51 lines
2.2 KiB
ReStructuredText
51 lines
2.2 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0
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==========================
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Frequently Asked Questions
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==========================
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Why a new subsystem, instead of extending perf or other user space tools?
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=========================================================================
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First, because it needs to be lightweight as much as possible so that it can be
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used online, any unnecessary overhead such as kernel - user space context
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switching cost should be avoided. Second, DAMON aims to be used by other
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programs including the kernel. Therefore, having a dependency on specific
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tools like perf is not desirable. These are the two biggest reasons why DAMON
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is implemented in the kernel space.
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Can 'idle pages tracking' or 'perf mem' substitute DAMON?
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=========================================================
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Idle page tracking is a low level primitive for access check of the physical
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address space. 'perf mem' is similar, though it can use sampling to minimize
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the overhead. On the other hand, DAMON is a higher-level framework for the
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monitoring of various address spaces. It is focused on memory management
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optimization and provides sophisticated accuracy/overhead handling mechanisms.
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Therefore, 'idle pages tracking' and 'perf mem' could provide a subset of
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DAMON's output, but cannot substitute DAMON.
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Does DAMON support virtual memory only?
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=======================================
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No. The core of the DAMON is address space independent. The address space
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specific monitoring operations including monitoring target regions
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constructions and actual access checks can be implemented and configured on the
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DAMON core by the users. In this way, DAMON users can monitor any address
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space with any access check technique.
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Nonetheless, DAMON provides vma/rmap tracking and PTE Accessed bit check based
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implementations of the address space dependent functions for the virtual memory
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and the physical memory by default, for a reference and convenient use.
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Can I simply monitor page granularity?
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======================================
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Yes. You can do so by setting the ``min_nr_regions`` attribute higher than the
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working set size divided by the page size. Because the monitoring target
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regions size is forced to be ``>=page size``, the region split will make no
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effect.
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