Merge branch 'master' of /pub/scm/linux/kernel/git/torvalds/linux-2.6

2 files changed, 90 insertions, 117 deletions

diff --git a/mm/slub.c b/mm/slub.c
index 74c65af0a54f..0863fd38a5ce 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -291,32 +291,16 @@ static inline struct kmem_cache_cpu *get_cpu_slab(struct kmem_cache *s, int cpu)
 #endif
 }
 
-/*
- * The end pointer in a slab is special. It points to the first object in the
- * slab but has bit 0 set to mark it.
- *
- * Note that SLUB relies on page_mapping returning NULL for pages with bit 0
- * in the mapping set.
- */
-static inline int is_end(void *addr)
-{
-        return (unsigned long)addr & PAGE_MAPPING_ANON;
-}
-
-static void *slab_address(struct page *page)
-{
-        return page->end - PAGE_MAPPING_ANON;
-}
-
+/* Verify that a pointer has an address that is valid within a slab page */
 static inline int check_valid_pointer(struct kmem_cache *s,
                                 struct page *page, const void *object)
 {
         void *base;
 
-        if (object == page->end)
+        if (!object)
                 return 1;
 
-        base = slab_address(page);
+        base = page_address(page);
         if (object < base || object >= base + s->objects * s->size ||
                 (object - base) % s->size) {
                 return 0;
@@ -349,8 +333,7 @@ static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp)
 
 /* Scan freelist */
 #define for_each_free_object(__p, __s, __free) \
-        for (__p = (__free); (__p) != page->end; __p = get_freepointer((__s),\
-                __p))
+        for (__p = (__free); __p; __p = get_freepointer((__s), __p))
 
 /* Determine object index from a given position */
 static inline int slab_index(void *p, struct kmem_cache *s, void *addr)
@@ -502,7 +485,7 @@ static void slab_fix(struct kmem_cache *s, char *fmt, ...)
 static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)
 {
         unsigned int off;       /* Offset of last byte */
-        u8 *addr = slab_address(page);
+        u8 *addr = page_address(page);
 
         print_tracking(s, p);
 
@@ -637,7 +620,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page,
  *      A. Free pointer (if we cannot overwrite object on free)
  *      B. Tracking data for SLAB_STORE_USER
  *      C. Padding to reach required alignment boundary or at mininum
- *              one word if debuggin is on to be able to detect writes
+ *              one word if debugging is on to be able to detect writes
  *              before the word boundary.
  *
  *      Padding is done using 0x5a (POISON_INUSE)
@@ -680,7 +663,7 @@ static int slab_pad_check(struct kmem_cache *s, struct page *page)
         if (!(s->flags & SLAB_POISON))
                 return 1;
 
-        start = slab_address(page);
+        start = page_address(page);
         end = start + (PAGE_SIZE << s->order);
         length = s->objects * s->size;
         remainder = end - (start + length);
@@ -748,7 +731,7 @@ static int check_object(struct kmem_cache *s, struct page *page,
                  * of the free objects in this slab. May cause
                  * another error because the object count is now wrong.
                  */
-                set_freepointer(s, p, page->end);
+                set_freepointer(s, p, NULL);
                 return 0;
         }
         return 1;
@@ -782,18 +765,18 @@ static int on_freelist(struct kmem_cache *s, struct page *page, void *search)
         void *fp = page->freelist;
         void *object = NULL;
 
-        while (fp != page->end && nr <= s->objects) {
+        while (fp && nr <= s->objects) {
                 if (fp == search)
                         return 1;
                 if (!check_valid_pointer(s, page, fp)) {
                         if (object) {
                                 object_err(s, page, object,
                                         "Freechain corrupt");
-                                set_freepointer(s, object, page->end);
+                                set_freepointer(s, object, NULL);
                                 break;
                         } else {
                                 slab_err(s, page, "Freepointer corrupt");
-                                page->freelist = page->end;
+                                page->freelist = NULL;
                                 page->inuse = s->objects;
                                 slab_fix(s, "Freelist cleared");
                                 return 0;
@@ -870,7 +853,7 @@ static int alloc_debug_processing(struct kmem_cache *s, struct page *page,
         if (!check_slab(s, page))
                 goto bad;
 
-        if (object && !on_freelist(s, page, object)) {
+        if (!on_freelist(s, page, object)) {
                 object_err(s, page, object, "Object already allocated");
                 goto bad;
         }
@@ -880,7 +863,7 @@ static int alloc_debug_processing(struct kmem_cache *s, struct page *page,
                 goto bad;
         }
 
-        if (object && !check_object(s, page, object, 0))
+        if (!check_object(s, page, object, 0))
                 goto bad;
 
         /* Success perform special debug activities for allocs */
@@ -899,7 +882,7 @@ bad:
                  */
                 slab_fix(s, "Marking all objects used");
                 page->inuse = s->objects;
-                page->freelist = page->end;
+                page->freelist = NULL;
         }
         return 0;
 }
@@ -939,7 +922,7 @@ static int free_debug_processing(struct kmem_cache *s, struct page *page,
         }
 
         /* Special debug activities for freeing objects */
-        if (!SlabFrozen(page) && page->freelist == page->end)
+        if (!SlabFrozen(page) && !page->freelist)
                 remove_full(s, page);
         if (s->flags & SLAB_STORE_USER)
                 set_track(s, object, TRACK_FREE, addr);
@@ -1015,30 +998,11 @@ static unsigned long kmem_cache_flags(unsigned long objsize,
         void (*ctor)(struct kmem_cache *, void *))
 {
         /*
-         * The page->offset field is only 16 bit wide. This is an offset
-         * in units of words from the beginning of an object. If the slab
-         * size is bigger then we cannot move the free pointer behind the
-         * object anymore.
-         *
-         * On 32 bit platforms the limit is 256k. On 64bit platforms
-         * the limit is 512k.
-         *
-         * Debugging or ctor may create a need to move the free
-         * pointer. Fail if this happens.
+         * Enable debugging if selected on the kernel commandline.
          */
-        if (objsize >= 65535 * sizeof(void *)) {
-                BUG_ON(flags & (SLAB_RED_ZONE | SLAB_POISON |
-                                SLAB_STORE_USER | SLAB_DESTROY_BY_RCU));
-                BUG_ON(ctor);
-        } else {
-                /*
-                 * Enable debugging if selected on the kernel commandline.
-                 */
-                if (slub_debug && (!slub_debug_slabs ||
-                    strncmp(slub_debug_slabs, name,
-                        strlen(slub_debug_slabs)) == 0))
-                                flags |= slub_debug;
-        }
+        if (slub_debug && (!slub_debug_slabs ||
+            strncmp(slub_debug_slabs, name, strlen(slub_debug_slabs)) == 0))
+                        flags |= slub_debug;
 
         return flags;
 }
@@ -1124,7 +1088,6 @@ static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)
                 SetSlabDebug(page);
 
         start = page_address(page);
-        page->end = start + 1;
 
         if (unlikely(s->flags & SLAB_POISON))
                 memset(start, POISON_INUSE, PAGE_SIZE << s->order);
@@ -1136,7 +1099,7 @@ static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)
                 last = p;
         }
         setup_object(s, page, last);
-        set_freepointer(s, last, page->end);
+        set_freepointer(s, last, NULL);
 
         page->freelist = start;
         page->inuse = 0;
@@ -1152,7 +1115,7 @@ static void __free_slab(struct kmem_cache *s, struct page *page)
                 void *p;
 
                 slab_pad_check(s, page);
-                for_each_object(p, s, slab_address(page))
+                for_each_object(p, s, page_address(page))
                         check_object(s, page, p, 0);
                 ClearSlabDebug(page);
         }
@@ -1162,7 +1125,6 @@ static void __free_slab(struct kmem_cache *s, struct page *page)
                 NR_SLAB_RECLAIMABLE : NR_SLAB_UNRECLAIMABLE,
                 -pages);
 
-        page->mapping = NULL;
         __free_pages(page, s->order);
 }
 
@@ -1307,7 +1269,7 @@ static struct page *get_any_partial(struct kmem_cache *s, gfp_t flags)
          * may return off node objects because partial slabs are obtained
          * from other nodes and filled up.
          *
-         * If /sys/slab/xx/defrag_ratio is set to 100 (which makes
+         * If /sys/kernel/slab/xx/defrag_ratio is set to 100 (which makes
          * defrag_ratio = 1000) then every (well almost) allocation will
          * first attempt to defrag slab caches on other nodes. This means
          * scanning over all nodes to look for partial slabs which may be
@@ -1366,7 +1328,7 @@ static void unfreeze_slab(struct kmem_cache *s, struct page *page, int tail)
         ClearSlabFrozen(page);
         if (page->inuse) {
 
-                if (page->freelist != page->end) {
+                if (page->freelist) {
                         add_partial(n, page, tail);
                         stat(c, tail ? DEACTIVATE_TO_TAIL : DEACTIVATE_TO_HEAD);
                 } else {
@@ -1382,9 +1344,11 @@ static void unfreeze_slab(struct kmem_cache *s, struct page *page, int tail)
                          * Adding an empty slab to the partial slabs in order
                          * to avoid page allocator overhead. This slab needs
                          * to come after the other slabs with objects in
-                         * order to fill them up. That way the size of the
-                         * partial list stays small. kmem_cache_shrink can
-                         * reclaim empty slabs from the partial list.
+                         * so that the others get filled first. That way the
+                         * size of the partial list stays small.
+                         *
+                         * kmem_cache_shrink can reclaim any empty slabs from the
+                         * partial list.
                          */
                         add_partial(n, page, 1);
                         slab_unlock(page);
@@ -1407,15 +1371,11 @@ static void deactivate_slab(struct kmem_cache *s, struct kmem_cache_cpu *c)
         if (c->freelist)
                 stat(c, DEACTIVATE_REMOTE_FREES);
         /*
-         * Merge cpu freelist into freelist. Typically we get here
+         * Merge cpu freelist into slab freelist. Typically we get here
          * because both freelists are empty. So this is unlikely
          * to occur.
-         *
-         * We need to use _is_end here because deactivate slab may
-         * be called for a debug slab. Then c->freelist may contain
-         * a dummy pointer.
          */
-        while (unlikely(!is_end(c->freelist))) {
+        while (unlikely(c->freelist)) {
                 void **object;
 
                 tail = 0;       /* Hot objects. Put the slab first */
@@ -1442,6 +1402,7 @@ static inline void flush_slab(struct kmem_cache *s, struct kmem_cache_cpu *c)
 
 /*
  * Flush cpu slab.
+ *
  * Called from IPI handler with interrupts disabled.
  */
 static inline void __flush_cpu_slab(struct kmem_cache *s, int cpu)
@@ -1500,7 +1461,8 @@ static inline int node_match(struct kmem_cache_cpu *c, int node)
  * rest of the freelist to the lockless freelist.
  *
  * And if we were unable to get a new slab from the partial slab lists then
- * we need to allocate a new slab. This is slowest path since we may sleep.
+ * we need to allocate a new slab. This is the slowest path since it involves
+ * a call to the page allocator and the setup of a new slab.
  */
 static void *__slab_alloc(struct kmem_cache *s,
                 gfp_t gfpflags, int node, void *addr, struct kmem_cache_cpu *c)
@@ -1514,18 +1476,19 @@ static void *__slab_alloc(struct kmem_cache *s,
         slab_lock(c->page);
         if (unlikely(!node_match(c, node)))
                 goto another_slab;
+
         stat(c, ALLOC_REFILL);
+
 load_freelist:
         object = c->page->freelist;
-        if (unlikely(object == c->page->end))
+        if (unlikely(!object))
                 goto another_slab;
         if (unlikely(SlabDebug(c->page)))
                 goto debug;
 
-        object = c->page->freelist;
         c->freelist = object[c->offset];
         c->page->inuse = s->objects;
-        c->page->freelist = c->page->end;
+        c->page->freelist = NULL;
         c->node = page_to_nid(c->page);
 unlock_out:
         slab_unlock(c->page);
@@ -1578,7 +1541,6 @@ new_slab:
 
         return NULL;
 debug:
-        object = c->page->freelist;
         if (!alloc_debug_processing(s, c->page, object, addr))
                 goto another_slab;
 
@@ -1607,7 +1569,7 @@ static __always_inline void *slab_alloc(struct kmem_cache *s,
 
         local_irq_save(flags);
         c = get_cpu_slab(s, smp_processor_id());
-        if (unlikely(is_end(c->freelist) || !node_match(c, node)))
+        if (unlikely(!c->freelist || !node_match(c, node)))
 
                 object = __slab_alloc(s, gfpflags, node, addr, c);
 
@@ -1659,6 +1621,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
 
         if (unlikely(SlabDebug(page)))
                 goto debug;
+
 checks_ok:
         prior = object[offset] = page->freelist;
         page->freelist = object;
@@ -1673,11 +1636,10 @@ checks_ok:
                 goto slab_empty;
 
         /*
-         * Objects left in the slab. If it
-         * was not on the partial list before
+         * Objects left in the slab. If it was not on the partial list before
          * then add it.
          */
-        if (unlikely(prior == page->end)) {
+        if (unlikely(!prior)) {
                 add_partial(get_node(s, page_to_nid(page)), page, 1);
                 stat(c, FREE_ADD_PARTIAL);
         }
@@ -1687,7 +1649,7 @@ out_unlock:
         return;
 
 slab_empty:
-        if (prior != page->end) {
+        if (prior) {
                 /*
                  * Slab still on the partial list.
                  */
@@ -1724,8 +1686,8 @@ static __always_inline void slab_free(struct kmem_cache *s,
         unsigned long flags;
 
         local_irq_save(flags);
-        debug_check_no_locks_freed(object, s->objsize);
         c = get_cpu_slab(s, smp_processor_id());
+        debug_check_no_locks_freed(object, c->objsize);
         if (likely(page == c->page && c->node >= 0)) {
                 object[c->offset] = c->freelist;
                 c->freelist = object;
@@ -1888,13 +1850,11 @@ static unsigned long calculate_alignment(unsigned long flags,
                 unsigned long align, unsigned long size)
 {
         /*
-         * If the user wants hardware cache aligned objects then
-         * follow that suggestion if the object is sufficiently
-         * large.
+         * If the user wants hardware cache aligned objects then follow that
+         * suggestion if the object is sufficiently large.
          *
-         * The hardware cache alignment cannot override the
-         * specified alignment though. If that is greater
-         * then use it.
+         * The hardware cache alignment cannot override the specified
+         * alignment though. If that is greater then use it.
          */
         if ((flags & SLAB_HWCACHE_ALIGN) &&
                         size > cache_line_size() / 2)
@@ -1910,7 +1870,7 @@ static void init_kmem_cache_cpu(struct kmem_cache *s,
                         struct kmem_cache_cpu *c)
 {
         c->page = NULL;
-        c->freelist = (void *)PAGE_MAPPING_ANON;
+        c->freelist = NULL;
         c->node = 0;
         c->offset = s->offset / sizeof(void *);
         c->objsize = s->objsize;
@@ -2092,6 +2052,7 @@ static struct kmem_cache_node *early_kmem_cache_node_alloc(gfp_t gfpflags,
 #endif
         init_kmem_cache_node(n);
         atomic_long_inc(&n->nr_slabs);
+
         /*
          * lockdep requires consistent irq usage for each lock
          * so even though there cannot be a race this early in
@@ -2173,6 +2134,14 @@ static int calculate_sizes(struct kmem_cache *s)
         unsigned long align = s->align;
 
         /*
+         * Round up object size to the next word boundary. We can only
+         * place the free pointer at word boundaries and this determines
+         * the possible location of the free pointer.
+         */
+        size = ALIGN(size, sizeof(void *));
+
+#ifdef CONFIG_SLUB_DEBUG
+        /*
          * Determine if we can poison the object itself. If the user of
          * the slab may touch the object after free or before allocation
          * then we should never poison the object itself.
@@ -2183,14 +2152,7 @@ static int calculate_sizes(struct kmem_cache *s)
         else
                 s->flags &= ~__OBJECT_POISON;
 
-        /*
-         * Round up object size to the next word boundary. We can only
-         * place the free pointer at word boundaries and this determines
-         * the possible location of the free pointer.
-         */
-        size = ALIGN(size, sizeof(void *));
 
-#ifdef CONFIG_SLUB_DEBUG
         /*
          * If we are Redzoning then check if there is some space between the
          * end of the object and the free pointer. If not then add an
@@ -2343,7 +2305,7 @@ int kmem_ptr_validate(struct kmem_cache *s, const void *object)
         /*
          * We could also check if the object is on the slabs freelist.
          * But this would be too expensive and it seems that the main
-         * purpose of kmem_ptr_valid is to check if the object belongs
+         * purpose of kmem_ptr_valid() is to check if the object belongs
          * to a certain slab.
          */
         return 1;
@@ -2630,13 +2592,24 @@ void *__kmalloc(size_t size, gfp_t flags)
 }
 EXPORT_SYMBOL(__kmalloc);
 
+static void *kmalloc_large_node(size_t size, gfp_t flags, int node)
+{
+        struct page *page = alloc_pages_node(node, flags | __GFP_COMP,
+                                                get_order(size));
+
+        if (page)
+                return page_address(page);
+        else
+                return NULL;
+}
+
 #ifdef CONFIG_NUMA
 void *__kmalloc_node(size_t size, gfp_t flags, int node)
 {
         struct kmem_cache *s;
 
         if (unlikely(size > PAGE_SIZE))
-                return kmalloc_large(size, flags);
+                return kmalloc_large_node(size, flags, node);
 
         s = get_slab(size, flags);
 
@@ -2653,19 +2626,17 @@ size_t ksize(const void *object)
         struct page *page;
         struct kmem_cache *s;
 
-        BUG_ON(!object);
         if (unlikely(object == ZERO_SIZE_PTR))
                 return 0;
 
         page = virt_to_head_page(object);
-        BUG_ON(!page);
 
         if (unlikely(!PageSlab(page)))
                 return PAGE_SIZE << compound_order(page);
 
         s = page->slab;
-        BUG_ON(!s);
 
+#ifdef CONFIG_SLUB_DEBUG
         /*
          * Debugging requires use of the padding between object
          * and whatever may come after it.
@@ -2673,6 +2644,7 @@ size_t ksize(const void *object)
         if (s->flags & (SLAB_RED_ZONE | SLAB_POISON))
                 return s->objsize;
 
+#endif
         /*
          * If we have the need to store the freelist pointer
          * back there or track user information then we can
@@ -2680,7 +2652,6 @@ size_t ksize(const void *object)
          */
         if (s->flags & (SLAB_DESTROY_BY_RCU | SLAB_STORE_USER))
                 return s->inuse;
-
         /*
          * Else we can use all the padding etc for the allocation
          */
@@ -2957,7 +2928,7 @@ void __init kmem_cache_init(void)
         /*
          * Patch up the size_index table if we have strange large alignment
          * requirements for the kmalloc array. This is only the case for
-         * mips it seems. The standard arches will not generate any code here.
+         * MIPS it seems. The standard arches will not generate any code here.
          *
          * Largest permitted alignment is 256 bytes due to the way we
          * handle the index determination for the smaller caches.
@@ -2986,7 +2957,6 @@ void __init kmem_cache_init(void)
         kmem_size = sizeof(struct kmem_cache);
 #endif
 
-
         printk(KERN_INFO
                 "SLUB: Genslabs=%d, HWalign=%d, Order=%d-%d, MinObjects=%d,"
                 " CPUs=%d, Nodes=%d\n",
@@ -3083,12 +3053,15 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
                  */
                 for_each_online_cpu(cpu)
                         get_cpu_slab(s, cpu)->objsize = s->objsize;
+
                 s->inuse = max_t(int, s->inuse, ALIGN(size, sizeof(void *)));
                 up_write(&slub_lock);
+
                 if (sysfs_slab_alias(s, name))
                         goto err;
                 return s;
         }
+
         s = kmalloc(kmem_size, GFP_KERNEL);
         if (s) {
                 if (kmem_cache_open(s, GFP_KERNEL, name,
@@ -3184,7 +3157,7 @@ void *__kmalloc_node_track_caller(size_t size, gfp_t gfpflags,
         struct kmem_cache *s;
 
         if (unlikely(size > PAGE_SIZE))
-                return kmalloc_large(size, gfpflags);
+                return kmalloc_large_node(size, gfpflags, node);
 
         s = get_slab(size, gfpflags);
 
@@ -3199,7 +3172,7 @@ static int validate_slab(struct kmem_cache *s, struct page *page,
                                                 unsigned long *map)
 {
         void *p;
-        void *addr = slab_address(page);
+        void *addr = page_address(page);
 
         if (!check_slab(s, page) ||
                         !on_freelist(s, page, NULL))
@@ -3482,7 +3455,7 @@ static int add_location(struct loc_track *t, struct kmem_cache *s,
 static void process_slab(struct loc_track *t, struct kmem_cache *s,
                 struct page *page, enum track_item alloc)
 {
-        void *addr = slab_address(page);
+        void *addr = page_address(page);
         DECLARE_BITMAP(map, s->objects);
         void *p;
 
@@ -3591,8 +3564,8 @@ enum slab_stat_type {
 #define SO_CPU          (1 << SL_CPU)
 #define SO_OBJECTS      (1 << SL_OBJECTS)
 
-static unsigned long slab_objects(struct kmem_cache *s,
-                        char *buf, unsigned long flags)
+static ssize_t show_slab_objects(struct kmem_cache *s,
+                            char *buf, unsigned long flags)
 {
         unsigned long total = 0;
         int cpu;
@@ -3602,6 +3575,8 @@ static unsigned long slab_objects(struct kmem_cache *s,
         unsigned long *per_cpu;
 
         nodes = kzalloc(2 * sizeof(unsigned long) * nr_node_ids, GFP_KERNEL);
+        if (!nodes)
+                return -ENOMEM;
         per_cpu = nodes + nr_node_ids;
 
         for_each_possible_cpu(cpu) {
@@ -3754,25 +3729,25 @@ SLAB_ATTR_RO(aliases);
 
 static ssize_t slabs_show(struct kmem_cache *s, char *buf)
 {
-        return slab_objects(s, buf, SO_FULL|SO_PARTIAL|SO_CPU);
+        return show_slab_objects(s, buf, SO_FULL|SO_PARTIAL|SO_CPU);
 }
 SLAB_ATTR_RO(slabs);
 
 static ssize_t partial_show(struct kmem_cache *s, char *buf)
 {
-        return slab_objects(s, buf, SO_PARTIAL);
+        return show_slab_objects(s, buf, SO_PARTIAL);
 }
 SLAB_ATTR_RO(partial);
 
 static ssize_t cpu_slabs_show(struct kmem_cache *s, char *buf)
 {
-        return slab_objects(s, buf, SO_CPU);
+        return show_slab_objects(s, buf, SO_CPU);
 }
 SLAB_ATTR_RO(cpu_slabs);
 
 static ssize_t objects_show(struct kmem_cache *s, char *buf)
 {
-        return slab_objects(s, buf, SO_FULL|SO_PARTIAL|SO_CPU|SO_OBJECTS);
+        return show_slab_objects(s, buf, SO_FULL|SO_PARTIAL|SO_CPU|SO_OBJECTS);
 }
 SLAB_ATTR_RO(objects);
 
@@ -3971,7 +3946,6 @@ SLAB_ATTR(remote_node_defrag_ratio);
 #endif
 
 #ifdef CONFIG_SLUB_STATS
-
 static int show_stat(struct kmem_cache *s, char *buf, enum stat_item si)
 {
         unsigned long sum  = 0;
@@ -4155,8 +4129,8 @@ static struct kset *slab_kset;
 #define ID_STR_LENGTH 64
 
 /* Create a unique string id for a slab cache:
- * format
- * :[flags-]size:[memory address of kmemcache]
+ *
+ * Format       :[flags-]size
  */
 static char *create_unique_id(struct kmem_cache *s)
 {
diff --git a/mm/truncate.c b/mm/truncate.c
index c35c49e54fb6..7d20ce41ecf5 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -134,8 +134,7 @@ invalidate_complete_page(struct address_space *mapping, struct page *page)
 }
 
 /**
- * truncate_inode_pages - truncate range of pages specified by start and
- * end byte offsets
+ * truncate_inode_pages - truncate range of pages specified by start & end byte offsets
  * @mapping: mapping to truncate
  * @lstart: offset from which to truncate
  * @lend: offset to which to truncate