mm/damon/reclaim.rst

1 .. SPDX-License-Identifier: GPL-2.0
4 DAMON-based Reclamation
7 DAMON-based Reclamation (DAMON_RECLAIM) is a static kernel module that aimed to
9 It doesn't aim to replace the LRU-list based page_granularity reclamation, but
15 On general memory over-committed systems, proactively reclaiming cold pages
20 Free Pages Reporting [3]_ based memory over-commit virtualization systems are
21 good example of the cases.  In such systems, the guest VMs reports their free
24 guests could be not so memory-frugal, mainly because some kernel subsystems and
25 user-space applications are designed to use as much memory as available.  Then,
26 guests could report only small amount of memory as free to host, results in
27 memory utilization drop of the systems.  Running the proactive reclamation in
43 To use this feature, you should first ensure your system is running on a kernel
54 -------
60 no real monitoring and reclamation due to the watermarks-based activation
64 -------------
68 Input parameters that updated while DAMON_RECLAIM is running are not applied
70 of parametrs except ``enabled`` again.  Once the re-reading is done, this
72 re-reading, DAMON_RECLAIM will be disabled.
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123 Desired level of memory pressure-stall time in microseconds.
127 memory pressure is incurred.  System-wide ``some`` memory PSI in microseconds
130 disabling this auto-tuning feature.
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137 User-specifiable feedback for auto-tuning of the effective quota.
143 this auto-tuning feature.
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156 Free memory rate (per thousand) for the high watermark.
158 If free memory of the system in bytes per thousand bytes is higher than this,
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165 Free memory rate (per thousand) for the middle watermark.
167 If free memory of the system in bytes per thousand bytes is between this and
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174 Free memory rate (per thousand) for the low watermark.
176 If free memory of the system in bytes per thousand bytes is lower than this,
178 watermarks.  In the case, the system falls back to the LRU-list based page
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190 -------------
198 --------------
203 monitoring.  This can be used to set lower-bound of the monitoring quality.
208 --------------
213 monitoring.  This can be used to set upper-bound of the monitoring overhead.
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227 ------------------
236 ---------
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250 -1.
253 ------------------------
258 ---------------------------
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284 nothing if the system's free memory rate is more than 50%, but start the real
286 therefore the free memory rate becomes lower than 20%, it asks DAMON_RECLAIM to
287 do nothing again, so that we can fall back to the LRU-list based page