From c638072107f52ec35f292c97b6f3df9b9f2ed87d Mon Sep 17 00:00:00 2001 From: SeongJae Park Date: Fri, 5 Nov 2021 13:47:03 -0700 Subject: Docs/DAMON: document physical memory monitoring support This updates the DAMON documents for the physical memory address space monitoring support. Link: https://lkml.kernel.org/r/20211012205711.29216-8-sj@kernel.org Signed-off-by: SeongJae Park Cc: Amit Shah Cc: Benjamin Herrenschmidt Cc: Brendan Higgins Cc: David Hildenbrand Cc: David Rienjes Cc: David Woodhouse Cc: Greg Thelen Cc: Jonathan Cameron Cc: Jonathan Corbet Cc: Leonard Foerster Cc: Marco Elver Cc: Markus Boehme Cc: Shakeel Butt Cc: Shuah Khan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/vm/damon/design.rst | 29 ++++++++++++++++++----------- Documentation/vm/damon/faq.rst | 5 ++--- 2 files changed, 20 insertions(+), 14 deletions(-) (limited to 'Documentation/vm') diff --git a/Documentation/vm/damon/design.rst b/Documentation/vm/damon/design.rst index b05159c295f4..210f0f50efd8 100644 --- a/Documentation/vm/damon/design.rst +++ b/Documentation/vm/damon/design.rst @@ -35,13 +35,17 @@ two parts: 1. Identification of the monitoring target address range for the address space. 2. Access check of specific address range in the target space. -DAMON currently provides the implementation of the primitives for only the -virtual address spaces. Below two subsections describe how it works. +DAMON currently provides the implementations of the primitives for the physical +and virtual address spaces. Below two subsections describe how those work. VMA-based Target Address Range Construction ------------------------------------------- +This is only for the virtual address space primitives implementation. That for +the physical address space simply asks users to manually set the monitoring +target address ranges. + Only small parts in the super-huge virtual address space of the processes are mapped to the physical memory and accessed. Thus, tracking the unmapped address regions is just wasteful. However, because DAMON can deal with some @@ -71,15 +75,18 @@ to make a reasonable trade-off. Below shows this in detail:: PTE Accessed-bit Based Access Check ----------------------------------- -The implementation for the virtual address space uses PTE Accessed-bit for -basic access checks. It finds the relevant PTE Accessed bit from the address -by walking the page table for the target task of the address. In this way, the -implementation finds and clears the bit for next sampling target address and -checks whether the bit set again after one sampling period. This could disturb -other kernel subsystems using the Accessed bits, namely Idle page tracking and -the reclaim logic. To avoid such disturbances, DAMON makes it mutually -exclusive with Idle page tracking and uses ``PG_idle`` and ``PG_young`` page -flags to solve the conflict with the reclaim logic, as Idle page tracking does. +Both of the implementations for physical and virtual address spaces use PTE +Accessed-bit for basic access checks. Only one difference is the way of +finding the relevant PTE Accessed bit(s) from the address. While the +implementation for the virtual address walks the page table for the target task +of the address, the implementation for the physical address walks every page +table having a mapping to the address. In this way, the implementations find +and clear the bit(s) for next sampling target address and checks whether the +bit(s) set again after one sampling period. This could disturb other kernel +subsystems using the Accessed bits, namely Idle page tracking and the reclaim +logic. To avoid such disturbances, DAMON makes it mutually exclusive with Idle +page tracking and uses ``PG_idle`` and ``PG_young`` page flags to solve the +conflict with the reclaim logic, as Idle page tracking does. Address Space Independent Core Mechanisms diff --git a/Documentation/vm/damon/faq.rst b/Documentation/vm/damon/faq.rst index cb3d8b585a8b..11aea40eb328 100644 --- a/Documentation/vm/damon/faq.rst +++ b/Documentation/vm/damon/faq.rst @@ -36,10 +36,9 @@ constructions and actual access checks can be implemented and configured on the DAMON core by the users. In this way, DAMON users can monitor any address space with any access check technique. -Nonetheless, DAMON provides vma tracking and PTE Accessed bit check based +Nonetheless, DAMON provides vma/rmap tracking and PTE Accessed bit check based implementations of the address space dependent functions for the virtual memory -by default, for a reference and convenient use. In near future, we will -provide those for physical memory address space. +and the physical memory by default, for a reference and convenient use. Can I simply monitor page granularity? -- cgit v1.2.3