admin-guide/mm/idle_page_tracking.rst

9 accessed by a workload and which are idle. This information can be useful for
12 or deciding where to place the workload within a compute cluster.
25 The file implements a bitmap where each bit corresponds to a memory page. The
27 mapped to bit #i%64 of array element #i/64, byte order is native. When a bit is
33 To mark a page idle one has to set the bit corresponding to
37 Only accesses to user memory pages are tracked. These are pages mapped to a
39 page types (e.g. SLAB pages) an attempt to mark a page idle is silently ignored,
47 if the size of the read/write is not a multiple of 8 bytes. Writing to
50 That said, in order to estimate the amount of pages that are not used by a
55     ``/proc/pid/pagemap`` if the workload is represented by a process, or by
57     is placed in a memory cgroup.
81 considered referenced if it has been recently accessed via a process address
86  - a userspace process reads or writes a page using a system call (e.g. read(2)
89  - a page that is used for storing filesystem buffers is read or written,
90    because a process needs filesystem metadata stored in it (e.g. lists a
93  - a page is accessed by a device driver using get_user_pages()
95 When a dirty page is written to swap or disk as a result of memory reclaim or
98 The idle memory tracking feature adds a new page flag, the Idle flag. This flag
101 section), and cleared automatically whenever a page is referenced as defined
104 When a page is marked idle, the Accessed bit must be cleared in all PTEs it is
106 from a process address space. To avoid interference with the reclaimer, which,
109 cleared as a result of setting or updating a page's Idle flag, the Young flag
111 Accessed bit and therefore will consider such a page as referenced.
115 ignored. That means it will ignore a user memory page if it is isolated, but