diff options
Diffstat (limited to 'Documentation/admin-guide/mm')
| -rw-r--r-- | Documentation/admin-guide/mm/damon/usage.rst | 147 | ||||
| -rw-r--r-- | Documentation/admin-guide/mm/ksm.rst | 55 | ||||
| -rw-r--r-- | Documentation/admin-guide/mm/pagemap.rst | 1 | ||||
| -rw-r--r-- | Documentation/admin-guide/mm/transhuge.rst | 97 | ||||
| -rw-r--r-- | Documentation/admin-guide/mm/userfaultfd.rst | 3 | ||||
| -rw-r--r-- | Documentation/admin-guide/mm/zswap.rst | 20 |
6 files changed, 261 insertions, 62 deletions
diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst index da94feb97ed1..9d23144bf985 100644 --- a/Documentation/admin-guide/mm/damon/usage.rst +++ b/Documentation/admin-guide/mm/damon/usage.rst @@ -59,41 +59,47 @@ Files Hierarchy The files hierarchy of DAMON sysfs interface is shown below. In the below figure, parents-children relations are represented with indentations, each directory is having ``/`` suffix, and files in each directory are separated by -comma (","). :: - - /sys/kernel/mm/damon/admin - │ kdamonds/nr_kdamonds - │ │ 0/state,pid - │ │ │ contexts/nr_contexts - │ │ │ │ 0/avail_operations,operations - │ │ │ │ │ monitoring_attrs/ +comma (","). + +.. parsed-literal:: + + :ref:`/sys/kernel/mm/damon <sysfs_root>`/admin + │ :ref:`kdamonds <sysfs_kdamonds>`/nr_kdamonds + │ │ :ref:`0 <sysfs_kdamond>`/state,pid + │ │ │ :ref:`contexts <sysfs_contexts>`/nr_contexts + │ │ │ │ :ref:`0 <sysfs_context>`/avail_operations,operations + │ │ │ │ │ :ref:`monitoring_attrs <sysfs_monitoring_attrs>`/ │ │ │ │ │ │ intervals/sample_us,aggr_us,update_us │ │ │ │ │ │ nr_regions/min,max - │ │ │ │ │ targets/nr_targets - │ │ │ │ │ │ 0/pid_target - │ │ │ │ │ │ │ regions/nr_regions - │ │ │ │ │ │ │ │ 0/start,end + │ │ │ │ │ :ref:`targets <sysfs_targets>`/nr_targets + │ │ │ │ │ │ :ref:`0 <sysfs_target>`/pid_target + │ │ │ │ │ │ │ :ref:`regions <sysfs_regions>`/nr_regions + │ │ │ │ │ │ │ │ :ref:`0 <sysfs_region>`/start,end │ │ │ │ │ │ │ │ ... │ │ │ │ │ │ ... - │ │ │ │ │ schemes/nr_schemes - │ │ │ │ │ │ 0/action,apply_interval_us - │ │ │ │ │ │ │ access_pattern/ + │ │ │ │ │ :ref:`schemes <sysfs_schemes>`/nr_schemes + │ │ │ │ │ │ :ref:`0 <sysfs_scheme>`/action,apply_interval_us + │ │ │ │ │ │ │ :ref:`access_pattern <sysfs_access_pattern>`/ │ │ │ │ │ │ │ │ sz/min,max │ │ │ │ │ │ │ │ nr_accesses/min,max │ │ │ │ │ │ │ │ age/min,max - │ │ │ │ │ │ │ quotas/ms,bytes,reset_interval_ms + │ │ │ │ │ │ │ :ref:`quotas <sysfs_quotas>`/ms,bytes,reset_interval_ms │ │ │ │ │ │ │ │ weights/sz_permil,nr_accesses_permil,age_permil - │ │ │ │ │ │ │ watermarks/metric,interval_us,high,mid,low - │ │ │ │ │ │ │ filters/nr_filters + │ │ │ │ │ │ │ │ :ref:`goals <sysfs_schemes_quota_goals>`/nr_goals + │ │ │ │ │ │ │ │ │ 0/target_value,current_value + │ │ │ │ │ │ │ :ref:`watermarks <sysfs_watermarks>`/metric,interval_us,high,mid,low + │ │ │ │ │ │ │ :ref:`filters <sysfs_filters>`/nr_filters │ │ │ │ │ │ │ │ 0/type,matching,memcg_id - │ │ │ │ │ │ │ stats/nr_tried,sz_tried,nr_applied,sz_applied,qt_exceeds - │ │ │ │ │ │ │ tried_regions/total_bytes + │ │ │ │ │ │ │ :ref:`stats <sysfs_schemes_stats>`/nr_tried,sz_tried,nr_applied,sz_applied,qt_exceeds + │ │ │ │ │ │ │ :ref:`tried_regions <sysfs_schemes_tried_regions>`/total_bytes │ │ │ │ │ │ │ │ 0/start,end,nr_accesses,age │ │ │ │ │ │ │ │ ... │ │ │ │ │ │ ... │ │ │ │ ... │ │ ... +.. _sysfs_root: + Root ---- @@ -102,6 +108,8 @@ has one directory named ``admin``. The directory contains the files for privileged user space programs' control of DAMON. User space tools or daemons having the root permission could use this directory. +.. _sysfs_kdamonds: + kdamonds/ --------- @@ -113,6 +121,8 @@ details) exists. In the beginning, this directory has only one file, child directories named ``0`` to ``N-1``. Each directory represents each kdamond. +.. _sysfs_kdamond: + kdamonds/<N>/ ------------- @@ -120,29 +130,37 @@ In each kdamond directory, two files (``state`` and ``pid``) and one directory (``contexts``) exist. Reading ``state`` returns ``on`` if the kdamond is currently running, or -``off`` if it is not running. Writing ``on`` or ``off`` makes the kdamond be -in the state. Writing ``commit`` to the ``state`` file makes kdamond reads the -user inputs in the sysfs files except ``state`` file again. Writing -``update_schemes_stats`` to ``state`` file updates the contents of stats files -for each DAMON-based operation scheme of the kdamond. For details of the -stats, please refer to :ref:`stats section <sysfs_schemes_stats>`. - -Writing ``update_schemes_tried_regions`` to ``state`` file updates the -DAMON-based operation scheme action tried regions directory for each -DAMON-based operation scheme of the kdamond. Writing -``update_schemes_tried_bytes`` to ``state`` file updates only -``.../tried_regions/total_bytes`` files. Writing -``clear_schemes_tried_regions`` to ``state`` file clears the DAMON-based -operating scheme action tried regions directory for each DAMON-based operation -scheme of the kdamond. For details of the DAMON-based operation scheme action -tried regions directory, please refer to :ref:`tried_regions section -<sysfs_schemes_tried_regions>`. +``off`` if it is not running. + +Users can write below commands for the kdamond to the ``state`` file. + +- ``on``: Start running. +- ``off``: Stop running. +- ``commit``: Read the user inputs in the sysfs files except ``state`` file + again. +- ``commit_schemes_quota_goals``: Read the DAMON-based operation schemes' + :ref:`quota goals <sysfs_schemes_quota_goals>`. +- ``update_schemes_stats``: Update the contents of stats files for each + DAMON-based operation scheme of the kdamond. For details of the stats, + please refer to :ref:`stats section <sysfs_schemes_stats>`. +- ``update_schemes_tried_regions``: Update the DAMON-based operation scheme + action tried regions directory for each DAMON-based operation scheme of the + kdamond. For details of the DAMON-based operation scheme action tried + regions directory, please refer to + :ref:`tried_regions section <sysfs_schemes_tried_regions>`. +- ``update_schemes_tried_bytes``: Update only ``.../tried_regions/total_bytes`` + files. +- ``clear_schemes_tried_regions``: Clear the DAMON-based operating scheme + action tried regions directory for each DAMON-based operation scheme of the + kdamond. If the state is ``on``, reading ``pid`` shows the pid of the kdamond thread. ``contexts`` directory contains files for controlling the monitoring contexts that this kdamond will execute. +.. _sysfs_contexts: + kdamonds/<N>/contexts/ ---------------------- @@ -153,7 +171,7 @@ number (``N``) to the file creates the number of child directories named as details). At the moment, only one context per kdamond is supported, so only ``0`` or ``1`` can be written to the file. -.. _sysfs_contexts: +.. _sysfs_context: contexts/<N>/ ------------- @@ -203,6 +221,8 @@ writing to and rading from the files. For more details about the intervals and monitoring regions range, please refer to the Design document (:doc:`/mm/damon/design`). +.. _sysfs_targets: + contexts/<N>/targets/ --------------------- @@ -210,6 +230,8 @@ In the beginning, this directory has only one file, ``nr_targets``. Writing a number (``N``) to the file creates the number of child directories named ``0`` to ``N-1``. Each directory represents each monitoring target. +.. _sysfs_target: + targets/<N>/ ------------ @@ -244,6 +266,8 @@ In the beginning, this directory has only one file, ``nr_regions``. Writing a number (``N``) to the file creates the number of child directories named ``0`` to ``N-1``. Each directory represents each initial monitoring target region. +.. _sysfs_region: + regions/<N>/ ------------ @@ -254,6 +278,8 @@ region by writing to and reading from the files, respectively. Each region should not overlap with others. ``end`` of directory ``N`` should be equal or smaller than ``start`` of directory ``N+1``. +.. _sysfs_schemes: + contexts/<N>/schemes/ --------------------- @@ -265,6 +291,8 @@ In the beginning, this directory has only one file, ``nr_schemes``. Writing a number (``N``) to the file creates the number of child directories named ``0`` to ``N-1``. Each directory represents each DAMON-based operation scheme. +.. _sysfs_scheme: + schemes/<N>/ ------------ @@ -277,7 +305,7 @@ The ``action`` file is for setting and getting the scheme's :ref:`action from the file and their meaning are as below. Note that support of each action depends on the running DAMON operations set -:ref:`implementation <sysfs_contexts>`. +:ref:`implementation <sysfs_context>`. - ``willneed``: Call ``madvise()`` for the region with ``MADV_WILLNEED``. Supported by ``vaddr`` and ``fvaddr`` operations set. @@ -299,6 +327,8 @@ Note that support of each action depends on the running DAMON operations set The ``apply_interval_us`` file is for setting and getting the scheme's :ref:`apply_interval <damon_design_damos>` in microseconds. +.. _sysfs_access_pattern: + schemes/<N>/access_pattern/ --------------------------- @@ -312,6 +342,8 @@ to and reading from the ``min`` and ``max`` files under ``sz``, ``nr_accesses``, and ``age`` directories, respectively. Note that the ``min`` and the ``max`` form a closed interval. +.. _sysfs_quotas: + schemes/<N>/quotas/ ------------------- @@ -319,8 +351,7 @@ The directory for the :ref:`quotas <damon_design_damos_quotas>` of the given DAMON-based operation scheme. Under ``quotas`` directory, three files (``ms``, ``bytes``, -``reset_interval_ms``) and one directory (``weights``) having three files -(``sz_permil``, ``nr_accesses_permil``, and ``age_permil``) in it exist. +``reset_interval_ms``) and two directores (``weights`` and ``goals``) exist. You can set the ``time quota`` in milliseconds, ``size quota`` in bytes, and ``reset interval`` in milliseconds by writing the values to the three files, @@ -330,11 +361,37 @@ apply the action to only up to ``bytes`` bytes of memory regions within the ``reset_interval_ms``. Setting both ``ms`` and ``bytes`` zero disables the quota limits. -You can also set the :ref:`prioritization weights +Under ``weights`` directory, three files (``sz_permil``, +``nr_accesses_permil``, and ``age_permil``) exist. +You can set the :ref:`prioritization weights <damon_design_damos_quotas_prioritization>` for size, access frequency, and age in per-thousand unit by writing the values to the three files under the ``weights`` directory. +.. _sysfs_schemes_quota_goals: + +schemes/<N>/quotas/goals/ +------------------------- + +The directory for the :ref:`automatic quota tuning goals +<damon_design_damos_quotas_auto_tuning>` of the given DAMON-based operation +scheme. + +In the beginning, this directory has only one file, ``nr_goals``. Writing a +number (``N``) to the file creates the number of child directories named ``0`` +to ``N-1``. Each directory represents each goal and current achievement. +Among the multiple feedback, the best one is used. + +Each goal directory contains two files, namely ``target_value`` and +``current_value``. Users can set and get any number to those files to set the +feedback. User space main workload's latency or throughput, system metrics +like free memory ratio or memory pressure stall time (PSI) could be example +metrics for the values. Note that users should write +``commit_schemes_quota_goals`` to the ``state`` file of the :ref:`kdamond +directory <sysfs_kdamond>` to pass the feedback to DAMON. + +.. _sysfs_watermarks: + schemes/<N>/watermarks/ ----------------------- @@ -354,6 +411,8 @@ as below. The ``interval`` should written in microseconds unit. +.. _sysfs_filters: + schemes/<N>/filters/ -------------------- @@ -394,7 +453,7 @@ 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`` :ref:`implementation <sysfs_contexts>` is being used. +``paddr`` :ref:`implementation <sysfs_context>` 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 @@ -449,6 +508,8 @@ and query-like efficient data access monitoring results retrievals. For the latter use case, in particular, users can set the ``action`` as ``stat`` and set the ``access pattern`` as their interested pattern that they want to query. +.. _sysfs_schemes_tried_region: + tried_regions/<N>/ ------------------ diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst index e59231ac6bb7..a639cac12477 100644 --- a/Documentation/admin-guide/mm/ksm.rst +++ b/Documentation/admin-guide/mm/ksm.rst @@ -80,6 +80,9 @@ pages_to_scan how many pages to scan before ksmd goes to sleep e.g. ``echo 100 > /sys/kernel/mm/ksm/pages_to_scan``. + The pages_to_scan value cannot be changed if ``advisor_mode`` has + been set to scan-time. + Default: 100 (chosen for demonstration purposes) sleep_millisecs @@ -164,6 +167,29 @@ smart_scan optimization is enabled. The ``pages_skipped`` metric shows how effective the setting is. +advisor_mode + The ``advisor_mode`` selects the current advisor. Two modes are + supported: none and scan-time. The default is none. By setting + ``advisor_mode`` to scan-time, the scan time advisor is enabled. + The section about ``advisor`` explains in detail how the scan time + advisor works. + +adivsor_max_cpu + specifies the upper limit of the cpu percent usage of the ksmd + background thread. The default is 70. + +advisor_target_scan_time + specifies the target scan time in seconds to scan all the candidate + pages. The default value is 200 seconds. + +advisor_min_pages_to_scan + specifies the lower limit of the ``pages_to_scan`` parameter of the + scan time advisor. The default is 500. + +adivsor_max_pages_to_scan + specifies the upper limit of the ``pages_to_scan`` parameter of the + scan time advisor. The default is 30000. + The effectiveness of KSM and MADV_MERGEABLE is shown in ``/sys/kernel/mm/ksm/``: general_profit @@ -263,6 +289,35 @@ ksm_swpin_copy note that KSM page might be copied when swapping in because do_swap_page() cannot do all the locking needed to reconstitute a cross-anon_vma KSM page. +Advisor +======= + +The number of candidate pages for KSM is dynamic. It can be often observed +that during the startup of an application more candidate pages need to be +processed. Without an advisor the ``pages_to_scan`` parameter needs to be +sized for the maximum number of candidate pages. The scan time advisor can +changes the ``pages_to_scan`` parameter based on demand. + +The advisor can be enabled, so KSM can automatically adapt to changes in the +number of candidate pages to scan. Two advisors are implemented: none and +scan-time. With none, no advisor is enabled. The default is none. + +The scan time advisor changes the ``pages_to_scan`` parameter based on the +observed scan times. The possible values for the ``pages_to_scan`` parameter is +limited by the ``advisor_max_cpu`` parameter. In addition there is also the +``advisor_target_scan_time`` parameter. This parameter sets the target time to +scan all the KSM candidate pages. The parameter ``advisor_target_scan_time`` +decides how aggressive the scan time advisor scans candidate pages. Lower +values make the scan time advisor to scan more aggresively. This is the most +important parameter for the configuration of the scan time advisor. + +The initial value and the maximum value can be changed with +``advisor_min_pages_to_scan`` and ``advisor_max_pages_to_scan``. The default +values are sufficient for most workloads and use cases. + +The ``pages_to_scan`` parameter is re-calculated after a scan has been completed. + + -- Izik Eidus, Hugh Dickins, 17 Nov 2009 diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst index fe17cf210426..f5f065c67615 100644 --- a/Documentation/admin-guide/mm/pagemap.rst +++ b/Documentation/admin-guide/mm/pagemap.rst @@ -253,6 +253,7 @@ Following flags about pages are currently supported: - ``PAGE_IS_SWAPPED`` - Page is in swapped - ``PAGE_IS_PFNZERO`` - Page has zero PFN - ``PAGE_IS_HUGE`` - Page is THP or Hugetlb backed +- ``PAGE_IS_SOFT_DIRTY`` - Page is soft-dirty The ``struct pm_scan_arg`` is used as the argument of the IOCTL. diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst index b0cc8243e093..04eb45a2f940 100644 --- a/Documentation/admin-guide/mm/transhuge.rst +++ b/Documentation/admin-guide/mm/transhuge.rst @@ -45,10 +45,25 @@ components: the two is using hugepages just because of the fact the TLB miss is going to run faster. +Modern kernels support "multi-size THP" (mTHP), which introduces the +ability to allocate memory in blocks that are bigger than a base page +but smaller than traditional PMD-size (as described above), in +increments of a power-of-2 number of pages. mTHP can back anonymous +memory (for example 16K, 32K, 64K, etc). These THPs continue to be +PTE-mapped, but in many cases can still provide similar benefits to +those outlined above: Page faults are significantly reduced (by a +factor of e.g. 4, 8, 16, etc), but latency spikes are much less +prominent because the size of each page isn't as huge as the PMD-sized +variant and there is less memory to clear in each page fault. Some +architectures also employ TLB compression mechanisms to squeeze more +entries in when a set of PTEs are virtually and physically contiguous +and approporiately aligned. In this case, TLB misses will occur less +often. + THP can be enabled system wide or restricted to certain tasks or even memory ranges inside task's address space. Unless THP is completely disabled, there is ``khugepaged`` daemon that scans memory and -collapses sequences of basic pages into huge pages. +collapses sequences of basic pages into PMD-sized huge pages. The THP behaviour is controlled via :ref:`sysfs <thp_sysfs>` interface and using madvise(2) and prctl(2) system calls. @@ -95,12 +110,40 @@ Global THP controls Transparent Hugepage Support for anonymous memory can be entirely disabled (mostly for debugging purposes) or only enabled inside MADV_HUGEPAGE regions (to avoid the risk of consuming more memory resources) or enabled -system wide. This can be achieved with one of:: +system wide. This can be achieved per-supported-THP-size with one of:: + + echo always >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled + echo madvise >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled + echo never >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled + +where <size> is the hugepage size being addressed, the available sizes +for which vary by system. + +For example:: + + echo always >/sys/kernel/mm/transparent_hugepage/hugepages-2048kB/enabled + +Alternatively it is possible to specify that a given hugepage size +will inherit the top-level "enabled" value:: + + echo inherit >/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/enabled + +For example:: + + echo inherit >/sys/kernel/mm/transparent_hugepage/hugepages-2048kB/enabled + +The top-level setting (for use with "inherit") can be set by issuing +one of the following commands:: echo always >/sys/kernel/mm/transparent_hugepage/enabled echo madvise >/sys/kernel/mm/transparent_hugepage/enabled echo never >/sys/kernel/mm/transparent_hugepage/enabled +By default, PMD-sized hugepages have enabled="inherit" and all other +hugepage sizes have enabled="never". If enabling multiple hugepage +sizes, the kernel will select the most appropriate enabled size for a +given allocation. + It's also possible to limit defrag efforts in the VM to generate anonymous hugepages in case they're not immediately free to madvise regions or to never try to defrag memory and simply fallback to regular @@ -146,25 +189,34 @@ madvise never should be self-explanatory. -By default kernel tries to use huge zero page on read page fault to -anonymous mapping. It's possible to disable huge zero page by writing 0 -or enable it back by writing 1:: +By default kernel tries to use huge, PMD-mappable zero page on read +page fault to anonymous mapping. It's possible to disable huge zero +page by writing 0 or enable it back by writing 1:: echo 0 >/sys/kernel/mm/transparent_hugepage/use_zero_page echo 1 >/sys/kernel/mm/transparent_hugepage/use_zero_page -Some userspace (such as a test program, or an optimized memory allocation -library) may want to know the size (in bytes) of a transparent hugepage:: +Some userspace (such as a test program, or an optimized memory +allocation library) may want to know the size (in bytes) of a +PMD-mappable transparent hugepage:: cat /sys/kernel/mm/transparent_hugepage/hpage_pmd_size -khugepaged will be automatically started when -transparent_hugepage/enabled is set to "always" or "madvise, and it'll -be automatically shutdown if it's set to "never". +khugepaged will be automatically started when one or more hugepage +sizes are enabled (either by directly setting "always" or "madvise", +or by setting "inherit" while the top-level enabled is set to "always" +or "madvise"), and it'll be automatically shutdown when the last +hugepage size is disabled (either by directly setting "never", or by +setting "inherit" while the top-level enabled is set to "never"). Khugepaged controls ------------------- +.. note:: + khugepaged currently only searches for opportunities to collapse to + PMD-sized THP and no attempt is made to collapse to other THP + sizes. + khugepaged runs usually at low frequency so while one may not want to invoke defrag algorithms synchronously during the page faults, it should be worth invoking defrag at least in khugepaged. However it's @@ -282,19 +334,26 @@ force Need of application restart =========================== -The transparent_hugepage/enabled values and tmpfs mount option only affect -future behavior. So to make them effective you need to restart any -application that could have been using hugepages. This also applies to the -regions registered in khugepaged. +The transparent_hugepage/enabled and +transparent_hugepage/hugepages-<size>kB/enabled values and tmpfs mount +option only affect future behavior. So to make them effective you need +to restart any application that could have been using hugepages. This +also applies to the regions registered in khugepaged. Monitoring usage ================ -The number of anonymous transparent huge pages currently used by the +.. note:: + Currently the below counters only record events relating to + PMD-sized THP. Events relating to other THP sizes are not included. + +The number of PMD-sized anonymous transparent huge pages currently used by the system is available by reading the AnonHugePages field in ``/proc/meminfo``. -To identify what applications are using anonymous transparent huge pages, -it is necessary to read ``/proc/PID/smaps`` and count the AnonHugePages fields -for each mapping. +To identify what applications are using PMD-sized anonymous transparent huge +pages, it is necessary to read ``/proc/PID/smaps`` and count the AnonHugePages +fields for each mapping. (Note that AnonHugePages only applies to traditional +PMD-sized THP for historical reasons and should have been called +AnonHugePmdMapped). The number of file transparent huge pages mapped to userspace is available by reading ShmemPmdMapped and ShmemHugePages fields in ``/proc/meminfo``. @@ -413,7 +472,7 @@ for huge pages. Optimizing the applications =========================== -To be guaranteed that the kernel will map a 2M page immediately in any +To be guaranteed that the kernel will map a THP immediately in any memory region, the mmap region has to be hugepage naturally aligned. posix_memalign() can provide that guarantee. diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst index 203e26da5f92..e5cc8848dcb3 100644 --- a/Documentation/admin-guide/mm/userfaultfd.rst +++ b/Documentation/admin-guide/mm/userfaultfd.rst @@ -113,6 +113,9 @@ events, except page fault notifications, may be generated: areas. ``UFFD_FEATURE_MINOR_SHMEM`` is the analogous feature indicating support for shmem virtual memory areas. +- ``UFFD_FEATURE_MOVE`` indicates that the kernel supports moving an + existing page contents from userspace. + The userland application should set the feature flags it intends to use when invoking the ``UFFDIO_API`` ioctl, to request that those features be enabled if supported. diff --git a/Documentation/admin-guide/mm/zswap.rst b/Documentation/admin-guide/mm/zswap.rst index 45b98390e938..b42132969e31 100644 --- a/Documentation/admin-guide/mm/zswap.rst +++ b/Documentation/admin-guide/mm/zswap.rst @@ -153,6 +153,26 @@ attribute, e. g.:: Setting this parameter to 100 will disable the hysteresis. +Some users cannot tolerate the swapping that comes with zswap store failures +and zswap writebacks. Swapping can be disabled entirely (without disabling +zswap itself) on a cgroup-basis as follows: + + echo 0 > /sys/fs/cgroup/<cgroup-name>/memory.zswap.writeback + +Note that if the store failures are recurring (for e.g if the pages are +incompressible), users can observe reclaim inefficiency after disabling +writeback (because the same pages might be rejected again and again). + +When there is a sizable amount of cold memory residing in the zswap pool, it +can be advantageous to proactively write these cold pages to swap and reclaim +the memory for other use cases. By default, the zswap shrinker is disabled. +User can enable it as follows: + + echo Y > /sys/module/zswap/parameters/shrinker_enabled + +This can be enabled at the boot time if ``CONFIG_ZSWAP_SHRINKER_DEFAULT_ON`` is +selected. + A debugfs interface is provided for various statistic about pool size, number of pages stored, same-value filled pages and various counters for the reasons pages are rejected. |