admin-guide/mm/pagemap.rst

12    physical frame each virtual page is mapped to.  It contains one 64-bit
16     * Bits 0-54  page frame number (PFN) if present
17     * Bits 0-4   swap type if swapped
18     * Bits 5-54  swap offset if swapped
19     * Bit  55    pte is soft-dirty (see
20       Documentation/admin-guide/mm/soft-dirty.rst)
21     * Bit  56    page exclusively mapped (since 4.2)
22     * Bit  57    pte is uffd-wp write-protected (since 5.13) (see
23       Documentation/admin-guide/mm/userfaultfd.rst)
24     * Bits 58-60 zero
25     * Bit  61    page is file-page or shared-anon (since 3.5)
30    In 4.0 and 4.1 opens by unprivileged fail with -EPERM.  Starting from
37    precisely which pages are mapped (or in swap) and comparing mapped
41    determine which areas of memory are actually mapped and llseek to
44  * ``/proc/kpagecount``.  This file contains a 64-bit count of the number of
45    times each page is mapped, indexed by PFN.
47 The page-types tool in the tools/mm directory can be used to query the
48 number of times a page is mapped.
50  * ``/proc/kpageflags``.  This file contains a 64-bit set of flags for each
83  * ``/proc/kpagecgroup``.  This file contains a 64-bit inode number of the
84    memory cgroup each page is charged to, indexed by PFN. Only available when
90 0 - LOCKED
93 7 - SLAB
94    The page is managed by the SLAB/SLUB kernel memory allocator.
97 10 - BUDDY
98     A free memory block managed by the buddy system allocator.
99     The buddy system organizes free memory in blocks of various orders.
102 15 - COMPOUND_HEAD
106     pages are hugeTLB pages (Documentation/admin-guide/mm/hugetlbpage.rst),
107     the SLUB etc.  memory allocators and various device drivers.
110 16 - COMPOUND_TAIL
112 17 - HUGE
114 19 - HWPOISON
115     Hardware detected memory corruption on this page: don't touch the data!
116 20 - NOPAGE
118 21 - KSM
119     Identical memory pages dynamically shared between one or more processes.
120 22 - THP
122 23 - OFFLINE
124 24 - ZERO_PAGE
126 25 - IDLE
128     Documentation/admin-guide/mm/idle_page_tracking.rst).
130     a PTE. To make sure the flag is up-to-date one has to read
132 26 - PGTABLE
136 ---------------------
138 1 - ERROR
140 3 - UPTODATE
141    The page has up-to-date data.
142    ie. for file backed page: (in-memory data revision >= on-disk one)
143 4 - DIRTY
145    i.e. for file backed page: (in-memory data revision >  on-disk one)
146 8 - WRITEBACK
150 ----------------------
152 5 - LRU
154 6 - ACTIVE
156 18 - UNEVICTABLE
157    The page is in the unevictable (non-)LRU list It is somehow pinned and
159    shmctl(SHM_LOCK) and mlock() memory segments.
160 2 - REFERENCED
162 9 - RECLAIM
164 11 - MMAP
165    A memory mapped page.
166 12 - ANON
167    A memory mapped page that is not part of a file.
168 13 - SWAPCACHE
169    The page is mapped to swap space, i.e. has an associated swap entry.
170 14 - SWAPBACKED
173 The page-types tool in the tools/mm directory can be used to query the
179 The general procedure for using pagemap to find out about a process' memory
182  1. Read ``/proc/pid/maps`` to determine which parts of the memory space are
183     mapped to what.
184  2. Select the maps you are interested in -- all of them, or a particular
192 memory that a process is using that is not shared with any other process,
197 Exceptions for Shared Memory
201 swapped out. This makes swapped out pages indistinguishable from never-allocated
212 holes (none/non-allocated) by specifying the SEEK_DATA flag on the file where
216 mincore() can differentiate between pages in memory (present, including swap
217 cache) and out of memory (swapped out or none/non-allocated).
222 Reading from any of the files will return -EINVAL if you are not starting
223 the read on an 8-byte boundary (e.g., if you sought an odd number of bytes
226 Before Linux 3.11 pagemap bits 55-60 were used for "page-shift" (which is
228 after first clear of soft-dirty bits. Since Linux 4.2 they are used for