4 files changed, 773 insertions, 13 deletions

diff --git a/Documentation/vm/Makefile b/Documentation/vm/Makefile
index 6f562f778b28..27479d43a9b0 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 slqbinfo 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: