summaryrefslogtreecommitdiff
path: root/Documentation/vm
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/vm')
-rw-r--r--Documentation/vm/Makefile2
-rw-r--r--Documentation/vm/balance18
-rw-r--r--Documentation/vm/page-types.c698
-rw-r--r--Documentation/vm/pagemap.txt68
4 files changed, 773 insertions, 13 deletions
diff --git a/Documentation/vm/Makefile b/Documentation/vm/Makefile
index 6f562f778b28..5bd269b3731a 100644
--- a/Documentation/vm/Makefile
+++ b/Documentation/vm/Makefile
@@ -2,7 +2,7 @@
obj- := dummy.o
# List of programs to build
-hostprogs-y := slabinfo
+hostprogs-y := slabinfo page-types
# Tell kbuild to always build the programs
always := $(hostprogs-y)
diff --git a/Documentation/vm/balance b/Documentation/vm/balance
index bd3d31bc4915..c46e68cf9344 100644
--- a/Documentation/vm/balance
+++ b/Documentation/vm/balance
@@ -75,15 +75,15 @@ Page stealing from process memory and shm is done if stealing the page would
alleviate memory pressure on any zone in the page's node that has fallen below
its watermark.
-pages_min/pages_low/pages_high/low_on_memory/zone_wake_kswapd: These are
-per-zone fields, used to determine when a zone needs to be balanced. When
-the number of pages falls below pages_min, the hysteric field low_on_memory
-gets set. This stays set till the number of free pages becomes pages_high.
-When low_on_memory is set, page allocation requests will try to free some
-pages in the zone (providing GFP_WAIT is set in the request). Orthogonal
-to this, is the decision to poke kswapd to free some zone pages. That
-decision is not hysteresis based, and is done when the number of free
-pages is below pages_low; in which case zone_wake_kswapd is also set.
+watemark[WMARK_MIN/WMARK_LOW/WMARK_HIGH]/low_on_memory/zone_wake_kswapd: These
+are per-zone fields, used to determine when a zone needs to be balanced. When
+the number of pages falls below watermark[WMARK_MIN], the hysteric field
+low_on_memory gets set. This stays set till the number of free pages becomes
+watermark[WMARK_HIGH]. When low_on_memory is set, page allocation requests will
+try to free some pages in the zone (providing GFP_WAIT is set in the request).
+Orthogonal to this, is the decision to poke kswapd to free some zone pages.
+That decision is not hysteresis based, and is done when the number of free
+pages is below watermark[WMARK_LOW]; in which case zone_wake_kswapd is also set.
(Good) Ideas that I have heard:
diff --git a/Documentation/vm/page-types.c b/Documentation/vm/page-types.c
new file mode 100644
index 000000000000..0833f44ba16b
--- /dev/null
+++ b/Documentation/vm/page-types.c
@@ -0,0 +1,698 @@
+/*
+ * page-types: Tool for querying page flags
+ *
+ * Copyright (C) 2009 Intel corporation
+ * Copyright (C) 2009 Wu Fengguang <fengguang.wu@intel.com>
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <stdarg.h>
+#include <string.h>
+#include <getopt.h>
+#include <limits.h>
+#include <sys/types.h>
+#include <sys/errno.h>
+#include <sys/fcntl.h>
+
+
+/*
+ * kernel page flags
+ */
+
+#define KPF_BYTES 8
+#define PROC_KPAGEFLAGS "/proc/kpageflags"
+
+/* copied from kpageflags_read() */
+#define KPF_LOCKED 0
+#define KPF_ERROR 1
+#define KPF_REFERENCED 2
+#define KPF_UPTODATE 3
+#define KPF_DIRTY 4
+#define KPF_LRU 5
+#define KPF_ACTIVE 6
+#define KPF_SLAB 7
+#define KPF_WRITEBACK 8
+#define KPF_RECLAIM 9
+#define KPF_BUDDY 10
+
+/* [11-20] new additions in 2.6.31 */
+#define KPF_MMAP 11
+#define KPF_ANON 12
+#define KPF_SWAPCACHE 13
+#define KPF_SWAPBACKED 14
+#define KPF_COMPOUND_HEAD 15
+#define KPF_COMPOUND_TAIL 16
+#define KPF_HUGE 17
+#define KPF_UNEVICTABLE 18
+#define KPF_NOPAGE 20
+
+/* [32-] kernel hacking assistances */
+#define KPF_RESERVED 32
+#define KPF_MLOCKED 33
+#define KPF_MAPPEDTODISK 34
+#define KPF_PRIVATE 35
+#define KPF_PRIVATE_2 36
+#define KPF_OWNER_PRIVATE 37
+#define KPF_ARCH 38
+#define KPF_UNCACHED 39
+
+/* [48-] take some arbitrary free slots for expanding overloaded flags
+ * not part of kernel API
+ */
+#define KPF_READAHEAD 48
+#define KPF_SLOB_FREE 49
+#define KPF_SLUB_FROZEN 50
+#define KPF_SLUB_DEBUG 51
+
+#define KPF_ALL_BITS ((uint64_t)~0ULL)
+#define KPF_HACKERS_BITS (0xffffULL << 32)
+#define KPF_OVERLOADED_BITS (0xffffULL << 48)
+#define BIT(name) (1ULL << KPF_##name)
+#define BITS_COMPOUND (BIT(COMPOUND_HEAD) | BIT(COMPOUND_TAIL))
+
+static char *page_flag_names[] = {
+ [KPF_LOCKED] = "L:locked",
+ [KPF_ERROR] = "E:error",
+ [KPF_REFERENCED] = "R:referenced",
+ [KPF_UPTODATE] = "U:uptodate",
+ [KPF_DIRTY] = "D:dirty",
+ [KPF_LRU] = "l:lru",
+ [KPF_ACTIVE] = "A:active",
+ [KPF_SLAB] = "S:slab",
+ [KPF_WRITEBACK] = "W:writeback",
+ [KPF_RECLAIM] = "I:reclaim",
+ [KPF_BUDDY] = "B:buddy",
+
+ [KPF_MMAP] = "M:mmap",
+ [KPF_ANON] = "a:anonymous",
+ [KPF_SWAPCACHE] = "s:swapcache",
+ [KPF_SWAPBACKED] = "b:swapbacked",
+ [KPF_COMPOUND_HEAD] = "H:compound_head",
+ [KPF_COMPOUND_TAIL] = "T:compound_tail",
+ [KPF_HUGE] = "G:huge",
+ [KPF_UNEVICTABLE] = "u:unevictable",
+ [KPF_NOPAGE] = "n:nopage",
+
+ [KPF_RESERVED] = "r:reserved",
+ [KPF_MLOCKED] = "m:mlocked",
+ [KPF_MAPPEDTODISK] = "d:mappedtodisk",
+ [KPF_PRIVATE] = "P:private",
+ [KPF_PRIVATE_2] = "p:private_2",
+ [KPF_OWNER_PRIVATE] = "O:owner_private",
+ [KPF_ARCH] = "h:arch",
+ [KPF_UNCACHED] = "c:uncached",
+
+ [KPF_READAHEAD] = "I:readahead",
+ [KPF_SLOB_FREE] = "P:slob_free",
+ [KPF_SLUB_FROZEN] = "A:slub_frozen",
+ [KPF_SLUB_DEBUG] = "E:slub_debug",
+};
+
+
+/*
+ * data structures
+ */
+
+static int opt_raw; /* for kernel developers */
+static int opt_list; /* list pages (in ranges) */
+static int opt_no_summary; /* don't show summary */
+static pid_t opt_pid; /* process to walk */
+
+#define MAX_ADDR_RANGES 1024
+static int nr_addr_ranges;
+static unsigned long opt_offset[MAX_ADDR_RANGES];
+static unsigned long opt_size[MAX_ADDR_RANGES];
+
+#define MAX_BIT_FILTERS 64
+static int nr_bit_filters;
+static uint64_t opt_mask[MAX_BIT_FILTERS];
+static uint64_t opt_bits[MAX_BIT_FILTERS];
+
+static int page_size;
+
+#define PAGES_BATCH (64 << 10) /* 64k pages */
+static int kpageflags_fd;
+static uint64_t kpageflags_buf[KPF_BYTES * PAGES_BATCH];
+
+#define HASH_SHIFT 13
+#define HASH_SIZE (1 << HASH_SHIFT)
+#define HASH_MASK (HASH_SIZE - 1)
+#define HASH_KEY(flags) (flags & HASH_MASK)
+
+static unsigned long total_pages;
+static unsigned long nr_pages[HASH_SIZE];
+static uint64_t page_flags[HASH_SIZE];
+
+
+/*
+ * helper functions
+ */
+
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
+#define min_t(type, x, y) ({ \
+ type __min1 = (x); \
+ type __min2 = (y); \
+ __min1 < __min2 ? __min1 : __min2; })
+
+unsigned long pages2mb(unsigned long pages)
+{
+ return (pages * page_size) >> 20;
+}
+
+void fatal(const char *x, ...)
+{
+ va_list ap;
+
+ va_start(ap, x);
+ vfprintf(stderr, x, ap);
+ va_end(ap);
+ exit(EXIT_FAILURE);
+}
+
+
+/*
+ * page flag names
+ */
+
+char *page_flag_name(uint64_t flags)
+{
+ static char buf[65];
+ int present;
+ int i, j;
+
+ for (i = 0, j = 0; i < ARRAY_SIZE(page_flag_names); i++) {
+ present = (flags >> i) & 1;
+ if (!page_flag_names[i]) {
+ if (present)
+ fatal("unkown flag bit %d\n", i);
+ continue;
+ }
+ buf[j++] = present ? page_flag_names[i][0] : '_';
+ }
+
+ return buf;
+}
+
+char *page_flag_longname(uint64_t flags)
+{
+ static char buf[1024];
+ int i, n;
+
+ for (i = 0, n = 0; i < ARRAY_SIZE(page_flag_names); i++) {
+ if (!page_flag_names[i])
+ continue;
+ if ((flags >> i) & 1)
+ n += snprintf(buf + n, sizeof(buf) - n, "%s,",
+ page_flag_names[i] + 2);
+ }
+ if (n)
+ n--;
+ buf[n] = '\0';
+
+ return buf;
+}
+
+
+/*
+ * page list and summary
+ */
+
+void show_page_range(unsigned long offset, uint64_t flags)
+{
+ static uint64_t flags0;
+ static unsigned long index;
+ static unsigned long count;
+
+ if (flags == flags0 && offset == index + count) {
+ count++;
+ return;
+ }
+
+ if (count)
+ printf("%lu\t%lu\t%s\n",
+ index, count, page_flag_name(flags0));
+
+ flags0 = flags;
+ index = offset;
+ count = 1;
+}
+
+void show_page(unsigned long offset, uint64_t flags)
+{
+ printf("%lu\t%s\n", offset, page_flag_name(flags));
+}
+
+void show_summary(void)
+{
+ int i;
+
+ printf(" flags\tpage-count MB"
+ " symbolic-flags\t\t\tlong-symbolic-flags\n");
+
+ for (i = 0; i < ARRAY_SIZE(nr_pages); i++) {
+ if (nr_pages[i])
+ printf("0x%016llx\t%10lu %8lu %s\t%s\n",
+ (unsigned long long)page_flags[i],
+ nr_pages[i],
+ pages2mb(nr_pages[i]),
+ page_flag_name(page_flags[i]),
+ page_flag_longname(page_flags[i]));
+ }
+
+ printf(" total\t%10lu %8lu\n",
+ total_pages, pages2mb(total_pages));
+}
+
+
+/*
+ * page flag filters
+ */
+
+int bit_mask_ok(uint64_t flags)
+{
+ int i;
+
+ for (i = 0; i < nr_bit_filters; i++) {
+ if (opt_bits[i] == KPF_ALL_BITS) {
+ if ((flags & opt_mask[i]) == 0)
+ return 0;
+ } else {
+ if ((flags & opt_mask[i]) != opt_bits[i])
+ return 0;
+ }
+ }
+
+ return 1;
+}
+
+uint64_t expand_overloaded_flags(uint64_t flags)
+{
+ /* SLOB/SLUB overload several page flags */
+ if (flags & BIT(SLAB)) {
+ if (flags & BIT(PRIVATE))
+ flags ^= BIT(PRIVATE) | BIT(SLOB_FREE);
+ if (flags & BIT(ACTIVE))
+ flags ^= BIT(ACTIVE) | BIT(SLUB_FROZEN);
+ if (flags & BIT(ERROR))
+ flags ^= BIT(ERROR) | BIT(SLUB_DEBUG);
+ }
+
+ /* PG_reclaim is overloaded as PG_readahead in the read path */
+ if ((flags & (BIT(RECLAIM) | BIT(WRITEBACK))) == BIT(RECLAIM))
+ flags ^= BIT(RECLAIM) | BIT(READAHEAD);
+
+ return flags;
+}
+
+uint64_t well_known_flags(uint64_t flags)
+{
+ /* hide flags intended only for kernel hacker */
+ flags &= ~KPF_HACKERS_BITS;
+
+ /* hide non-hugeTLB compound pages */
+ if ((flags & BITS_COMPOUND) && !(flags & BIT(HUGE)))
+ flags &= ~BITS_COMPOUND;
+
+ return flags;
+}
+
+
+/*
+ * page frame walker
+ */
+
+int hash_slot(uint64_t flags)
+{
+ int k = HASH_KEY(flags);
+ int i;
+
+ /* Explicitly reserve slot 0 for flags 0: the following logic
+ * cannot distinguish an unoccupied slot from slot (flags==0).
+ */
+ if (flags == 0)
+ return 0;
+
+ /* search through the remaining (HASH_SIZE-1) slots */
+ for (i = 1; i < ARRAY_SIZE(page_flags); i++, k++) {
+ if (!k || k >= ARRAY_SIZE(page_flags))
+ k = 1;
+ if (page_flags[k] == 0) {
+ page_flags[k] = flags;
+ return k;
+ }
+ if (page_flags[k] == flags)
+ return k;
+ }
+
+ fatal("hash table full: bump up HASH_SHIFT?\n");
+ exit(EXIT_FAILURE);
+}
+
+void add_page(unsigned long offset, uint64_t flags)
+{
+ flags = expand_overloaded_flags(flags);
+
+ if (!opt_raw)
+ flags = well_known_flags(flags);
+
+ if (!bit_mask_ok(flags))
+ return;
+
+ if (opt_list == 1)
+ show_page_range(offset, flags);
+ else if (opt_list == 2)
+ show_page(offset, flags);
+
+ nr_pages[hash_slot(flags)]++;
+ total_pages++;
+}
+
+void walk_pfn(unsigned long index, unsigned long count)
+{
+ unsigned long batch;
+ unsigned long n;
+ unsigned long i;
+
+ if (index > ULONG_MAX / KPF_BYTES)
+ fatal("index overflow: %lu\n", index);
+
+ lseek(kpageflags_fd, index * KPF_BYTES, SEEK_SET);
+
+ while (count) {
+ batch = min_t(unsigned long, count, PAGES_BATCH);
+ n = read(kpageflags_fd, kpageflags_buf, batch * KPF_BYTES);
+ if (n == 0)
+ break;
+ if (n < 0) {
+ perror(PROC_KPAGEFLAGS);
+ exit(EXIT_FAILURE);
+ }
+
+ if (n % KPF_BYTES != 0)
+ fatal("partial read: %lu bytes\n", n);
+ n = n / KPF_BYTES;
+
+ for (i = 0; i < n; i++)
+ add_page(index + i, kpageflags_buf[i]);
+
+ index += batch;
+ count -= batch;
+ }
+}
+
+void walk_addr_ranges(void)
+{
+ int i;
+
+ kpageflags_fd = open(PROC_KPAGEFLAGS, O_RDONLY);
+ if (kpageflags_fd < 0) {
+ perror(PROC_KPAGEFLAGS);
+ exit(EXIT_FAILURE);
+ }
+
+ if (!nr_addr_ranges)
+ walk_pfn(0, ULONG_MAX);
+
+ for (i = 0; i < nr_addr_ranges; i++)
+ walk_pfn(opt_offset[i], opt_size[i]);
+
+ close(kpageflags_fd);
+}
+
+
+/*
+ * user interface
+ */
+
+const char *page_flag_type(uint64_t flag)
+{
+ if (flag & KPF_HACKERS_BITS)
+ return "(r)";
+ if (flag & KPF_OVERLOADED_BITS)
+ return "(o)";
+ return " ";
+}
+
+void usage(void)
+{
+ int i, j;
+
+ printf(
+"page-types [options]\n"
+" -r|--raw Raw mode, for kernel developers\n"
+" -a|--addr addr-spec Walk a range of pages\n"
+" -b|--bits bits-spec Walk pages with specified bits\n"
+#if 0 /* planned features */
+" -p|--pid pid Walk process address space\n"
+" -f|--file filename Walk file address space\n"
+#endif
+" -l|--list Show page details in ranges\n"
+" -L|--list-each Show page details one by one\n"
+" -N|--no-summary Don't show summay info\n"
+" -h|--help Show this usage message\n"
+"addr-spec:\n"
+" N one page at offset N (unit: pages)\n"
+" N+M pages range from N to N+M-1\n"
+" N,M pages range from N to M-1\n"
+" N, pages range from N to end\n"
+" ,M pages range from 0 to M\n"
+"bits-spec:\n"
+" bit1,bit2 (flags & (bit1|bit2)) != 0\n"
+" bit1,bit2=bit1 (flags & (bit1|bit2)) == bit1\n"
+" bit1,~bit2 (flags & (bit1|bit2)) == bit1\n"
+" =bit1,bit2 flags == (bit1|bit2)\n"
+"bit-names:\n"
+ );
+
+ for (i = 0, j = 0; i < ARRAY_SIZE(page_flag_names); i++) {
+ if (!page_flag_names[i])
+ continue;
+ printf("%16s%s", page_flag_names[i] + 2,
+ page_flag_type(1ULL << i));
+ if (++j > 3) {
+ j = 0;
+ putchar('\n');
+ }
+ }
+ printf("\n "
+ "(r) raw mode bits (o) overloaded bits\n");
+}
+
+unsigned long long parse_number(const char *str)
+{
+ unsigned long long n;
+
+ n = strtoll(str, NULL, 0);
+
+ if (n == 0 && str[0] != '0')
+ fatal("invalid name or number: %s\n", str);
+
+ return n;
+}
+
+void parse_pid(const char *str)
+{
+ opt_pid = parse_number(str);
+}
+
+void parse_file(const char *name)
+{
+}
+
+void add_addr_range(unsigned long offset, unsigned long size)
+{
+ if (nr_addr_ranges >= MAX_ADDR_RANGES)
+ fatal("too much addr ranges\n");
+
+ opt_offset[nr_addr_ranges] = offset;
+ opt_size[nr_addr_ranges] = size;
+ nr_addr_ranges++;
+}
+
+void parse_addr_range(const char *optarg)
+{
+ unsigned long offset;
+ unsigned long size;
+ char *p;
+
+ p = strchr(optarg, ',');
+ if (!p)
+ p = strchr(optarg, '+');
+
+ if (p == optarg) {
+ offset = 0;
+ size = parse_number(p + 1);
+ } else if (p) {
+ offset = parse_number(optarg);
+ if (p[1] == '\0')
+ size = ULONG_MAX;
+ else {
+ size = parse_number(p + 1);
+ if (*p == ',') {
+ if (size < offset)
+ fatal("invalid range: %lu,%lu\n",
+ offset, size);
+ size -= offset;
+ }
+ }
+ } else {
+ offset = parse_number(optarg);
+ size = 1;
+ }
+
+ add_addr_range(offset, size);
+}
+
+void add_bits_filter(uint64_t mask, uint64_t bits)
+{
+ if (nr_bit_filters >= MAX_BIT_FILTERS)
+ fatal("too much bit filters\n");
+
+ opt_mask[nr_bit_filters] = mask;
+ opt_bits[nr_bit_filters] = bits;
+ nr_bit_filters++;
+}
+
+uint64_t parse_flag_name(const char *str, int len)
+{
+ int i;
+
+ if (!*str || !len)
+ return 0;
+
+ if (len <= 8 && !strncmp(str, "compound", len))
+ return BITS_COMPOUND;
+
+ for (i = 0; i < ARRAY_SIZE(page_flag_names); i++) {
+ if (!page_flag_names[i])
+ continue;
+ if (!strncmp(str, page_flag_names[i] + 2, len))
+ return 1ULL << i;
+ }
+
+ return parse_number(str);
+}
+
+uint64_t parse_flag_names(const char *str, int all)
+{
+ const char *p = str;
+ uint64_t flags = 0;
+
+ while (1) {
+ if (*p == ',' || *p == '=' || *p == '\0') {
+ if ((*str != '~') || (*str == '~' && all && *++str))
+ flags |= parse_flag_name(str, p - str);
+ if (*p != ',')
+ break;
+ str = p + 1;
+ }
+ p++;
+ }
+
+ return flags;
+}
+
+void parse_bits_mask(const char *optarg)
+{
+ uint64_t mask;
+ uint64_t bits;
+ const char *p;
+
+ p = strchr(optarg, '=');
+ if (p == optarg) {
+ mask = KPF_ALL_BITS;
+ bits = parse_flag_names(p + 1, 0);
+ } else if (p) {
+ mask = parse_flag_names(optarg, 0);
+ bits = parse_flag_names(p + 1, 0);
+ } else if (strchr(optarg, '~')) {
+ mask = parse_flag_names(optarg, 1);
+ bits = parse_flag_names(optarg, 0);
+ } else {
+ mask = parse_flag_names(optarg, 0);
+ bits = KPF_ALL_BITS;
+ }
+
+ add_bits_filter(mask, bits);
+}
+
+
+struct option opts[] = {
+ { "raw" , 0, NULL, 'r' },
+ { "pid" , 1, NULL, 'p' },
+ { "file" , 1, NULL, 'f' },
+ { "addr" , 1, NULL, 'a' },
+ { "bits" , 1, NULL, 'b' },
+ { "list" , 0, NULL, 'l' },
+ { "list-each" , 0, NULL, 'L' },
+ { "no-summary", 0, NULL, 'N' },
+ { "help" , 0, NULL, 'h' },
+ { NULL , 0, NULL, 0 }
+};
+
+int main(int argc, char *argv[])
+{
+ int c;
+
+ page_size = getpagesize();
+
+ while ((c = getopt_long(argc, argv,
+ "rp:f:a:b:lLNh", opts, NULL)) != -1) {
+ switch (c) {
+ case 'r':
+ opt_raw = 1;
+ break;
+ case 'p':
+ parse_pid(optarg);
+ break;
+ case 'f':
+ parse_file(optarg);
+ break;
+ case 'a':
+ parse_addr_range(optarg);
+ break;
+ case 'b':
+ parse_bits_mask(optarg);
+ break;
+ case 'l':
+ opt_list = 1;
+ break;
+ case 'L':
+ opt_list = 2;
+ break;
+ case 'N':
+ opt_no_summary = 1;
+ break;
+ case 'h':
+ usage();
+ exit(0);
+ default:
+ usage();
+ exit(1);
+ }
+ }
+
+ if (opt_list == 1)
+ printf("offset\tcount\tflags\n");
+ if (opt_list == 2)
+ printf("offset\tflags\n");
+
+ walk_addr_ranges();
+
+ if (opt_list == 1)
+ show_page_range(0, 0); /* drain the buffer */
+
+ if (opt_no_summary)
+ return 0;
+
+ if (opt_list)
+ printf("\n\n");
+
+ show_summary();
+
+ return 0;
+}
diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt
index ce72c0fe6177..600a304a828c 100644
--- a/Documentation/vm/pagemap.txt
+++ b/Documentation/vm/pagemap.txt
@@ -12,9 +12,9 @@ There are three components to pagemap:
value for each virtual page, containing the following data (from
fs/proc/task_mmu.c, above pagemap_read):
- * Bits 0-55 page frame number (PFN) if present
+ * Bits 0-54 page frame number (PFN) if present
* Bits 0-4 swap type if swapped
- * Bits 5-55 swap offset if swapped
+ * Bits 5-54 swap offset if swapped
* Bits 55-60 page shift (page size = 1<<page shift)
* Bit 61 reserved for future use
* Bit 62 page swapped
@@ -36,7 +36,7 @@ There are three components to pagemap:
* /proc/kpageflags. This file contains a 64-bit set of flags for each
page, indexed by PFN.
- The flags are (from fs/proc/proc_misc, above kpageflags_read):
+ The flags are (from fs/proc/page.c, above kpageflags_read):
0. LOCKED
1. ERROR
@@ -49,6 +49,68 @@ There are three components to pagemap:
8. WRITEBACK
9. RECLAIM
10. BUDDY
+ 11. MMAP
+ 12. ANON
+ 13. SWAPCACHE
+ 14. SWAPBACKED
+ 15. COMPOUND_HEAD
+ 16. COMPOUND_TAIL
+ 16. HUGE
+ 18. UNEVICTABLE
+ 20. NOPAGE
+
+Short descriptions to the page flags:
+
+ 0. LOCKED
+ page is being locked for exclusive access, eg. by undergoing read/write IO
+
+ 7. SLAB
+ page is managed by the SLAB/SLOB/SLUB/SLQB kernel memory allocator
+ When compound page is used, SLUB/SLQB will only set this flag on the head
+ page; SLOB will not flag it at all.
+
+10. BUDDY
+ a free memory block managed by the buddy system allocator
+ The buddy system organizes free memory in blocks of various orders.
+ An order N block has 2^N physically contiguous pages, with the BUDDY flag
+ set for and _only_ for the first page.
+
+15. COMPOUND_HEAD
+16. COMPOUND_TAIL
+ A compound page with order N consists of 2^N physically contiguous pages.
+ A compound page with order 2 takes the form of "HTTT", where H donates its
+ head page and T donates its tail page(s). The major consumers of compound
+ pages are hugeTLB pages (Documentation/vm/hugetlbpage.txt), the SLUB etc.
+ memory allocators and various device drivers. However in this interface,
+ only huge/giga pages are made visible to end users.
+17. HUGE
+ this is an integral part of a HugeTLB page
+
+20. NOPAGE
+ no page frame exists at the requested address
+
+ [IO related page flags]
+ 1. ERROR IO error occurred
+ 3. UPTODATE page has up-to-date data
+ ie. for file backed page: (in-memory data revision >= on-disk one)
+ 4. DIRTY page has been written to, hence contains new data
+ ie. for file backed page: (in-memory data revision > on-disk one)
+ 8. WRITEBACK page is being synced to disk
+
+ [LRU related page flags]
+ 5. LRU page is in one of the LRU lists
+ 6. ACTIVE page is in the active LRU list
+18. UNEVICTABLE page is in the unevictable (non-)LRU list
+ It is somehow pinned and not a candidate for LRU page reclaims,
+ eg. ramfs pages, shmctl(SHM_LOCK) and mlock() memory segments
+ 2. REFERENCED page has been referenced since last LRU list enqueue/requeue
+ 9. RECLAIM page will be reclaimed soon after its pageout IO completed
+11. MMAP a memory mapped page
+12. ANON a memory mapped page that is not part of a file
+13. SWAPCACHE page is mapped to swap space, ie. has an associated swap entry
+14. SWAPBACKED page is backed by swap/RAM
+
+The page-types tool in this directory can be used to query the above flags.
Using pagemap to do something useful:
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-22 09:10:12 +0000