diff options
Diffstat (limited to 'Documentation/admin-guide/mm')
| -rw-r--r-- | Documentation/admin-guide/mm/damon/usage.rst | 124 | ||||
| -rw-r--r-- | Documentation/admin-guide/mm/ksm.rst | 11 | ||||
| -rw-r--r-- | Documentation/admin-guide/mm/memory-hotplug.rst | 12 | ||||
| -rw-r--r-- | Documentation/admin-guide/mm/pagemap.rst | 89 | ||||
| -rw-r--r-- | Documentation/admin-guide/mm/userfaultfd.rst | 35 |
5 files changed, 222 insertions, 49 deletions
diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst index 8da1b7281..da94feb97 100644 --- a/Documentation/admin-guide/mm/damon/usage.rst +++ b/Documentation/admin-guide/mm/damon/usage.rst @@ -20,18 +20,18 @@ DAMON provides below interfaces for different users. you can write and use your personalized DAMON sysfs wrapper programs that reads/writes the sysfs files instead of you. The `DAMON user space tool <https://github.com/awslabs/damo>`_ is one example of such programs. -- *debugfs interface. (DEPRECATED!)* - :ref:`This <debugfs_interface>` is almost identical to :ref:`sysfs interface - <sysfs_interface>`. This is deprecated, so users should move to the - :ref:`sysfs interface <sysfs_interface>`. If you depend on this and cannot - move, please report your usecase to damon@lists.linux.dev and - linux-mm@kvack.org. - *Kernel Space Programming Interface.* :doc:`This </mm/damon/api>` is for kernel space programmers. Using this, users can utilize every feature of DAMON most flexibly and efficiently by writing kernel space DAMON application programs for you. You can even extend DAMON for various address spaces. For detail, please refer to the interface :doc:`document </mm/damon/api>`. +- *debugfs interface. (DEPRECATED!)* + :ref:`This <debugfs_interface>` is almost identical to :ref:`sysfs interface + <sysfs_interface>`. This is deprecated, so users should move to the + :ref:`sysfs interface <sysfs_interface>`. If you depend on this and cannot + move, please report your usecase to damon@lists.linux.dev and + linux-mm@kvack.org. .. _sysfs_interface: @@ -76,7 +76,7 @@ comma (","). :: │ │ │ │ │ │ │ │ ... │ │ │ │ │ │ ... │ │ │ │ │ schemes/nr_schemes - │ │ │ │ │ │ 0/action + │ │ │ │ │ │ 0/action,apply_interval_us │ │ │ │ │ │ │ access_pattern/ │ │ │ │ │ │ │ │ sz/min,max │ │ │ │ │ │ │ │ nr_accesses/min,max @@ -105,14 +105,12 @@ having the root permission could use this directory. kdamonds/ --------- -The monitoring-related information including request specifications and results -are called DAMON context. DAMON executes each context with a kernel thread -called kdamond, and multiple kdamonds could run in parallel. - Under the ``admin`` directory, one directory, ``kdamonds``, which has files for -controlling the kdamonds exist. In the beginning, this directory has only one -file, ``nr_kdamonds``. Writing a number (``N``) to the file creates the number -of child directories named ``0`` to ``N-1``. Each directory represents each +controlling the kdamonds (refer to +:ref:`design <damon_design_execution_model_and_data_structures>` for more +details) exists. In the beginning, this directory has only one file, +``nr_kdamonds``. Writing a number (``N``) to the file creates the number of +child directories named ``0`` to ``N-1``. Each directory represents each kdamond. kdamonds/<N>/ @@ -150,9 +148,10 @@ kdamonds/<N>/contexts/ In the beginning, this directory has only one file, ``nr_contexts``. Writing a number (``N``) to the file creates the number of child directories named as -``0`` to ``N-1``. Each directory represents each monitoring context. At the -moment, only one context per kdamond is supported, so only ``0`` or ``1`` can -be written to the file. +``0`` to ``N-1``. Each directory represents each monitoring context (refer to +:ref:`design <damon_design_execution_model_and_data_structures>` for more +details). At the moment, only one context per kdamond is supported, so only +``0`` or ``1`` can be written to the file. .. _sysfs_contexts: @@ -270,8 +269,8 @@ schemes/<N>/ ------------ In each scheme directory, five directories (``access_pattern``, ``quotas``, -``watermarks``, ``filters``, ``stats``, and ``tried_regions``) and one file -(``action``) exist. +``watermarks``, ``filters``, ``stats``, and ``tried_regions``) and two files +(``action`` and ``apply_interval``) exist. The ``action`` file is for setting and getting the scheme's :ref:`action <damon_design_damos_action>`. The keywords that can be written to and read @@ -297,6 +296,9 @@ Note that support of each action depends on the running DAMON operations set - ``stat``: Do nothing but count the statistics. Supported by all operations sets. +The ``apply_interval_us`` file is for setting and getting the scheme's +:ref:`apply_interval <damon_design_damos>` in microseconds. + schemes/<N>/access_pattern/ --------------------------- @@ -392,7 +394,7 @@ pages of all memory cgroups except ``/having_care_already``.:: echo N > 1/matching Note that ``anon`` and ``memcg`` filters are currently supported only when -``paddr`` `implementation <sysfs_contexts>` is being used. +``paddr`` :ref:`implementation <sysfs_contexts>` is being used. Also, memory regions that are filtered out by ``addr`` or ``target`` filters are not counted as the scheme has tried to those, while regions that filtered @@ -430,9 +432,9 @@ that reading it returns the total size of the scheme tried regions, and creates directories named integer starting from ``0`` under this directory. Each directory contains files exposing detailed information about each of the memory region that the corresponding scheme's ``action`` has tried to be applied under -this directory, during next :ref:`aggregation interval -<sysfs_monitoring_attrs>`. The information includes address range, -``nr_accesses``, and ``age`` of the region. +this directory, during next :ref:`apply interval <damon_design_damos>` of the +corresponding scheme. The information includes address range, ``nr_accesses``, +and ``age`` of the region. Writing ``update_schemes_tried_bytes`` to the relevant ``kdamonds/<N>/state`` file will only update the ``total_bytes`` file, and will not create the @@ -495,6 +497,62 @@ Please note that it's highly recommended to use user space tools like `damo <https://github.com/awslabs/damo>`_ rather than manually reading and writing the files as above. Above is only for an example. +.. _tracepoint: + +Tracepoints for Monitoring Results +================================== + +Users can get the monitoring results via the :ref:`tried_regions +<sysfs_schemes_tried_regions>`. The interface is useful for getting a +snapshot, but it could be inefficient for fully recording all the monitoring +results. For the purpose, two trace points, namely ``damon:damon_aggregated`` +and ``damon:damos_before_apply``, are provided. ``damon:damon_aggregated`` +provides the whole monitoring results, while ``damon:damos_before_apply`` +provides the monitoring results for regions that each DAMON-based Operation +Scheme (:ref:`DAMOS <damon_design_damos>`) is gonna be applied. Hence, +``damon:damos_before_apply`` is more useful for recording internal behavior of +DAMOS, or DAMOS target access +:ref:`pattern <damon_design_damos_access_pattern>` based query-like efficient +monitoring results recording. + +While the monitoring is turned on, you could record the tracepoint events and +show results using tracepoint supporting tools like ``perf``. For example:: + + # echo on > monitor_on + # perf record -e damon:damon_aggregated & + # sleep 5 + # kill 9 $(pidof perf) + # echo off > monitor_on + # perf script + kdamond.0 46568 [027] 79357.842179: damon:damon_aggregated: target_id=0 nr_regions=11 122509119488-135708762112: 0 864 + [...] + +Each line of the perf script output represents each monitoring region. The +first five fields are as usual other tracepoint outputs. The sixth field +(``target_id=X``) shows the ide of the monitoring target of the region. The +seventh field (``nr_regions=X``) shows the total number of monitoring regions +for the target. The eighth field (``X-Y:``) shows the start (``X``) and end +(``Y``) addresses of the region in bytes. The ninth field (``X``) shows the +``nr_accesses`` of the region (refer to +:ref:`design <damon_design_region_based_sampling>` for more details of the +counter). Finally the tenth field (``X``) shows the ``age`` of the region +(refer to :ref:`design <damon_design_age_tracking>` for more details of the +counter). + +If the event was ``damon:damos_beofre_apply``, the ``perf script`` output would +be somewhat like below:: + + kdamond.0 47293 [000] 80801.060214: damon:damos_before_apply: ctx_idx=0 scheme_idx=0 target_idx=0 nr_regions=11 121932607488-135128711168: 0 136 + [...] + +Each line of the output represents each monitoring region that each DAMON-based +Operation Scheme was about to be applied at the traced time. The first five +fields are as usual. It shows the index of the DAMON context (``ctx_idx=X``) +of the scheme in the list of the contexts of the context's kdamond, the index +of the scheme (``scheme_idx=X``) in the list of the schemes of the context, in +addition to the output of ``damon_aggregated`` tracepoint. + + .. _debugfs_interface: debugfs Interface (DEPRECATED!) @@ -790,23 +848,3 @@ directory by putting the name of the context to the ``rm_contexts`` file. :: Note that ``mk_contexts``, ``rm_contexts``, and ``monitor_on`` files are in the root directory only. - - -.. _tracepoint: - -Tracepoint for Monitoring Results -================================= - -Users can get the monitoring results via the :ref:`tried_regions -<sysfs_schemes_tried_regions>` or a tracepoint, ``damon:damon_aggregated``. -While the tried regions directory is useful for getting a snapshot, the -tracepoint is useful for getting a full record of the results. While the -monitoring is turned on, you could record the tracepoint events and show -results using tracepoint supporting tools like ``perf``. For example:: - - # echo on > monitor_on - # perf record -e damon:damon_aggregated & - # sleep 5 - # kill 9 $(pidof perf) - # echo off > monitor_on - # perf script diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst index 776f244bd..e59231ac6 100644 --- a/Documentation/admin-guide/mm/ksm.rst +++ b/Documentation/admin-guide/mm/ksm.rst @@ -155,6 +155,15 @@ stable_node_chains_prune_millisecs scan. It's a noop if not a single KSM page hit the ``max_page_sharing`` yet. +smart_scan + Historically KSM checked every candidate page for each scan. It did + not take into account historic information. When smart scan is + enabled, pages that have previously not been de-duplicated get + skipped. How often these pages are skipped depends on how often + de-duplication has already been tried and failed. By default this + optimization is enabled. The ``pages_skipped`` metric shows how + effective the setting is. + The effectiveness of KSM and MADV_MERGEABLE is shown in ``/sys/kernel/mm/ksm/``: general_profit @@ -169,6 +178,8 @@ pages_unshared how many pages unique but repeatedly checked for merging pages_volatile how many pages changing too fast to be placed in a tree +pages_skipped + how many pages did the "smart" page scanning algorithm skip full_scans how many times all mergeable areas have been scanned stable_node_chains diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst index cfe034cf1..098f14d83 100644 --- a/Documentation/admin-guide/mm/memory-hotplug.rst +++ b/Documentation/admin-guide/mm/memory-hotplug.rst @@ -33,7 +33,7 @@ used to expose persistent memory, other performance-differentiated memory and reserved memory regions as ordinary system RAM to Linux. Linux only supports memory hot(un)plug on selected 64 bit architectures, such as -x86_64, arm64, ppc64, s390x and ia64. +x86_64, arm64, ppc64 and s390x. Memory Hot(Un)Plug Granularity ------------------------------ @@ -75,7 +75,7 @@ Memory hotunplug consists of two phases: (1) Offlining memory blocks (2) Removing the memory from Linux -In the fist phase, memory is "hidden" from the page allocator again, for +In the first phase, memory is "hidden" from the page allocator again, for example, by migrating busy memory to other memory locations and removing all relevant free pages from the page allocator After this phase, the memory is no longer visible in memory statistics of the system. @@ -250,15 +250,15 @@ Observing the State of Memory Blocks The state (online/offline/going-offline) of a memory block can be observed either via:: - % cat /sys/device/system/memory/memoryXXX/state + % cat /sys/devices/system/memory/memoryXXX/state Or alternatively (1/0) via:: - % cat /sys/device/system/memory/memoryXXX/online + % cat /sys/devices/system/memory/memoryXXX/online For an online memory block, the managing zone can be observed via:: - % cat /sys/device/system/memory/memoryXXX/valid_zones + % cat /sys/devices/system/memory/memoryXXX/valid_zones Configuring Memory Hot(Un)Plug ============================== @@ -326,7 +326,7 @@ however, a memory block might span memory holes. A memory block spanning memory holes cannot be offlined. For example, assume 1 GiB memory block size. A device for a memory starting at -0x100000000 is ``/sys/device/system/memory/memory4``:: +0x100000000 is ``/sys/devices/system/memory/memory4``:: (0x100000000 / 1Gib = 4) diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst index c8f380271..fe17cf210 100644 --- a/Documentation/admin-guide/mm/pagemap.rst +++ b/Documentation/admin-guide/mm/pagemap.rst @@ -227,3 +227,92 @@ Before Linux 3.11 pagemap bits 55-60 were used for "page-shift" (which is always 12 at most architectures). Since Linux 3.11 their meaning changes after first clear of soft-dirty bits. Since Linux 4.2 they are used for flags unconditionally. + +Pagemap Scan IOCTL +================== + +The ``PAGEMAP_SCAN`` IOCTL on the pagemap file can be used to get or optionally +clear the info about page table entries. The following operations are supported +in this IOCTL: + +- Scan the address range and get the memory ranges matching the provided criteria. + This is performed when the output buffer is specified. +- Write-protect the pages. The ``PM_SCAN_WP_MATCHING`` is used to write-protect + the pages of interest. The ``PM_SCAN_CHECK_WPASYNC`` aborts the operation if + non-Async Write Protected pages are found. The ``PM_SCAN_WP_MATCHING`` can be + used with or without ``PM_SCAN_CHECK_WPASYNC``. +- Both of those operations can be combined into one atomic operation where we can + get and write protect the pages as well. + +Following flags about pages are currently supported: + +- ``PAGE_IS_WPALLOWED`` - Page has async-write-protection enabled +- ``PAGE_IS_WRITTEN`` - Page has been written to from the time it was write protected +- ``PAGE_IS_FILE`` - Page is file backed +- ``PAGE_IS_PRESENT`` - Page is present in the memory +- ``PAGE_IS_SWAPPED`` - Page is in swapped +- ``PAGE_IS_PFNZERO`` - Page has zero PFN +- ``PAGE_IS_HUGE`` - Page is THP or Hugetlb backed + +The ``struct pm_scan_arg`` is used as the argument of the IOCTL. + + 1. The size of the ``struct pm_scan_arg`` must be specified in the ``size`` + field. This field will be helpful in recognizing the structure if extensions + are done later. + 2. The flags can be specified in the ``flags`` field. The ``PM_SCAN_WP_MATCHING`` + and ``PM_SCAN_CHECK_WPASYNC`` are the only added flags at this time. The get + operation is optionally performed depending upon if the output buffer is + provided or not. + 3. The range is specified through ``start`` and ``end``. + 4. The walk can abort before visiting the complete range such as the user buffer + can get full etc. The walk ending address is specified in``end_walk``. + 5. The output buffer of ``struct page_region`` array and size is specified in + ``vec`` and ``vec_len``. + 6. The optional maximum requested pages are specified in the ``max_pages``. + 7. The masks are specified in ``category_mask``, ``category_anyof_mask``, + ``category_inverted`` and ``return_mask``. + +Find pages which have been written and WP them as well:: + + struct pm_scan_arg arg = { + .size = sizeof(arg), + .flags = PM_SCAN_CHECK_WPASYNC | PM_SCAN_CHECK_WPASYNC, + .. + .category_mask = PAGE_IS_WRITTEN, + .return_mask = PAGE_IS_WRITTEN, + }; + +Find pages which have been written, are file backed, not swapped and either +present or huge:: + + struct pm_scan_arg arg = { + .size = sizeof(arg), + .flags = 0, + .. + .category_mask = PAGE_IS_WRITTEN | PAGE_IS_SWAPPED, + .category_inverted = PAGE_IS_SWAPPED, + .category_anyof_mask = PAGE_IS_PRESENT | PAGE_IS_HUGE, + .return_mask = PAGE_IS_WRITTEN | PAGE_IS_SWAPPED | + PAGE_IS_PRESENT | PAGE_IS_HUGE, + }; + +The ``PAGE_IS_WRITTEN`` flag can be considered as a better-performing alternative +of soft-dirty flag. It doesn't get affected by VMA merging of the kernel and hence +the user can find the true soft-dirty pages in case of normal pages. (There may +still be extra dirty pages reported for THP or Hugetlb pages.) + +"PAGE_IS_WRITTEN" category is used with uffd write protect-enabled ranges to +implement memory dirty tracking in userspace: + + 1. The userfaultfd file descriptor is created with ``userfaultfd`` syscall. + 2. The ``UFFD_FEATURE_WP_UNPOPULATED`` and ``UFFD_FEATURE_WP_ASYNC`` features + are set by ``UFFDIO_API`` IOCTL. + 3. The memory range is registered with ``UFFDIO_REGISTER_MODE_WP`` mode + through ``UFFDIO_REGISTER`` IOCTL. + 4. Then any part of the registered memory or the whole memory region must + be write protected using ``PAGEMAP_SCAN`` IOCTL with flag ``PM_SCAN_WP_MATCHING`` + or the ``UFFDIO_WRITEPROTECT`` IOCTL can be used. Both of these perform the + same operation. The former is better in terms of performance. + 5. Now the ``PAGEMAP_SCAN`` IOCTL can be used to either just find pages which + have been written to since they were last marked and/or optionally write protect + the pages as well. diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst index 4349a8c2b..203e26da5 100644 --- a/Documentation/admin-guide/mm/userfaultfd.rst +++ b/Documentation/admin-guide/mm/userfaultfd.rst @@ -244,6 +244,41 @@ write-protected (so future writes will also result in a WP fault). These ioctls support a mode flag (``UFFDIO_COPY_MODE_WP`` or ``UFFDIO_CONTINUE_MODE_WP`` respectively) to configure the mapping this way. +If the userfaultfd context has ``UFFD_FEATURE_WP_ASYNC`` feature bit set, +any vma registered with write-protection will work in async mode rather +than the default sync mode. + +In async mode, there will be no message generated when a write operation +happens, meanwhile the write-protection will be resolved automatically by +the kernel. It can be seen as a more accurate version of soft-dirty +tracking and it can be different in a few ways: + + - The dirty result will not be affected by vma changes (e.g. vma + merging) because the dirty is only tracked by the pte. + + - It supports range operations by default, so one can enable tracking on + any range of memory as long as page aligned. + + - Dirty information will not get lost if the pte was zapped due to + various reasons (e.g. during split of a shmem transparent huge page). + + - Due to a reverted meaning of soft-dirty (page clean when uffd-wp bit + set; dirty when uffd-wp bit cleared), it has different semantics on + some of the memory operations. For example: ``MADV_DONTNEED`` on + anonymous (or ``MADV_REMOVE`` on a file mapping) will be treated as + dirtying of memory by dropping uffd-wp bit during the procedure. + +The user app can collect the "written/dirty" status by looking up the +uffd-wp bit for the pages being interested in /proc/pagemap. + +The page will not be under track of uffd-wp async mode until the page is +explicitly write-protected by ``ioctl(UFFDIO_WRITEPROTECT)`` with the mode +flag ``UFFDIO_WRITEPROTECT_MODE_WP`` set. Trying to resolve a page fault +that was tracked by async mode userfaultfd-wp is invalid. + +When userfaultfd-wp async mode is used alone, it can be applied to all +kinds of memory. + Memory Poisioning Emulation --------------------------- |