3822a7c409
Pull MM updates from Andrew Morton:
- Daniel Verkamp has contributed a memfd series ("mm/memfd: add
F_SEAL_EXEC") which permits the setting of the memfd execute bit at
memfd creation time, with the option of sealing the state of the X
bit.
- Peter Xu adds a patch series ("mm/hugetlb: Make huge_pte_offset()
thread-safe for pmd unshare") which addresses a rare race condition
related to PMD unsharing.
- Several folioification patch serieses from Matthew Wilcox, Vishal
Moola, Sidhartha Kumar and Lorenzo Stoakes
- Johannes Weiner has a series ("mm: push down lock_page_memcg()")
which does perform some memcg maintenance and cleanup work.
- SeongJae Park has added DAMOS filtering to DAMON, with the series
"mm/damon/core: implement damos filter".
These filters provide users with finer-grained control over DAMOS's
actions. SeongJae has also done some DAMON cleanup work.
- Kairui Song adds a series ("Clean up and fixes for swap").
- Vernon Yang contributed the series "Clean up and refinement for maple
tree".
- Yu Zhao has contributed the "mm: multi-gen LRU: memcg LRU" series. It
adds to MGLRU an LRU of memcgs, to improve the scalability of global
reclaim.
- David Hildenbrand has added some userfaultfd cleanup work in the
series "mm: uffd-wp + change_protection() cleanups".
- Christoph Hellwig has removed the generic_writepages() library
function in the series "remove generic_writepages".
- Baolin Wang has performed some maintenance on the compaction code in
his series "Some small improvements for compaction".
- Sidhartha Kumar is doing some maintenance work on struct page in his
series "Get rid of tail page fields".
- David Hildenbrand contributed some cleanup, bugfixing and
generalization of pte management and of pte debugging in his series
"mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE on all architectures with
swap PTEs".
- Mel Gorman and Neil Brown have removed the __GFP_ATOMIC allocation
flag in the series "Discard __GFP_ATOMIC".
- Sergey Senozhatsky has improved zsmalloc's memory utilization with
his series "zsmalloc: make zspage chain size configurable".
- Joey Gouly has added prctl() support for prohibiting the creation of
writeable+executable mappings.
The previous BPF-based approach had shortcomings. See "mm: In-kernel
support for memory-deny-write-execute (MDWE)".
- Waiman Long did some kmemleak cleanup and bugfixing in the series
"mm/kmemleak: Simplify kmemleak_cond_resched() & fix UAF".
- T.J. Alumbaugh has contributed some MGLRU cleanup work in his series
"mm: multi-gen LRU: improve".
- Jiaqi Yan has provided some enhancements to our memory error
statistics reporting, mainly by presenting the statistics on a
per-node basis. See the series "Introduce per NUMA node memory error
statistics".
- Mel Gorman has a second and hopefully final shot at fixing a CPU-hog
regression in compaction via his series "Fix excessive CPU usage
during compaction".
- Christoph Hellwig does some vmalloc maintenance work in the series
"cleanup vfree and vunmap".
- Christoph Hellwig has removed block_device_operations.rw_page() in
ths series "remove ->rw_page".
- We get some maple_tree improvements and cleanups in Liam Howlett's
series "VMA tree type safety and remove __vma_adjust()".
- Suren Baghdasaryan has done some work on the maintainability of our
vm_flags handling in the series "introduce vm_flags modifier
functions".
- Some pagemap cleanup and generalization work in Mike Rapoport's
series "mm, arch: add generic implementation of pfn_valid() for
FLATMEM" and "fixups for generic implementation of pfn_valid()"
- Baoquan He has done some work to make /proc/vmallocinfo and
/proc/kcore better represent the real state of things in his series
"mm/vmalloc.c: allow vread() to read out vm_map_ram areas".
- Jason Gunthorpe rationalized the GUP system's interface to the rest
of the kernel in the series "Simplify the external interface for
GUP".
- SeongJae Park wishes to migrate people from DAMON's debugfs interface
over to its sysfs interface. To support this, we'll temporarily be
printing warnings when people use the debugfs interface. See the
series "mm/damon: deprecate DAMON debugfs interface".
- Andrey Konovalov provided the accurately named "lib/stackdepot: fixes
and clean-ups" series.
- Huang Ying has provided a dramatic reduction in migration's TLB flush
IPI rates with the series "migrate_pages(): batch TLB flushing".
- Arnd Bergmann has some objtool fixups in "objtool warning fixes".
* tag 'mm-stable-2023-02-20-13-37' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (505 commits)
include/linux/migrate.h: remove unneeded externs
mm/memory_hotplug: cleanup return value handing in do_migrate_range()
mm/uffd: fix comment in handling pte markers
mm: change to return bool for isolate_movable_page()
mm: hugetlb: change to return bool for isolate_hugetlb()
mm: change to return bool for isolate_lru_page()
mm: change to return bool for folio_isolate_lru()
objtool: add UACCESS exceptions for __tsan_volatile_read/write
kmsan: disable ftrace in kmsan core code
kasan: mark addr_has_metadata __always_inline
mm: memcontrol: rename memcg_kmem_enabled()
sh: initialize max_mapnr
m68k/nommu: add missing definition of ARCH_PFN_OFFSET
mm: percpu: fix incorrect size in pcpu_obj_full_size()
maple_tree: reduce stack usage with gcc-9 and earlier
mm: page_alloc: call panic() when memoryless node allocation fails
mm: multi-gen LRU: avoid futile retries
migrate_pages: move THP/hugetlb migration support check to simplify code
migrate_pages: batch flushing TLB
migrate_pages: share more code between _unmap and _move
...
275 lines
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ReStructuredText
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ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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=======================
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DAMON-based Reclamation
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=======================
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DAMON-based Reclamation (DAMON_RECLAIM) is a static kernel module that aimed to
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be used for proactive and lightweight reclamation under light memory pressure.
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It doesn't aim to replace the LRU-list based page_granularity reclamation, but
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to be selectively used for different level of memory pressure and requirements.
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Where Proactive Reclamation is Required?
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========================================
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On general memory over-committed systems, proactively reclaiming cold pages
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helps saving memory and reducing latency spikes that incurred by the direct
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reclaim of the process or CPU consumption of kswapd, while incurring only
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minimal performance degradation [1]_ [2]_ .
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Free Pages Reporting [3]_ based memory over-commit virtualization systems are
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good example of the cases. In such systems, the guest VMs reports their free
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memory to host, and the host reallocates the reported memory to other guests.
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As a result, the memory of the systems are fully utilized. However, the
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guests could be not so memory-frugal, mainly because some kernel subsystems and
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user-space applications are designed to use as much memory as available. Then,
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guests could report only small amount of memory as free to host, results in
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memory utilization drop of the systems. Running the proactive reclamation in
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guests could mitigate this problem.
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How It Works?
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=============
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DAMON_RECLAIM finds memory regions that didn't accessed for specific time
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duration and page out. To avoid it consuming too much CPU for the paging out
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operation, a speed limit can be configured. Under the speed limit, it pages
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out memory regions that didn't accessed longer time first. System
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administrators can also configure under what situation this scheme should
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automatically activated and deactivated with three memory pressure watermarks.
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Interface: Module Parameters
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============================
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To use this feature, you should first ensure your system is running on a kernel
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that is built with ``CONFIG_DAMON_RECLAIM=y``.
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To let sysadmins enable or disable it and tune for the given system,
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DAMON_RECLAIM utilizes module parameters. That is, you can put
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``damon_reclaim.<parameter>=<value>`` on the kernel boot command line or write
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proper values to ``/sys/module/damon_reclaim/parameters/<parameter>`` files.
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Below are the description of each parameter.
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enabled
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-------
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Enable or disable DAMON_RECLAIM.
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You can enable DAMON_RCLAIM by setting the value of this parameter as ``Y``.
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Setting it as ``N`` disables DAMON_RECLAIM. Note that DAMON_RECLAIM could do
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no real monitoring and reclamation due to the watermarks-based activation
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condition. Refer to below descriptions for the watermarks parameter for this.
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commit_inputs
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-------------
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Make DAMON_RECLAIM reads the input parameters again, except ``enabled``.
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Input parameters that updated while DAMON_RECLAIM is running are not applied
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by default. Once this parameter is set as ``Y``, DAMON_RECLAIM reads values
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of parametrs except ``enabled`` again. Once the re-reading is done, this
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parameter is set as ``N``. If invalid parameters are found while the
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re-reading, DAMON_RECLAIM will be disabled.
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min_age
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-------
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Time threshold for cold memory regions identification in microseconds.
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If a memory region is not accessed for this or longer time, DAMON_RECLAIM
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identifies the region as cold, and reclaims it.
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120 seconds by default.
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quota_ms
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--------
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Limit of time for the reclamation in milliseconds.
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DAMON_RECLAIM tries to use only up to this time within a time window
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(quota_reset_interval_ms) for trying reclamation of cold pages. This can be
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used for limiting CPU consumption of DAMON_RECLAIM. If the value is zero, the
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limit is disabled.
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10 ms by default.
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quota_sz
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--------
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Limit of size of memory for the reclamation in bytes.
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DAMON_RECLAIM charges amount of memory which it tried to reclaim within a time
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window (quota_reset_interval_ms) and makes no more than this limit is tried.
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This can be used for limiting consumption of CPU and IO. If this value is
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zero, the limit is disabled.
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128 MiB by default.
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quota_reset_interval_ms
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-----------------------
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The time/size quota charge reset interval in milliseconds.
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The charget reset interval for the quota of time (quota_ms) and size
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(quota_sz). That is, DAMON_RECLAIM does not try reclamation for more than
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quota_ms milliseconds or quota_sz bytes within quota_reset_interval_ms
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milliseconds.
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1 second by default.
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wmarks_interval
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---------------
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Minimal time to wait before checking the watermarks, when DAMON_RECLAIM is
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enabled but inactive due to its watermarks rule.
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wmarks_high
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-----------
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Free memory rate (per thousand) for the high watermark.
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If free memory of the system in bytes per thousand bytes is higher than this,
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DAMON_RECLAIM becomes inactive, so it does nothing but only periodically checks
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the watermarks.
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wmarks_mid
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----------
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Free memory rate (per thousand) for the middle watermark.
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If free memory of the system in bytes per thousand bytes is between this and
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the low watermark, DAMON_RECLAIM becomes active, so starts the monitoring and
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the reclaiming.
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wmarks_low
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----------
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Free memory rate (per thousand) for the low watermark.
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If free memory of the system in bytes per thousand bytes is lower than this,
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DAMON_RECLAIM becomes inactive, so it does nothing but periodically checks the
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watermarks. In the case, the system falls back to the LRU-list based page
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granularity reclamation logic.
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sample_interval
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---------------
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Sampling interval for the monitoring in microseconds.
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The sampling interval of DAMON for the cold memory monitoring. Please refer to
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the DAMON documentation (:doc:`usage`) for more detail.
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aggr_interval
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-------------
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Aggregation interval for the monitoring in microseconds.
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The aggregation interval of DAMON for the cold memory monitoring. Please
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refer to the DAMON documentation (:doc:`usage`) for more detail.
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min_nr_regions
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--------------
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Minimum number of monitoring regions.
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The minimal number of monitoring regions of DAMON for the cold memory
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monitoring. This can be used to set lower-bound of the monitoring quality.
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But, setting this too high could result in increased monitoring overhead.
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Please refer to the DAMON documentation (:doc:`usage`) for more detail.
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max_nr_regions
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--------------
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Maximum number of monitoring regions.
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The maximum number of monitoring regions of DAMON for the cold memory
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monitoring. This can be used to set upper-bound of the monitoring overhead.
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However, setting this too low could result in bad monitoring quality. Please
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refer to the DAMON documentation (:doc:`usage`) for more detail.
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monitor_region_start
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--------------------
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Start of target memory region in physical address.
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The start physical address of memory region that DAMON_RECLAIM will do work
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against. That is, DAMON_RECLAIM will find cold memory regions in this region
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and reclaims. By default, biggest System RAM is used as the region.
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monitor_region_end
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------------------
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End of target memory region in physical address.
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The end physical address of memory region that DAMON_RECLAIM will do work
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against. That is, DAMON_RECLAIM will find cold memory regions in this region
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and reclaims. By default, biggest System RAM is used as the region.
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skip_anon
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---------
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Skip anonymous pages reclamation.
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If this parameter is set as ``Y``, DAMON_RECLAIM does not reclaim anonymous
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pages. By default, ``N``.
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kdamond_pid
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-----------
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PID of the DAMON thread.
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If DAMON_RECLAIM is enabled, this becomes the PID of the worker thread. Else,
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-1.
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nr_reclaim_tried_regions
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------------------------
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Number of memory regions that tried to be reclaimed by DAMON_RECLAIM.
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bytes_reclaim_tried_regions
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---------------------------
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Total bytes of memory regions that tried to be reclaimed by DAMON_RECLAIM.
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nr_reclaimed_regions
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--------------------
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Number of memory regions that successfully be reclaimed by DAMON_RECLAIM.
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bytes_reclaimed_regions
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-----------------------
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Total bytes of memory regions that successfully be reclaimed by DAMON_RECLAIM.
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nr_quota_exceeds
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----------------
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Number of times that the time/space quota limits have exceeded.
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Example
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=======
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Below runtime example commands make DAMON_RECLAIM to find memory regions that
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not accessed for 30 seconds or more and pages out. The reclamation is limited
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to be done only up to 1 GiB per second to avoid DAMON_RECLAIM consuming too
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much CPU time for the paging out operation. It also asks DAMON_RECLAIM to do
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nothing if the system's free memory rate is more than 50%, but start the real
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works if it becomes lower than 40%. If DAMON_RECLAIM doesn't make progress and
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therefore the free memory rate becomes lower than 20%, it asks DAMON_RECLAIM to
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do nothing again, so that we can fall back to the LRU-list based page
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granularity reclamation. ::
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# cd /sys/module/damon_reclaim/parameters
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# echo 30000000 > min_age
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# echo $((1 * 1024 * 1024 * 1024)) > quota_sz
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# echo 1000 > quota_reset_interval_ms
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# echo 500 > wmarks_high
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# echo 400 > wmarks_mid
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# echo 200 > wmarks_low
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# echo Y > enabled
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.. [1] https://research.google/pubs/pub48551/
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.. [2] https://lwn.net/Articles/787611/
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.. [3] https://www.kernel.org/doc/html/latest/mm/free_page_reporting.html
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