journal: implement generic sharable mmap caching logic

instead of having one simple per-file cache implement an more
comprehensive one that works for multiple files and can actually
maintain multiple maps per file and per object type.

11 files changed, 716 insertions, 154 deletions

diff --git a/Makefile.am b/Makefile.am
index 837bc6c5b2..c90867c8da 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -2308,17 +2308,9 @@ EXTRA_DIST += \
 systemd_journald_SOURCES = \
 	src/journal/journald.c \
 	src/journal/journald.h \
-	src/journal/sd-journal.c \
-	src/journal/journal-file.c \
-	src/journal/journal-file.h \
-	src/journal/lookup3.c \
-	src/journal/lookup3.h \
 	src/journal/journal-rate-limit.c \
 	src/journal/journal-rate-limit.h \
-	src/journal/sparse-endian.h \
-	src/journal/journal-def.h \
-	src/journal/journal-internal.h \
-	src/journal/compress.h
+	src/journal/journal-internal.h
 
 nodist_systemd_journald_SOURCES = \
 	src/journal/journald-gperf.c
@@ -2394,9 +2386,18 @@ test_journal_stream_LDADD = \
 
 libsystemd_journal_la_SOURCES = \
 	src/journal/sd-journal.c \
+	src/systemd/sd-journal.h \
 	src/journal/journal-file.c \
+	src/journal/journal-file.h \
 	src/journal/lookup3.c \
-	src/journal/journal-send.c
+	src/journal/lookup3.h \
+	src/journal/journal-send.c \
+	src/journal/journal-send.h \
+	src/journal/sparse-endian.h \
+	src/journal/journal-def.h \
+	src/journal/compress.h \
+	src/journal/mmap-cache.c \
+	src/journal/mmap-cache.h
 
 libsystemd_journal_la_CFLAGS = \
 	$(AM_CFLAGS) \
diff --git a/src/journal/journal-file.c b/src/journal/journal-file.c
index 9235e5fea2..1f5e04d791 100644
--- a/src/journal/journal-file.c
+++ b/src/journal/journal-file.c
@@ -36,8 +36,6 @@
 #define DEFAULT_DATA_HASH_TABLE_SIZE (2047ULL*sizeof(HashItem))
 #define DEFAULT_FIELD_HASH_TABLE_SIZE (333ULL*sizeof(HashItem))
 
-#define DEFAULT_WINDOW_SIZE (8ULL*1024ULL*1024ULL)
-
 #define COMPRESSION_SIZE_THRESHOLD (512ULL)
 
 /* This is the minimum journal file size */
@@ -71,8 +69,6 @@ static int journal_file_maybe_append_tag(JournalFile *f, uint64_t realtime);
 static int journal_file_hmac_put_object(JournalFile *f, int type, uint64_t p);
 
 void journal_file_close(JournalFile *f) {
-        int t;
-
         assert(f);
 
         /* Write the final tag */
@@ -80,9 +76,8 @@ void journal_file_close(JournalFile *f) {
                 journal_file_append_tag(f);
 
         /* Sync everything to disk, before we mark the file offline */
-        for (t = 0; t < _WINDOW_MAX; t++)
-                if (f->windows[t].ptr)
-                        munmap(f->windows[t].ptr, f->windows[t].size);
+        if (f->mmap && f->fd >= 0)
+                mmap_cache_close_fd(f->mmap, f->fd);
 
         if (f->writable && f->fd >= 0)
                 fdatasync(f->fd);
@@ -100,6 +95,9 @@ void journal_file_close(JournalFile *f) {
 
         free(f->path);
 
+        if (f->mmap)
+                mmap_cache_unref(f->mmap);
+
 #ifdef HAVE_XZ
         free(f->compress_buffer);
 #endif
@@ -305,59 +303,11 @@ static int journal_file_allocate(JournalFile *f, uint64_t offset, uint64_t size)
         return 0;
 }
 
-static int journal_file_map(
-                JournalFile *f,
-                uint64_t offset,
-                uint64_t size,
-                void **_window,
-                uint64_t *_woffset,
-                uint64_t *_wsize,
-                void **ret) {
-
-        uint64_t woffset, wsize;
-        void *window;
-
+static int journal_file_move_to(JournalFile *f, int context, uint64_t offset, uint64_t size, void **ret) {
         assert(f);
-        assert(size > 0);
         assert(ret);
 
-        woffset = offset & ~((uint64_t) page_size() - 1ULL);
-        wsize = size + (offset - woffset);
-        wsize = PAGE_ALIGN(wsize);
-
         /* Avoid SIGBUS on invalid accesses */
-        if (woffset + wsize > (uint64_t) PAGE_ALIGN(f->last_stat.st_size))
-                return -EADDRNOTAVAIL;
-
-        window = mmap(NULL, wsize, f->prot, MAP_SHARED, f->fd, woffset);
-        if (window == MAP_FAILED)
-                return -errno;
-
-        if (_window)
-                *_window = window;
-
-        if (_woffset)
-                *_woffset = woffset;
-
-        if (_wsize)
-                *_wsize = wsize;
-
-        *ret = (uint8_t*) window + (offset - woffset);
-
-        return 0;
-}
-
-static int journal_file_move_to(JournalFile *f, int wt, uint64_t offset, uint64_t size, void **ret) {
-        void *p = NULL;
-        uint64_t delta;
-        int r;
-        Window *w;
-
-        assert(f);
-        assert(ret);
-        assert(wt >= 0);
-        assert(wt < _WINDOW_MAX);
-
         if (offset + size > (uint64_t) f->last_stat.st_size) {
                 /* Hmm, out of range? Let's refresh the fstat() data
                  * first, before we trust that check. */
@@ -367,57 +317,7 @@ static int journal_file_move_to(JournalFile *f, int wt, uint64_t offset, uint64_
                         return -EADDRNOTAVAIL;
         }
 
-        w = f->windows + wt;
-
-        if (_likely_(w->ptr &&
-                     w->offset <= offset &&
-                     w->offset + w->size >= offset + size)) {
-
-                *ret = (uint8_t*) w->ptr + (offset - w->offset);
-                return 0;
-        }
-
-        if (w->ptr) {
-                if (munmap(w->ptr, w->size) < 0)
-                        return -errno;
-
-                w->ptr = NULL;
-                w->size = w->offset = 0;
-        }
-
-        if (size < DEFAULT_WINDOW_SIZE) {
-                /* If the default window size is larger then what was
-                 * asked for extend the mapping a bit in the hope to
-                 * minimize needed remappings later on. We add half
-                 * the window space before and half behind the
-                 * requested mapping */
-
-                delta = (DEFAULT_WINDOW_SIZE - size) / 2;
-
-                if (delta > offset)
-                        delta = offset;
-
-                offset -= delta;
-                size = DEFAULT_WINDOW_SIZE;
-        } else
-                delta = 0;
-
-        if (offset + size > (uint64_t) f->last_stat.st_size)
-                size = (uint64_t) f->last_stat.st_size - offset;
-
-        if (size <= 0)
-                return -EADDRNOTAVAIL;
-
-        r = journal_file_map(f,
-                             offset, size,
-                             &w->ptr, &w->offset, &w->size,
-                             &p);
-
-        if (r < 0)
-                return r;
-
-        *ret = (uint8_t*) p + delta;
-        return 0;
+        return mmap_cache_get(f->mmap, f->fd, f->prot, context, offset, size, ret);
 }
 
 static bool verify_hash(Object *o) {
@@ -437,17 +337,38 @@ static bool verify_hash(Object *o) {
         return h1 == h2;
 }
 
+static uint64_t minimum_header_size(Object *o) {
+
+        static uint64_t table[] = {
+                [OBJECT_DATA] = sizeof(DataObject),
+                [OBJECT_FIELD] = sizeof(FieldObject),
+                [OBJECT_ENTRY] = sizeof(EntryObject),
+                [OBJECT_DATA_HASH_TABLE] = sizeof(HashTableObject),
+                [OBJECT_FIELD_HASH_TABLE] = sizeof(HashTableObject),
+                [OBJECT_ENTRY_ARRAY] = sizeof(EntryArrayObject),
+                [OBJECT_TAG] = sizeof(TagObject),
+        };
+
+        if (o->object.type >= ELEMENTSOF(table) || table[o->object.type] <= 0)
+                return sizeof(ObjectHeader);
+
+        return table[o->object.type];
+}
+
 int journal_file_move_to_object(JournalFile *f, int type, uint64_t offset, Object **ret) {
         int r;
         void *t;
         Object *o;
         uint64_t s;
+        unsigned context;
 
         assert(f);
         assert(ret);
-        assert(type < _OBJECT_TYPE_MAX);
 
-        r = journal_file_move_to(f, type >= 0 ? type : WINDOW_UNKNOWN, offset, sizeof(ObjectHeader), &t);
+        /* One context for each type, plus one catch-all for the rest */
+        context = type > 0 && type < _OBJECT_TYPE_MAX ? type : 0;
+
+        r = journal_file_move_to(f, context, offset, sizeof(ObjectHeader), &t);
         if (r < 0)
                 return r;
 
@@ -457,6 +378,12 @@ int journal_file_move_to_object(JournalFile *f, int type, uint64_t offset, Objec
         if (s < sizeof(ObjectHeader))
                 return -EBADMSG;
 
+        if (o->object.type <= OBJECT_UNUSED)
+                return -EBADMSG;
+
+        if (s < minimum_header_size(o))
+                return -EBADMSG;
+
         if (type >= 0 && o->object.type != type)
                 return -EBADMSG;
 
@@ -508,6 +435,7 @@ static int journal_file_append_object(JournalFile *f, int type, uint64_t size, O
         void *t;
 
         assert(f);
+        assert(type > 0 && type < _OBJECT_TYPE_MAX);
         assert(size >= sizeof(ObjectHeader));
         assert(offset);
         assert(ret);
@@ -613,7 +541,7 @@ static int journal_file_map_data_hash_table(JournalFile *f) {
         s = le64toh(f->header->data_hash_table_size);
 
         r = journal_file_move_to(f,
-                                 WINDOW_DATA_HASH_TABLE,
+                                 OBJECT_DATA_HASH_TABLE,
                                  p, s,
                                  &t);
         if (r < 0)
@@ -634,7 +562,7 @@ static int journal_file_map_field_hash_table(JournalFile *f) {
         s = le64toh(f->header->field_hash_table_size);
 
         r = journal_file_move_to(f,
-                                 WINDOW_FIELD_HASH_TABLE,
+                                 OBJECT_FIELD_HASH_TABLE,
                                  p, s,
                                  &t);
         if (r < 0)
@@ -2428,6 +2356,7 @@ int journal_file_open(
                 bool compress,
                 bool authenticate,
                 JournalMetrics *metrics,
+                MMapCache *mmap_cache,
                 JournalFile *template,
                 JournalFile **ret) {
 
@@ -2457,6 +2386,19 @@ int journal_file_open(
         f->compress = compress;
         f->authenticate = authenticate;
 
+        if (mmap_cache)
+                f->mmap = mmap_cache_ref(mmap_cache);
+        else {
+                /* One context for each type, plus the zeroth catchall
+                 * context. One fd for the file plus one for each type
+                 * (which we need during verification */
+                f->mmap = mmap_cache_new(_OBJECT_TYPE_MAX, 1 + _OBJECT_TYPE_MAX);
+                if (!f->mmap) {
+                        r = -ENOMEM;
+                        goto fail;
+                }
+        }
+
         f->path = strdup(fname);
         if (!f->path) {
                 r = -ENOMEM;
@@ -2605,7 +2547,7 @@ int journal_file_rotate(JournalFile **f, bool compress, bool authenticate) {
 
         old_file->header->state = STATE_ARCHIVED;
 
-        r = journal_file_open(old_file->path, old_file->flags, old_file->mode, compress, authenticate, NULL, old_file, &new_file);
+        r = journal_file_open(old_file->path, old_file->flags, old_file->mode, compress, authenticate, NULL, old_file->mmap, old_file, &new_file);
         journal_file_close(old_file);
 
         *f = new_file;
@@ -2619,6 +2561,7 @@ int journal_file_open_reliably(
                 bool compress,
                 bool authenticate,
                 JournalMetrics *metrics,
+                MMapCache *mmap,
                 JournalFile *template,
                 JournalFile **ret) {
 
@@ -2626,7 +2569,7 @@ int journal_file_open_reliably(
         size_t l;
         char *p;
 
-        r = journal_file_open(fname, flags, mode, compress, authenticate, metrics, template, ret);
+        r = journal_file_open(fname, flags, mode, compress, authenticate, metrics, mmap, template, ret);
         if (r != -EBADMSG && /* corrupted */
             r != -ENODATA && /* truncated */
             r != -EHOSTDOWN && /* other machine */
@@ -2660,7 +2603,7 @@ int journal_file_open_reliably(
 
         log_warning("File %s corrupted or uncleanly shut down, renaming and replacing.", fname);
 
-        return journal_file_open(fname, flags, mode, compress, authenticate, metrics, template, ret);
+        return journal_file_open(fname, flags, mode, compress, authenticate, metrics, mmap, template, ret);
 }
 
 struct vacuum_info {
diff --git a/src/journal/journal-file.h b/src/journal/journal-file.h
index a16c8ffc3e..11a1c7d641 100644
--- a/src/journal/journal-file.h
+++ b/src/journal/journal-file.h
@@ -32,24 +32,7 @@
 #include "sparse-endian.h"
 #include "journal-def.h"
 #include "util.h"
-
-typedef struct Window {
-        void *ptr;
-        uint64_t offset;
-        uint64_t size;
-} Window;
-
-enum {
-        WINDOW_UNKNOWN = OBJECT_UNUSED,
-        WINDOW_DATA = OBJECT_DATA,
-        WINDOW_ENTRY = OBJECT_ENTRY,
-        WINDOW_DATA_HASH_TABLE = OBJECT_DATA_HASH_TABLE,
-        WINDOW_FIELD_HASH_TABLE = OBJECT_FIELD_HASH_TABLE,
-        WINDOW_ENTRY_ARRAY = OBJECT_ENTRY_ARRAY,
-        WINDOW_TAG = OBJECT_TAG,
-        WINDOW_HEADER,
-        _WINDOW_MAX
-};
+#include "mmap-cache.h"
 
 typedef struct JournalMetrics {
         uint64_t max_use;
@@ -76,11 +59,10 @@ typedef struct JournalFile {
         HashItem *data_hash_table;
         HashItem *field_hash_table;
 
-        Window windows[_WINDOW_MAX];
-
         uint64_t current_offset;
 
         JournalMetrics metrics;
+        MMapCache *mmap;
 
 #ifdef HAVE_XZ
         void *compress_buffer;
@@ -108,6 +90,7 @@ int journal_file_open(
                 bool compress,
                 bool authenticate,
                 JournalMetrics *metrics,
+                MMapCache *mmap,
                 JournalFile *template,
                 JournalFile **ret);
 
@@ -120,6 +103,7 @@ int journal_file_open_reliably(
                 bool compress,
                 bool authenticate,
                 JournalMetrics *metrics,
+                MMapCache *mmap,
                 JournalFile *template,
                 JournalFile **ret);
 
diff --git a/src/journal/journal-internal.h b/src/journal/journal-internal.h
index d17fdb2e92..86519be3d4 100644
--- a/src/journal/journal-internal.h
+++ b/src/journal/journal-internal.h
@@ -92,6 +92,7 @@ struct sd_journal {
         char *path;
 
         Hashmap *files;
+        MMapCache *mmap;
 
         Location current_location;
 
@@ -110,4 +111,3 @@ struct sd_journal {
 
 char *journal_make_match_string(sd_journal *j);
 void journal_print_header(sd_journal *j);
-
diff --git a/src/journal/journald.c b/src/journal/journald.c
index 8c41d9bab1..145663bf5b 100644
--- a/src/journal/journald.c
+++ b/src/journal/journald.c
@@ -315,7 +315,7 @@ static JournalFile* find_journal(Server *s, uid_t uid) {
                 journal_file_close(f);
         }
 
-        r = journal_file_open_reliably(p, O_RDWR|O_CREAT, 0640, s->compress, false, &s->system_metrics, s->system_journal, &f);
+        r = journal_file_open_reliably(p, O_RDWR|O_CREAT, 0640, s->compress, false, &s->system_metrics, s->mmap, s->system_journal, &f);
         free(p);
 
         if (r < 0)
@@ -2006,7 +2006,7 @@ static int system_journal_open(Server *s) {
                 if (!fn)
                         return -ENOMEM;
 
-                r = journal_file_open_reliably(fn, O_RDWR|O_CREAT, 0640, s->compress, true, &s->system_metrics, NULL, &s->system_journal);
+                r = journal_file_open_reliably(fn, O_RDWR|O_CREAT, 0640, s->compress, true, &s->system_metrics, s->mmap, NULL, &s->system_journal);
                 free(fn);
 
                 if (r >= 0)
@@ -2033,7 +2033,7 @@ static int system_journal_open(Server *s) {
                          * if it already exists, so that we can flush
                          * it into the system journal */
 
-                        r = journal_file_open(fn, O_RDWR, 0640, s->compress, false, &s->runtime_metrics, NULL, &s->runtime_journal);
+                        r = journal_file_open(fn, O_RDWR, 0640, s->compress, false, &s->runtime_metrics, s->mmap, NULL, &s->runtime_journal);
                         free(fn);
 
                         if (r < 0) {
@@ -2049,7 +2049,7 @@ static int system_journal_open(Server *s) {
                          * it if necessary. */
 
                         (void) mkdir_parents(fn, 0755);
-                        r = journal_file_open_reliably(fn, O_RDWR|O_CREAT, 0640, s->compress, false, &s->runtime_metrics, NULL, &s->runtime_journal);
+                        r = journal_file_open_reliably(fn, O_RDWR|O_CREAT, 0640, s->compress, false, &s->runtime_metrics, s->mmap, NULL, &s->runtime_journal);
                         free(fn);
 
                         if (r < 0) {
@@ -2793,6 +2793,10 @@ static int server_init(Server *s) {
         if (!s->user_journals)
                 return log_oom();
 
+        s->mmap = mmap_cache_new(_OBJECT_TYPE_MAX, USER_JOURNALS_MAX + 2);
+        if (!s->mmap)
+                return log_oom();
+
         s->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
         if (s->epoll_fd < 0) {
                 log_error("Failed to create epoll object: %m");
@@ -2919,6 +2923,9 @@ static void server_done(Server *s) {
 
         free(s->buffer);
         free(s->tty_path);
+
+        if (s->mmap)
+                mmap_cache_unref(s->mmap);
 }
 
 int main(int argc, char *argv[]) {
diff --git a/src/journal/journald.h b/src/journal/journald.h
index d08a194780..0202893d86 100644
--- a/src/journal/journald.h
+++ b/src/journal/journald.h
@@ -93,6 +93,8 @@ typedef struct Server {
 
         Storage storage;
 
+        MMapCache *mmap;
+
         bool dev_kmsg_readable;
 
         uint64_t *kernel_seqnum;
diff --git a/src/journal/mmap-cache.c b/src/journal/mmap-cache.c
new file mode 100644
index 0000000000..68dbe7015b
--- /dev/null
+++ b/src/journal/mmap-cache.c
@@ -0,0 +1,577 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2012 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <assert.h>
+#include <sys/mman.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "util.h"
+
+#include "mmap-cache.h"
+
+#define WINDOW_SIZE (8ULL*1024ULL*1024ULL)
+#define WINDOWS_MAX 32
+
+typedef struct Window {
+        int fd;
+        void *ptr;
+        uint64_t offset;
+        uint64_t size;
+
+        unsigned n_ref;
+        unsigned lru_prev;
+        unsigned lru_next;
+
+        unsigned by_fd_prev;
+        unsigned by_fd_next;
+} Window;
+
+typedef struct FileDescriptor {
+        int fd;
+        unsigned windows;
+} FileDescriptor;
+
+struct MMapCache {
+        unsigned n_ref;
+
+        unsigned contexts_max;
+        unsigned windows_max;
+        unsigned fds_max;
+
+        unsigned n_windows;
+        unsigned n_fds;
+
+        unsigned lru_first, lru_last;
+
+        Window *windows;
+        unsigned *by_context;
+        FileDescriptor *by_fd;
+};
+
+static void mmap_cache_window_unmap(MMapCache *m, unsigned w) {
+        Window *v;
+
+        assert(m);
+        assert(w < m->n_windows);
+
+        v = m->windows + w;
+        if (!v->ptr)
+                return;
+
+        munmap(v->ptr, v->size);
+        v->ptr = NULL;
+}
+
+static void mmap_cache_window_add_lru(MMapCache *m, unsigned w) {
+        Window *v;
+
+        assert(m);
+        assert(w < m->n_windows);
+
+        v = m->windows + w;
+        v->lru_prev = m->lru_last;
+        v->lru_next = (unsigned) -1;
+
+        m->lru_last = w;
+        if (m->lru_first == (unsigned) -1)
+                m->lru_first = w;
+}
+
+static void mmap_cache_window_remove_lru(MMapCache *m, unsigned w) {
+        Window *v;
+
+        assert(m);
+        assert(w < m->n_windows);
+
+        v = m->windows + w;
+
+        if (v->lru_prev == (unsigned) -1)
+                m->lru_first = v->lru_next;
+        else
+                m->windows[v->lru_prev].lru_next = v->lru_next;
+
+        if (v->lru_next == (unsigned) -1)
+                m->lru_last = v->lru_prev;
+        else
+                m->windows[v->lru_next].lru_prev = v->lru_prev;
+}
+
+static void mmap_cache_fd_add(MMapCache *m, unsigned fd_index, unsigned w) {
+        Window *v;
+
+        assert(m);
+        assert(fd_index < m->n_fds);
+
+        v = m->windows + w;
+        v->by_fd_next = m->by_fd[fd_index].windows;
+        v->by_fd_prev = (unsigned) -1;
+
+        m->by_fd[fd_index].windows = w;
+}
+
+static void mmap_cache_fd_remove(MMapCache *m, unsigned fd_index, unsigned w) {
+        Window *v;
+
+        assert(m);
+        assert(fd_index < m->n_fds);
+
+        v = m->windows + w;
+        if (v->by_fd_prev == (unsigned) -1)
+                m->by_fd[fd_index].windows = v->by_fd_next;
+        else
+                m->windows[v->by_fd_prev].by_fd_next = v->by_fd_next;
+
+        if (v->by_fd_next != (unsigned) -1)
+                m->windows[v->by_fd_next].by_fd_prev = v->by_fd_prev;
+}
+
+static void mmap_cache_context_unset(MMapCache *m, unsigned c) {
+        Window *v;
+        unsigned w;
+
+        assert(m);
+        assert(c < m->contexts_max);
+
+        if (m->by_context[c] == (unsigned) -1)
+                return;
+
+        w = m->by_context[c];
+        m->by_context[c] = (unsigned) -1;
+
+        v = m->windows + w;
+        assert(v->n_ref > 0);
+        v->n_ref --;
+
+        if (v->n_ref == 0)
+                mmap_cache_window_add_lru(m, w);
+}
+
+static void mmap_cache_context_set(MMapCache *m, unsigned c, unsigned w) {
+        Window *v;
+
+        assert(m);
+        assert(c < m->contexts_max);
+        assert(w < m->n_windows);
+
+        if (m->by_context[c] == w)
+                return;
+
+        mmap_cache_context_unset(m, c);
+
+        m->by_context[c] = w;
+
+        v = m->windows + w;
+        v->n_ref ++;
+        if (v->n_ref == 1)
+                mmap_cache_window_remove_lru(m, w);
+}
+
+static void mmap_cache_free(MMapCache *m) {
+
+        assert(m);
+
+        if (m->windows) {
+                unsigned w;
+
+                for (w = 0; w < m->n_windows; w++)
+                        mmap_cache_window_unmap(m, w);
+
+                free(m->windows);
+        }
+
+        free(m->by_context);
+        free(m->by_fd);
+        free(m);
+}
+
+MMapCache* mmap_cache_new(unsigned contexts_max, unsigned fds_max) {
+        MMapCache *m;
+
+        assert(contexts_max > 0);
+        assert(fds_max > 0);
+
+        m = new0(MMapCache, 1);
+        if (!m)
+                return NULL;
+
+        m->contexts_max = contexts_max;
+        m->fds_max = fds_max;
+        m->windows_max = MAX(m->contexts_max, WINDOWS_MAX);
+        m->n_ref = 1;
+        m->lru_first = (unsigned) -1;
+        m->lru_last = (unsigned) -1;
+
+        m->windows = new(Window, m->windows_max);
+        if (!m->windows) {
+                mmap_cache_free(m);
+                return NULL;
+        }
+
+        m->by_context = new(unsigned, m->contexts_max);
+        if (!m->by_context) {
+                mmap_cache_free(m);
+                return NULL;
+        }
+
+        memset(m->by_context, -1, m->contexts_max * sizeof(unsigned));
+
+        m->by_fd = new(FileDescriptor, m->fds_max);
+        if (!m->by_fd) {
+                mmap_cache_free(m);
+                return NULL;
+        }
+
+        return m;
+}
+
+MMapCache* mmap_cache_ref(MMapCache *m) {
+        assert(m);
+        assert(m->n_ref > 0);
+
+        m->n_ref++;
+        return m;
+}
+
+MMapCache* mmap_cache_unref(MMapCache *m) {
+        assert(m);
+        assert(m->n_ref > 0);
+
+        if (m->n_ref == 1)
+                mmap_cache_free(m);
+        else
+                m->n_ref--;
+
+        return NULL;
+}
+
+static int mmap_cache_allocate_window(MMapCache *m, unsigned *w) {
+        assert(m);
+        assert(w);
+
+        if (m->n_windows < m->windows_max) {
+                *w = m->n_windows ++;
+                return 0;
+        }
+
+        if (m->lru_first == (unsigned) -1)
+                return -E2BIG;
+
+        *w = m->lru_first;
+        mmap_cache_window_unmap(m, *w);
+        mmap_cache_window_remove_lru(m, *w);
+
+        return 0;
+}
+
+static int mmap_cache_make_room(MMapCache *m) {
+        unsigned w;
+
+        assert(m);
+
+        w = m->lru_first;
+        while (w != (unsigned) -1) {
+                Window *v;
+
+                v = m->windows + w;
+
+                if (v->ptr) {
+                        mmap_cache_window_unmap(m, w);
+                        return 1;
+                }
+
+                w = v->lru_next;
+        }
+
+        return 0;
+}
+
+static int mmap_cache_put(
+                MMapCache *m,
+                int fd,
+                unsigned fd_index,
+                int prot,
+                unsigned context,
+                uint64_t offset,
+                uint64_t size,
+                void **ret) {
+
+        unsigned w;
+        Window *v;
+        void *d;
+        uint64_t woffset, wsize;
+        int r;
+
+        assert(m);
+        assert(fd >= 0);
+        assert(context < m->contexts_max);
+        assert(size > 0);
+        assert(ret);
+
+        woffset = offset & ~((uint64_t) page_size() - 1ULL);
+        wsize = size + (offset - woffset);
+        wsize = PAGE_ALIGN(wsize);
+
+        if (wsize < WINDOW_SIZE) {
+                uint64_t delta;
+
+                delta = (WINDOW_SIZE - wsize) / 2;
+
+                if (delta > offset)
+                        woffset = 0;
+                else
+                        woffset -= delta;
+
+                wsize = WINDOW_SIZE;
+        }
+
+        for (;;) {
+                d = mmap(NULL, wsize, prot, MAP_SHARED, fd, woffset);
+                if (d != MAP_FAILED)
+                        break;
+                if (errno != ENOMEM)
+                        return -errno;
+
+                r = mmap_cache_make_room(m);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        return -ENOMEM;
+        }
+
+        r = mmap_cache_allocate_window(m, &w);
+        if (r < 0) {
+                munmap(d, wsize);
+                return r;
+        }
+
+        v = m->windows + w;
+        v->fd = fd;
+        v->ptr = d;
+        v->offset = woffset;
+        v->size = wsize;
+
+        v->n_ref = 0;
+        v->lru_prev = v->lru_next = (unsigned) -1;
+
+        mmap_cache_fd_add(m, fd_index, w);
+        mmap_cache_context_set(m, context, w);
+
+        *ret = (uint8_t*) d + (offset - woffset);
+        return 1;
+}
+
+static int fd_cmp(const void *_a, const void *_b) {
+        const FileDescriptor *a = _a, *b = _b;
+
+        if (a->fd < b->fd)
+                return -1;
+        if (a->fd > b->fd)
+                return 1;
+
+        return 0;
+}
+
+static int mmap_cache_get_fd_index(MMapCache *m, int fd, unsigned *fd_index) {
+        FileDescriptor *j;
+
+        assert(m);
+        assert(fd >= 0);
+        assert(fd_index);
+
+        j = bsearch(&fd, m->by_fd, m->n_fds, sizeof(m->by_fd[0]), fd_cmp);
+        if (!j) {
+                if (m->n_fds >= m->fds_max)
+                        return -E2BIG;
+
+                j = m->by_fd + m->n_fds ++;
+                j->fd = fd;
+                j->windows = (unsigned) -1;
+
+                qsort(m->by_fd, m->n_fds, sizeof(m->by_fd[0]), fd_cmp);
+                j = bsearch(&fd, m->by_fd, m->n_fds, sizeof(m->by_fd[0]), fd_cmp);
+        }
+
+        *fd_index = (unsigned) (j - m->by_fd);
+        return 0;
+}
+
+static bool mmap_cache_test_window(
+                MMapCache *m,
+                unsigned w,
+                uint64_t offset,
+                uint64_t size) {
+        Window *v;
+
+        assert(m);
+        assert(w < m->n_windows);
+        assert(size > 0);
+
+        v = m->windows + w;
+
+        return offset >= v->offset &&
+                offset + size <= v->offset + v->size;
+}
+
+static int mmap_cache_current(
+                MMapCache *m,
+                int fd,
+                unsigned context,
+                uint64_t offset,
+                uint64_t size,
+                void **ret) {
+
+        Window *v;
+        unsigned w;
+
+        assert(m);
+        assert(fd >= 0);
+        assert(context < m->contexts_max);
+        assert(size > 0);
+        assert(ret);
+
+        if (m->by_context[context] == (unsigned) -1)
+                return 0;
+
+        w = m->by_context[context];
+        v = m->windows + w;
+
+        if (v->fd != fd)
+                return 0;
+
+        if (!mmap_cache_test_window(m, w, offset, size))
+                return 0;
+
+        *ret = (uint8_t*) v->ptr + (offset - v->offset);
+        return 1;
+}
+
+static int mmap_cache_find(
+                MMapCache *m,
+                unsigned fd_index,
+                unsigned context,
+                uint64_t offset,
+                uint64_t size,
+                void **ret) {
+
+        Window *v = NULL;
+        unsigned w;
+
+        assert(m);
+        assert(fd_index < m->n_fds);
+        assert(context < m->contexts_max);
+        assert(size > 0);
+        assert(ret);
+
+        w = m->by_fd[fd_index].windows;
+        while (w != (unsigned) -1) {
+                if (mmap_cache_test_window(m, w, offset, size))
+                        break;
+
+                w = m->windows[w].by_fd_next;
+        }
+
+        if (w == (unsigned) -1)
+                return 0;
+
+        mmap_cache_context_set(m, context, w);
+
+        v = m->windows + w;
+        *ret = (uint8_t*) v->ptr + (offset - v->offset);
+        return 1;
+}
+
+int mmap_cache_get(
+                MMapCache *m,
+                int fd,
+                int prot,
+                unsigned context,
+                uint64_t offset,
+                uint64_t size,
+                void **ret) {
+
+        unsigned fd_index;
+        int r;
+
+        assert(m);
+        assert(fd >= 0);
+        assert(context < m->contexts_max);
+        assert(size > 0);
+        assert(ret);
+
+        /* Maybe the current pointer for this context is already the
+         * right one? */
+        r = mmap_cache_current(m, fd, context, offset, size, ret);
+        if (r != 0)
+                return r;
+
+        /* OK, let's find the chain for this FD */
+        r = mmap_cache_get_fd_index(m, fd, &fd_index);
+        if (r < 0)
+                return r;
+
+        /* And let's look through the available mmaps */
+        r = mmap_cache_find(m, fd_index, context, offset, size, ret);
+        if (r != 0)
+                return r;
+
+        /* Not found? Then, let's add it */
+        return mmap_cache_put(m, fd, fd_index, prot, context, offset, size, ret);
+}
+
+void mmap_cache_close_fd(MMapCache *m, int fd) {
+        FileDescriptor *j;
+        unsigned fd_index, c, w;
+
+        assert(m);
+        assert(fd > 0);
+
+        j = bsearch(&fd, m->by_fd, m->n_fds, sizeof(m->by_fd[0]), fd_cmp);
+        if (!j)
+                return;
+        fd_index = (unsigned) (j - m->by_fd);
+
+        for (c = 0; c < m->contexts_max; c++) {
+                w = m->by_context[c];
+                if (w == (unsigned) -1)
+                        continue;
+
+                if (m->windows[w].fd == fd)
+                        mmap_cache_context_unset(m, c);
+        }
+
+        w = m->by_fd[fd_index].windows;
+        while (w != (unsigned) -1) {
+
+                mmap_cache_fd_remove(m, fd_index, w);
+                mmap_cache_window_unmap(m, w);
+
+                w = m->by_fd[fd_index].windows;
+        }
+
+        memmove(m->by_fd + fd_index, m->by_fd + fd_index + 1, (m->n_fds - (fd_index + 1)) * sizeof(FileDescriptor));
+        m->n_fds --;
+}
+
+void mmap_cache_close_context(MMapCache *m, unsigned context) {
+        mmap_cache_context_unset(m, context);
+}
diff --git a/src/journal/mmap-cache.h b/src/journal/mmap-cache.h
new file mode 100644
index 0000000000..0a88fc584f
--- /dev/null
+++ b/src/journal/mmap-cache.h
@@ -0,0 +1,34 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+#pragma once
+
+/***
+  This file is part of systemd.
+
+  Copyright 2012 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <inttypes.h>
+
+typedef struct MMapCache MMapCache;
+
+MMapCache* mmap_cache_new(unsigned contexts_max, unsigned fds_max);
+MMapCache* mmap_cache_ref(MMapCache *m);
+MMapCache* mmap_cache_unref(MMapCache *m);
+
+int mmap_cache_get(MMapCache *m, int fd, int prot, unsigned context, uint64_t offset, uint64_t size, void **ret);
+void mmap_cache_close_fd(MMapCache *m, int fd);
+void mmap_cache_close_context(MMapCache *m, unsigned context);
diff --git a/src/journal/sd-journal.c b/src/journal/sd-journal.c
index 359a7cac3e..41526b35bf 100644
--- a/src/journal/sd-journal.c
+++ b/src/journal/sd-journal.c
@@ -1118,7 +1118,7 @@ static int add_file(sd_journal *j, const char *prefix, const char *filename) {
                 return 0;
         }
 
-        r = journal_file_open(path, O_RDONLY, 0, false, false, NULL, NULL, &f);
+        r = journal_file_open(path, O_RDONLY, 0, false, false, NULL, j->mmap, NULL, &f);
         free(path);
 
         if (r < 0) {
@@ -1439,6 +1439,17 @@ static sd_journal *journal_new(int flags, const char *path) {
                 return NULL;
         }
 
+        /* One context for each type, plus the zeroth catchall
+         * context. One fd for each file plus one for each type, which
+         * is need when verifying things */
+        j->mmap = mmap_cache_new(_OBJECT_TYPE_MAX, JOURNAL_FILES_MAX + _OBJECT_TYPE_MAX);
+        if (!j->mmap) {
+                hashmap_free(j->files);
+                hashmap_free(j->directories_by_path);
+                free(j->path);
+                free(j);
+        }
+
         return j;
 }
 
@@ -1527,6 +1538,9 @@ _public_ void sd_journal_close(sd_journal *j) {
 
         sd_journal_flush_matches(j);
 
+        if (j->mmap)
+                mmap_cache_unref(j->mmap);
+
         free(j->path);
         free(j);
 }
diff --git a/src/journal/test-journal-stream.c b/src/journal/test-journal-stream.c
index 0925995fca..707dcc178b 100644
--- a/src/journal/test-journal-stream.c
+++ b/src/journal/test-journal-stream.c
@@ -79,9 +79,9 @@ int main(int argc, char *argv[]) {
         assert_se(mkdtemp(t));
         assert_se(chdir(t) >= 0);
 
-        assert_se(journal_file_open("one.journal", O_RDWR|O_CREAT, 0666, true, false, NULL, NULL, &one) == 0);
-        assert_se(journal_file_open("two.journal", O_RDWR|O_CREAT, 0666, true, false, NULL, NULL, &two) == 0);
-        assert_se(journal_file_open("three.journal", O_RDWR|O_CREAT, 0666, true, false, NULL, NULL, &three) == 0);
+        assert_se(journal_file_open("one.journal", O_RDWR|O_CREAT, 0666, true, false, NULL, NULL, NULL, &one) == 0);
+        assert_se(journal_file_open("two.journal", O_RDWR|O_CREAT, 0666, true, false, NULL, NULL, NULL, &two) == 0);
+        assert_se(journal_file_open("three.journal", O_RDWR|O_CREAT, 0666, true, false, NULL, NULL, NULL, &three) == 0);
 
         for (i = 0; i < N_ENTRIES; i++) {
                 char *p, *q;
diff --git a/src/journal/test-journal.c b/src/journal/test-journal.c
index 8f01b4d82e..2fd19a755b 100644
--- a/src/journal/test-journal.c
+++ b/src/journal/test-journal.c
@@ -41,7 +41,7 @@ int main(int argc, char *argv[]) {
         assert_se(mkdtemp(t));
         assert_se(chdir(t) >= 0);
 
-        assert_se(journal_file_open("test.journal", O_RDWR|O_CREAT, 0666, true, false, NULL, NULL, &f) == 0);
+        assert_se(journal_file_open("test.journal", O_RDWR|O_CREAT, 0666, true, true, NULL, NULL, NULL, &f) == 0);
 
         dual_timestamp_get(&ts);