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)
22     * Bit  57    pte is uffd-wp write-protected (since 5.13) (see
23       Documentation/admin-guide/mm/userfaultfd.rst)
25     * Bits 59-60 zero
26     * Bit  61    page is file-page or shared-anon (since 3.5)
27     * Bit  62    page swapped
31    In 4.0 and 4.1 opens by unprivileged fail with -EPERM.  Starting from
32    4.2 the PFN field is zeroed if the user does not have CAP_SYS_ADMIN.
35    If the page is not present but in swap, then the PFN contains an
56  * ``/proc/kpagecount``.  This file contains a 64-bit count of the number of
58    not track the precise number of times a page part of a larger allocation
64 The page-types tool in the tools/mm directory can be used to query the
67  * ``/proc/kpageflags``.  This file contains a 64-bit set of flags for each
100  * ``/proc/kpagecgroup``.  This file contains a 64-bit inode number of the
107 0 - LOCKED
110 7 - SLAB
114 10 - BUDDY
119 15 - COMPOUND_HEAD
123     pages are hugeTLB pages (Documentation/admin-guide/mm/hugetlbpage.rst),
127 16 - COMPOUND_TAIL
129 17 - HUGE
131 19 - HWPOISON
133 20 - NOPAGE
135 21 - KSM
137 22 - THP
139 23 - OFFLINE
141 24 - ZERO_PAGE
143 25 - IDLE
144     The page has not been accessed since it was marked idle (see
145     Documentation/admin-guide/mm/idle_page_tracking.rst).
147     a PTE. To make sure the flag is up-to-date one has to read
149 26 - PGTABLE
153 ---------------------
155 1 - ERROR
157 3 - UPTODATE
158    The page has up-to-date data.
159    ie. for file backed page: (in-memory data revision >= on-disk one)
160 4 - DIRTY
162    i.e. for file backed page: (in-memory data revision >  on-disk one)
163 8 - WRITEBACK
167 ----------------------
169 5 - LRU
171 6 - ACTIVE
173 18 - UNEVICTABLE
174    The page is in the unevictable (non-)LRU list It is somehow pinned and
175    not a candidate for LRU page reclaims, e.g. ramfs pages,
177 2 - REFERENCED
179 9 - RECLAIM
181 11 - MMAP
183 12 - ANON
184    A memory mapped page that is not part of a file.
185 13 - SWAPCACHE
187 14 - SWAPBACKED
190 The page-types tool in the tools/mm directory can be used to query the
197 swapped out. This makes swapped out pages indistinguishable from never-allocated
202 page is swapped out (i.e. SOFT_DIRTY).
204 In user space, whether the page is present, swapped or none can be deduced with
207 lseek() can differentiate between accessed pages (present or swapped out) and
208 holes (none/non-allocated) by specifying the SEEK_DATA flag on the file where
213 cache) and out of memory (swapped out or none/non-allocated).
218 Reading from any of the files will return -EINVAL if you are not starting
219 the read on an 8-byte boundary (e.g., if you sought an odd number of bytes
220 into the file), or if the size of the read is not a multiple of 8 bytes.
222 Before Linux 3.11 pagemap bits 55-60 were used for "page-shift" (which is
224 after first clear of soft-dirty bits. Since Linux 4.2 they are used for
234 - Scan the address range and get the memory ranges matching the provided criteria.
236 - Write-protect the pages. The ``PM_SCAN_WP_MATCHING`` is used to write-protect
238   non-Async Write Protected pages are found. The ``PM_SCAN_WP_MATCHING`` can be
240 - Both of those operations can be combined into one atomic operation where we can
245 - ``PAGE_IS_WPALLOWED`` - Page has async-write-protection enabled
246 - ``PAGE_IS_WRITTEN`` - Page has been written to from the time it was write protected
247 - ``PAGE_IS_FILE`` - Page is file backed
248 - ``PAGE_IS_PRESENT`` - Page is present in the memory
249 - ``PAGE_IS_SWAPPED`` - Page is in swapped
250 - ``PAGE_IS_PFNZERO`` - Page has zero PFN
251 - ``PAGE_IS_HUGE`` - Page is PMD-mapped THP or Hugetlb backed
252 - ``PAGE_IS_SOFT_DIRTY`` - Page is soft-dirty
262     provided or not.
282 Find pages which have been written, are file backed, not swapped and either
296 The ``PAGE_IS_WRITTEN`` flag can be considered as a better-performing alternative
297 of soft-dirty flag. It doesn't get affected by VMA merging of the kernel and hence
298 the user can find the true soft-dirty pages in case of normal pages. (There may
301 "PAGE_IS_WRITTEN" category is used with uffd write protect-enabled ranges to