parenthesis in arch_get_mmap_ macros
- Added case for addr==0 in arch_get_mmap_ because without this, programs would
crash if RLIMIT_STACK was modified before executing the program. This was
tested using the libhugetlbfs tests.
v4:
- Split testcases/document patch into test cases, in-code documentation, and
formal documentation patches
- Modified the mmap_base macro to be more legible and better represent memory
layout
- Fixed documentation to better reflect the implmentation
- Renamed DEFAULT_VA_BITS to MMAP_VA_BITS
- Added additional test case for rlimit changes
---
Charlie Jenkins (4):
RISC-V: mm: Restrict address space for sv39,sv48,sv57
RISC-V: mm: Add tests for RISC-V mm
RISC-V: mm: Update pgtable comment documentation
RISC-V: mm: Document mmap changes
Documentation/riscv/vm-layout.rst | 22 +++++++
arch/riscv/include/asm/elf.h | 2 +-
arch/riscv/include/asm/pgtable.h | 33 ++++++++--
arch/riscv/include/asm/processor.h | 52 +++++++++++++--
tools/testing/selftests/riscv/Makefile | 2 +-
tools/testing/selftests/riscv/mm/.gitignore | 2 +
tools/testing/selftests/riscv/mm/Makefile | 15 +++++
.../riscv/mm/testcases/mmap_bottomup.c | 35 ++++++++++
.../riscv/mm/testcases/mmap_default.c | 35 ++++++++++
.../selftests/riscv/mm/testcases/mmap_test.h | 64 +++++++++++++++++++
.../selftests/riscv/mm/testcases/run_mmap.sh | 12 ++++
11 files changed, 261 insertions(+), 13 deletions(-)
create mode 100644 tools/testing/selftests/riscv/mm/.gitignore
create mode 100644 tools/testing/selftests/riscv/mm/Makefile
create mode 100644 tools/testing/selftests/riscv/mm/testcases/mmap_bottomup.c
create mode 100644 tools/testing/selftests/riscv/mm/testcases/mmap_default.c
create mode 100644 tools/testing/selftests/riscv/mm/testcases/mmap_test.h
create mode 100755 tools/testing/selftests/riscv/mm/testcases/run_mmap.sh
--
2.34.1
Hi,
Changes since v2 [1]:
* Added a new patch (sent separately earlier) at the end, to error out
if "make headers" has not yet been run.
* Reworked and simplified the uffd movement patch. Now it only moves
some uffd*() routines, not all, and doesn't have to touch the Makefile
at all. This lighter touch also allowed me to drop the "move psize(),
pshift() into vm_utils.c" entirely. I expect Peter Xu will be a little
happier with this new approach.
* Fixed the commit description for the MADV_COLLAPSE patch.
* Added more Reviewed-by tags from David Hildenbrand and Peter Xu.
[1] https://lore.kernel.org/all/20230603021558.95299-1-jhubbard@nvidia.com/
John Hubbard (11):
selftests/mm: fix uffd-stress unused function warning
selftests/mm: fix unused variable warnings in hugetlb-madvise.c,
migration.c
selftests/mm: fix "warning: expression which evaluates to zero..." in
mlock2-tests.c
selftests/mm: fix invocation of tests that are run via shell scripts
selftests/mm: .gitignore: add mkdirty, va_high_addr_switch
selftests/mm: fix two -Wformat-security warnings in uffd builds
selftests/mm: fix a "possibly uninitialized" warning in pkey-x86.h
selftests/mm: fix build failures due to missing MADV_COLLAPSE
selftests/mm: move certain uffd*() routines from vm_util.c to
uffd-common.c
Documentation: kselftest: "make headers" is a prerequisite
selftests: error out if kernel header files are not yet built
Documentation/dev-tools/kselftest.rst | 1 +
tools/testing/selftests/lib.mk | 36 +++++++++++-
tools/testing/selftests/mm/.gitignore | 2 +
tools/testing/selftests/mm/cow.c | 7 ---
tools/testing/selftests/mm/hugetlb-madvise.c | 8 ++-
tools/testing/selftests/mm/khugepaged.c | 10 ----
tools/testing/selftests/mm/migration.c | 5 +-
tools/testing/selftests/mm/mlock2-tests.c | 1 -
tools/testing/selftests/mm/pkey-x86.h | 2 +-
tools/testing/selftests/mm/run_vmtests.sh | 6 +-
tools/testing/selftests/mm/uffd-common.c | 59 ++++++++++++++++++++
tools/testing/selftests/mm/uffd-common.h | 5 ++
tools/testing/selftests/mm/uffd-stress.c | 10 ----
tools/testing/selftests/mm/uffd-unit-tests.c | 16 ++----
tools/testing/selftests/mm/vm_util.c | 59 --------------------
tools/testing/selftests/mm/vm_util.h | 14 +++--
16 files changed, 130 insertions(+), 111 deletions(-)
base-commit: f8dba31b0a826e691949cd4fdfa5c30defaac8c5
--
2.40.1
Regressions that cause a device to no longer be probed by a driver can
have a big impact on the platform's functionality, and despite being
relatively common there isn't currently any generic test to detect them.
As an example, bootrr [1] does test for device probe, but it requires
defining the expected probed devices for each platform.
Given that the Devicetree already provides a static description of
devices on the system, it is a good basis for building such a test on
top.
This series introduces a test to catch regressions that prevent devices
from probing.
Patches 1 and 2 extend the existing dt-extract-compatibles to be able to
output only the compatibles that can be expected to match a Devicetree
node to a driver. Patch 2 adds a kselftest that walks over the
Devicetree nodes on the current platform and compares the compatibles to
the ones on the list, and on an ignore list, to point out devices that
failed to be probed.
A compatible list is needed because not all compatibles that can show up
in a Devicetree node can be used to match to a driver, for example the
code for that compatible might use "OF_DECLARE" type macros and avoid
the driver framework, or the node might be controlled by a driver that
was bound to a different node.
An ignore list is needed for the few cases where it's common for a
driver to match a device but not probe, like for the "simple-mfd"
compatible, where the driver only probes if that compatible is the
node's first compatible.
The reason for parsing the kernel source instead of relying on
information exposed by the kernel at runtime (say, looking at modaliases
or introducing some other mechanism), is to be able to catch issues
where a config was renamed or a driver moved across configs, and the
.config used by the kernel not updated accordingly. We need to parse the
source to find all compatibles present in the kernel independent of the
current config being run.
[1] https://github.com/kernelci/bootrr
Changes in v3:
- Added DT selftest path to MAINTAINERS
- Enabled device probe test for nodes with 'status = "ok"'
- Added pass/fail/skip totals to end of test output
Changes in v2:
- Extended dt-extract-compatibles script to be able to extract driver
matching compatibles, instead of adding a new one in Coccinelle
- Made kselftest output in the KTAP format
Nícolas F. R. A. Prado (3):
dt: dt-extract-compatibles: Handle cfile arguments in generator
function
dt: dt-extract-compatibles: Add flag for driver matching compatibles
kselftest: Add new test for detecting unprobed Devicetree devices
MAINTAINERS | 1 +
scripts/dtc/dt-extract-compatibles | 74 +++++++++++++----
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/dt/.gitignore | 1 +
tools/testing/selftests/dt/Makefile | 21 +++++
.../selftests/dt/compatible_ignore_list | 1 +
tools/testing/selftests/dt/ktap_helpers.sh | 70 ++++++++++++++++
.../selftests/dt/test_unprobed_devices.sh | 83 +++++++++++++++++++
8 files changed, 236 insertions(+), 16 deletions(-)
create mode 100644 tools/testing/selftests/dt/.gitignore
create mode 100644 tools/testing/selftests/dt/Makefile
create mode 100644 tools/testing/selftests/dt/compatible_ignore_list
create mode 100644 tools/testing/selftests/dt/ktap_helpers.sh
create mode 100755 tools/testing/selftests/dt/test_unprobed_devices.sh
--
2.42.0
Hi Reinette, Fenghua,
This series introduces a new mount option enabling an alternate mode for
MBM to work around an issue on present AMD implementations and any other
resctrl implementation where there are more RMIDs (or equivalent) than
hardware counters.
The L3 External Bandwidth Monitoring feature of the AMD PQoS
extension[1] only guarantees that RMIDs currently assigned to a
processor will be tracked by hardware. The counters of any other RMIDs
which are no longer being tracked will be reset to zero. The MBM event
counters return "Unavailable" to indicate when this has happened.
An interval for effectively measuring memory bandwidth typically needs
to be multiple seconds long. In Google's workloads, it is not feasible
to bound the number of jobs with different RMIDs which will run in a
cache domain over any period of time. Consequently, on a
fully-committed system where all RMIDs are allocated, few groups'
counters return non-zero values.
To demonstrate the underlying issue, the first patch provides a test
case in tools/testing/selftests/resctrl/test_rmids.sh.
On an AMD EPYC 7B12 64-Core Processor with the default behavior:
# ./test_rmids.sh
Created 255 monitoring groups.
g1: mbm_total_bytes: Unavailable -> Unavailable (FAIL)
g2: mbm_total_bytes: Unavailable -> Unavailable (FAIL)
g3: mbm_total_bytes: Unavailable -> Unavailable (FAIL)
[..]
g238: mbm_total_bytes: Unavailable -> Unavailable (FAIL)
g239: mbm_total_bytes: Unavailable -> Unavailable (FAIL)
g240: mbm_total_bytes: Unavailable -> Unavailable (FAIL)
g241: mbm_total_bytes: Unavailable -> 660497472
g242: mbm_total_bytes: Unavailable -> 660793344
g243: mbm_total_bytes: Unavailable -> 660477312
g244: mbm_total_bytes: Unavailable -> 660495360
g245: mbm_total_bytes: Unavailable -> 660775360
g246: mbm_total_bytes: Unavailable -> 660645504
g247: mbm_total_bytes: Unavailable -> 660696128
g248: mbm_total_bytes: Unavailable -> 660605248
g249: mbm_total_bytes: Unavailable -> 660681280
g250: mbm_total_bytes: Unavailable -> 660834240
g251: mbm_total_bytes: Unavailable -> 660440064
g252: mbm_total_bytes: Unavailable -> 660501504
g253: mbm_total_bytes: Unavailable -> 660590720
g254: mbm_total_bytes: Unavailable -> 660548352
g255: mbm_total_bytes: Unavailable -> 660607296
255 groups, 0 returned counts in first pass, 15 in second
successfully measured bandwidth from 15/255 groups
To compare, here is the output from an Intel(R) Xeon(R) Platinum 8173M
CPU:
# ./test_rmids.sh
Created 223 monitoring groups.
g1: mbm_total_bytes: 0 -> 606126080
g2: mbm_total_bytes: 0 -> 613236736
g3: mbm_total_bytes: 0 -> 610254848
[..]
g221: mbm_total_bytes: 0 -> 584679424
g222: mbm_total_bytes: 0 -> 588808192
g223: mbm_total_bytes: 0 -> 587317248
223 groups, 223 returned counts in first pass, 223 in second
successfully measured bandwidth from 223/223 groups
To make better use of the hardware in such a use case, this patchset
introduces a "soft" RMID implementation, where each CPU is permanently
assigned a "hard" RMID. On context switches which change the current
soft RMID, the difference between each CPU's current event counts and
most recent counts is added to the totals for the current or outgoing
soft RMID.
This technique does not work for cache occupancy counters, so this patch
series disables cache occupancy events when soft RMIDs are enabled.
This series adds the "mbm_soft_rmid" mount option to allow users to
opt-in to the functionaltiy when they deem it helpful.
When the same system from the earlier AMD example enables the
mbm_soft_rmid mount option:
# ./test_rmids.sh
Created 255 monitoring groups.
g1: mbm_total_bytes: 0 -> 686560576
g2: mbm_total_bytes: 0 -> 668204416
[..]
g252: mbm_total_bytes: 0 -> 672651200
g253: mbm_total_bytes: 0 -> 666956800
g254: mbm_total_bytes: 0 -> 665917056
g255: mbm_total_bytes: 0 -> 671049600
255 groups, 255 returned counts in first pass, 255 in second
successfully measured bandwidth from 255/255 groups
(patches are based on tip/master)
[1] https://www.amd.com/system/files/TechDocs/56375_1.03_PUB.pdf
Peter Newman (8):
selftests/resctrl: Verify all RMIDs count together
x86/resctrl: Add resctrl_mbm_flush_cpu() to collect CPUs' MBM events
x86/resctrl: Flush MBM event counts on soft RMID change
x86/resctrl: Call mon_event_count() directly for soft RMIDs
x86/resctrl: Create soft RMID version of __mon_event_count()
x86/resctrl: Assign HW RMIDs to CPUs for soft RMID
x86/resctrl: Use mbm_update() to push soft RMID counts
x86/resctrl: Add mount option to enable soft RMID
Stephane Eranian (1):
x86/resctrl: Hold a spinlock in __rmid_read() on AMD
arch/x86/include/asm/resctrl.h | 29 +++-
arch/x86/kernel/cpu/resctrl/core.c | 80 ++++++++-
arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 9 +-
arch/x86/kernel/cpu/resctrl/internal.h | 19 ++-
arch/x86/kernel/cpu/resctrl/monitor.c | 158 +++++++++++++++++-
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 52 ++++++
tools/testing/selftests/resctrl/test_rmids.sh | 93 +++++++++++
7 files changed, 425 insertions(+), 15 deletions(-)
create mode 100755 tools/testing/selftests/resctrl/test_rmids.sh
base-commit: dd806e2f030e57dd5bac973372aa252b6c175b73
--
2.40.0.634.g4ca3ef3211-goog
Adds a check to verify if the rtc device file is valid or not
and prints a useful error message if the file is not accessible.
Signed-off-by: Atul Kumar Pant <atulpant.linux(a)gmail.com>
---
changes since v5:
Updated error message to use strerror().
If the rtc file is invalid, the skip the test.
changes since v4:
Updated the commit message.
changes since v3:
Added Linux-kselftest and Linux-kernel mailing lists.
changes since v2:
Changed error message when rtc file does not exist.
changes since v1:
Removed check for uid=0
If rtc file is invalid, then exit the test.
tools/testing/selftests/rtc/rtctest.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/rtc/rtctest.c b/tools/testing/selftests/rtc/rtctest.c
index 630fef735c7e..27b466111885 100644
--- a/tools/testing/selftests/rtc/rtctest.c
+++ b/tools/testing/selftests/rtc/rtctest.c
@@ -15,6 +15,7 @@
#include <sys/types.h>
#include <time.h>
#include <unistd.h>
+#include <error.h>
#include "../kselftest_harness.h"
#include "../kselftest.h"
@@ -437,7 +438,7 @@ int main(int argc, char **argv)
if (access(rtc_file, F_OK) == 0)
ret = test_harness_run(argc, argv);
else
- ksft_exit_fail_msg("[ERROR]: Cannot access rtc file %s - Exiting\n", rtc_file);
+ ksft_exit_skip("%s: %s\n", rtc_file, strerror(errno));
return ret;
}
--
2.25.1
*Changes in v33*:
- Add PAGE_IS_FILE support for THPs
*Changes in v31 and v32*:
- Minor updates
*Changes in v30*:
- Rebase on top of next-20230815
- Minor nitpicks
*Changes in v29:*
- Polish IOCTL and improve documentation
*Changes in v28:*
- Fix walk_end and add 17 test cases in selftests patch
*Changes in v27:*
- Handle review comments and minor improvements
- Add performance improvement patch on top with test for easy review
*Changes in v26:*
- Code re-structurring and API changes in PAGEMAP_IOCTL
*Changes in v25*:
- Do proper filtering on hole as well (hole got missed earlier)
*Changes in v24*:
- Rebase on top of next-20230710
- Place WP markers in case of hole as well
*Changes in v23*:
- Set vec_buf_index in loop only when vec_buf_index is set
- Return -EFAULT instead of -EINVAL if vec is NULL
- Correctly return the walk ending address to the page granularity
*Changes in v22*:
- Interface change:
- Replace [start start + len) with [start, end)
- Return the ending address of the address walk in start
*Changes in v21*:
- Abort walk instead of returning error if WP is to be performed on
partial hugetlb
*Changes in v20*
- Correct PAGE_IS_FILE and add PAGE_IS_PFNZERO
*Changes in v19*
- Minor changes and interface updates
*Changes in v18*
- Rebase on top of next-20230613
- Minor updates
*Changes in v17*
- Rebase on top of next-20230606
- Minor improvements in PAGEMAP_SCAN IOCTL patch
*Changes in v16*
- Fix a corner case
- Add exclusive PM_SCAN_OP_WP back
*Changes in v15*
- Build fix (Add missed build fix in RESEND)
*Changes in v14*
- Fix build error caused by #ifdef added at last minute in some configs
*Changes in v13*
- Rebase on top of next-20230414
- Give-up on using uffd_wp_range() and write new helpers, flush tlb only
once
*Changes in v12*
- Update and other memory types to UFFD_FEATURE_WP_ASYNC
- Rebaase on top of next-20230406
- Review updates
*Changes in v11*
- Rebase on top of next-20230307
- Base patches on UFFD_FEATURE_WP_UNPOPULATED
- Do a lot of cosmetic changes and review updates
- Remove ENGAGE_WP + !GET operation as it can be performed with
UFFDIO_WRITEPROTECT
*Changes in v10*
- Add specific condition to return error if hugetlb is used with wp
async
- Move changes in tools/include/uapi/linux/fs.h to separate patch
- Add documentation
*Changes in v9:*
- Correct fault resolution for userfaultfd wp async
- Fix build warnings and errors which were happening on some configs
- Simplify pagemap ioctl's code
*Changes in v8:*
- Update uffd async wp implementation
- Improve PAGEMAP_IOCTL implementation
*Changes in v7:*
- Add uffd wp async
- Update the IOCTL to use uffd under the hood instead of soft-dirty
flags
*Motivation*
The real motivation for adding PAGEMAP_SCAN IOCTL is to emulate Windows
GetWriteWatch() and ResetWriteWatch() syscalls [1]. The GetWriteWatch()
retrieves the addresses of the pages that are written to in a region of
virtual memory.
This syscall is used in Windows applications and games etc. This syscall is
being emulated in pretty slow manner in userspace. Our purpose is to
enhance the kernel such that we translate it efficiently in a better way.
Currently some out of tree hack patches are being used to efficiently
emulate it in some kernels. We intend to replace those with these patches.
So the whole gaming on Linux can effectively get benefit from this. It
means there would be tons of users of this code.
CRIU use case [2] was mentioned by Andrei and Danylo:
> Use cases for migrating sparse VMAs are binaries sanitized with ASAN,
> MSAN or TSAN [3]. All of these sanitizers produce sparse mappings of
> shadow memory [4]. Being able to migrate such binaries allows to highly
> reduce the amount of work needed to identify and fix post-migration
> crashes, which happen constantly.
Andrei's defines the following uses of this code:
* it is more granular and allows us to track changed pages more
effectively. The current interface can clear dirty bits for the entire
process only. In addition, reading info about pages is a separate
operation. It means we must freeze the process to read information
about all its pages, reset dirty bits, only then we can start dumping
pages. The information about pages becomes more and more outdated,
while we are processing pages. The new interface solves both these
downsides. First, it allows us to read pte bits and clear the
soft-dirty bit atomically. It means that CRIU will not need to freeze
processes to pre-dump their memory. Second, it clears soft-dirty bits
for a specified region of memory. It means CRIU will have actual info
about pages to the moment of dumping them.
* The new interface has to be much faster because basic page filtering
is happening in the kernel. With the old interface, we have to read
pagemap for each page.
*Implementation Evolution (Short Summary)*
From the definition of GetWriteWatch(), we feel like kernel's soft-dirty
feature can be used under the hood with some additions like:
* reset soft-dirty flag for only a specific region of memory instead of
clearing the flag for the entire process
* get and clear soft-dirty flag for a specific region atomically
So we decided to use ioctl on pagemap file to read or/and reset soft-dirty
flag. But using soft-dirty flag, sometimes we get extra pages which weren't
even written. They had become soft-dirty because of VMA merging and
VM_SOFTDIRTY flag. This breaks the definition of GetWriteWatch(). We were
able to by-pass this short coming by ignoring VM_SOFTDIRTY until David
reported that mprotect etc messes up the soft-dirty flag while ignoring
VM_SOFTDIRTY [5]. This wasn't happening until [6] got introduced. We
discussed if we can revert these patches. But we could not reach to any
conclusion. So at this point, I made couple of tries to solve this whole
VM_SOFTDIRTY issue by correcting the soft-dirty implementation:
* [7] Correct the bug fixed wrongly back in 2014. It had potential to cause
regression. We left it behind.
* [8] Keep a list of soft-dirty part of a VMA across splits and merges. I
got the reply don't increase the size of the VMA by 8 bytes.
At this point, we left soft-dirty considering it is too much delicate and
userfaultfd [9] seemed like the only way forward. From there onward, we
have been basing soft-dirty emulation on userfaultfd wp feature where
kernel resolves the faults itself when WP_ASYNC feature is used. It was
straight forward to add WP_ASYNC feature in userfautlfd. Now we get only
those pages dirty or written-to which are really written in reality. (PS
There is another WP_UNPOPULATED userfautfd feature is required which is
needed to avoid pre-faulting memory before write-protecting [9].)
All the different masks were added on the request of CRIU devs to create
interface more generic and better.
[1] https://learn.microsoft.com/en-us/windows/win32/api/memoryapi/nf-memoryapi-…
[2] https://lore.kernel.org/all/20221014134802.1361436-1-mdanylo@google.com
[3] https://github.com/google/sanitizers
[4] https://github.com/google/sanitizers/wiki/AddressSanitizerAlgorithm#64-bit
[5] https://lore.kernel.org/all/bfcae708-db21-04b4-0bbe-712badd03071@redhat.com
[6] https://lore.kernel.org/all/20220725142048.30450-1-peterx@redhat.com/
[7] https://lore.kernel.org/all/20221122115007.2787017-1-usama.anjum@collabora.…
[8] https://lore.kernel.org/all/20221220162606.1595355-1-usama.anjum@collabora.…
[9] https://lore.kernel.org/all/20230306213925.617814-1-peterx@redhat.com
[10] https://lore.kernel.org/all/20230125144529.1630917-1-mdanylo@google.com
* Original Cover letter from v8*
Hello,
Note:
Soft-dirty pages and pages which have been written-to are synonyms. As
kernel already has soft-dirty feature inside which we have given up to
use, we are using written-to terminology while using UFFD async WP under
the hood.
It is possible to find and clear soft-dirty pages entirely in userspace.
But it isn't efficient:
- The mprotect and SIGSEGV handler for bookkeeping
- The userfaultfd wp (synchronous) with the handler for bookkeeping
Some benchmarks can be seen here[1]. This series adds features that weren't
present earlier:
- There is no atomic get soft-dirty/Written-to status and clear present in
the kernel.
- The pages which have been written-to can not be found in accurate way.
(Kernel's soft-dirty PTE bit + sof_dirty VMA bit shows more soft-dirty
pages than there actually are.)
Historically, soft-dirty PTE bit tracking has been used in the CRIU
project. The procfs interface is enough for finding the soft-dirty bit
status and clearing the soft-dirty bit of all the pages of a process.
We have the use case where we need to track the soft-dirty PTE bit for
only specific pages on-demand. We need this tracking and clear mechanism
of a region of memory while the process is running to emulate the
getWriteWatch() syscall of Windows.
*(Moved to using UFFD instead of soft-dirty feature to find pages which
have been written-to from v7 patch series)*:
Stop using the soft-dirty flags for finding which pages have been
written to. It is too delicate and wrong as it shows more soft-dirty
pages than the actual soft-dirty pages. There is no interest in
correcting it [2][3] as this is how the feature was written years ago.
It shouldn't be updated to changed behaviour. Peter Xu has suggested
using the async version of the UFFD WP [4] as it is based inherently
on the PTEs.
So in this patch series, I've added a new mode to the UFFD which is
asynchronous version of the write protect. When this variant of the
UFFD WP is used, the page faults are resolved automatically by the
kernel. The pages which have been written-to can be found by reading
pagemap file (!PM_UFFD_WP). This feature can be used successfully to
find which pages have been written to from the time the pages were
write protected. This works just like the soft-dirty flag without
showing any extra pages which aren't soft-dirty in reality.
The information related to pages if the page is file mapped, present and
swapped is required for the CRIU project [5][6]. The addition of the
required mask, any mask, excluded mask and return masks are also required
for the CRIU project [5].
The IOCTL returns the addresses of the pages which match the specific
masks. The page addresses are returned in struct page_region in a compact
form. The max_pages is needed to support a use case where user only wants
to get a specific number of pages. So there is no need to find all the
pages of interest in the range when max_pages is specified. The IOCTL
returns when the maximum number of the pages are found. The max_pages is
optional. If max_pages is specified, it must be equal or greater than the
vec_size. This restriction is needed to handle worse case when one
page_region only contains info of one page and it cannot be compacted.
This is needed to emulate the Windows getWriteWatch() syscall.
The patch series include the detailed selftest which can be used as an
example for the uffd async wp test and PAGEMAP_IOCTL. It shows the
interface usages as well.
[1] https://lore.kernel.org/lkml/54d4c322-cd6e-eefd-b161-2af2b56aae24@collabora…
[2] https://lore.kernel.org/all/20221220162606.1595355-1-usama.anjum@collabora.…
[3] https://lore.kernel.org/all/20221122115007.2787017-1-usama.anjum@collabora.…
[4] https://lore.kernel.org/all/Y6Hc2d+7eTKs7AiH@x1n
[5] https://lore.kernel.org/all/YyiDg79flhWoMDZB@gmail.com/
[6] https://lore.kernel.org/all/20221014134802.1361436-1-mdanylo@google.com/
Regards,
Muhammad Usama Anjum
Muhammad Usama Anjum (5):
fs/proc/task_mmu: Implement IOCTL to get and optionally clear info
about PTEs
fs/proc/task_mmu: Add fast paths to get/clear PAGE_IS_WRITTEN flag
tools headers UAPI: Update linux/fs.h with the kernel sources
mm/pagemap: add documentation of PAGEMAP_SCAN IOCTL
selftests: mm: add pagemap ioctl tests
Peter Xu (1):
userfaultfd: UFFD_FEATURE_WP_ASYNC
Documentation/admin-guide/mm/pagemap.rst | 89 +
Documentation/admin-guide/mm/userfaultfd.rst | 35 +
fs/proc/task_mmu.c | 722 ++++++++
fs/userfaultfd.c | 26 +-
include/linux/hugetlb.h | 1 +
include/linux/userfaultfd_k.h | 28 +-
include/uapi/linux/fs.h | 59 +
include/uapi/linux/userfaultfd.h | 9 +-
mm/hugetlb.c | 34 +-
mm/memory.c | 28 +-
tools/include/uapi/linux/fs.h | 59 +
tools/testing/selftests/mm/.gitignore | 2 +
tools/testing/selftests/mm/Makefile | 3 +-
tools/testing/selftests/mm/config | 1 +
tools/testing/selftests/mm/pagemap_ioctl.c | 1660 ++++++++++++++++++
tools/testing/selftests/mm/run_vmtests.sh | 4 +
16 files changed, 2736 insertions(+), 24 deletions(-)
create mode 100644 tools/testing/selftests/mm/pagemap_ioctl.c
--
2.40.1