Cheri-research/snmalloc
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

improved comments and rename field

Browse Source 
Replaced used with needed, the number of objects needed empty this slab.

Some mild improvement to the comments.
This commit is contained in:
Matthew Parkinson
2019-11-21 09:51:50 +00:00
parent efd5228da6
commit df1dfa55db
2 changed files with 34 additions and 23 deletions
Download Patch File Download Diff File Expand all files Collapse all files

46
src/mem/metaslab.h
View File

@@ -30,13 +30,27 @@ namespace snmalloc
class Metaslab
{
public:
// Ppinter to first free entry in this slab
/**
* Pointer to first free entry in this slab
*
* The list will (allocated - needed - 1) long. The -1 is
* for the `link` element which is not in the free list.
*/
void* head;
// How many entries are not in the free list of slab.
uint16_t used = 0;
/**
* How many entries are not in the free list of slab, i.e.
* how many entries are needed to fully free this slab.
*
* In the case of a fully allocated slab, where link==1 needed
* will be 1. This enables 'return_object' to detect the slow path
* case with a single operation subtract and test.
*/
uint16_t needed = 0;
// How many entries have been allocated from this slab.
/**
* How many entries have been allocated from this slab.
*/
uint16_t allocated;
// When a slab has free space it will be on the has space list for
@@ -48,25 +62,21 @@ namespace snmalloc
// Initially zero to encode the superslabs relative list of slabs.
uint8_t next = 0;
void add_use()
{
used++;
}
/**
* Removes a use, if the slab is either
* - empty after removing the use, or
* - was full before the substraction
* Updates statistics for adding an entry to the free list, if the
* slab is either
* - empty adding the entry to the free list, or
* - was full before the subtraction
* this returns true, otherwise returns false.
**/
bool sub_use()
bool return_object()
{
return (--used) == 0;
return (--needed) == 0;
}
bool is_unused()
{
return used == 0;
return needed == 0;
}
bool is_full()
@@ -81,9 +91,9 @@ namespace snmalloc
assert(head == nullptr);
assert(link != 1);
link = 1;
// Set used to 1, so that "sub_use" will return true after calling
// Set needed to 1, so that "return_object" will return true after calling
// set_full
used = 1;
needed = 1;
}
SlabLink* get_link(Slab* slab)
@@ -192,7 +202,7 @@ namespace snmalloc
size_t size = sizeclass_to_size(sizeclass);
size_t offset = get_initial_offset(sizeclass, is_short);
size_t accounted_for = used * size + offset;
size_t accounted_for = needed * size + offset;
// Block is not full
assert(SLAB_SIZE > accounted_for);

11
src/mem/slab.h
View File

@@ -56,8 +56,9 @@ namespace snmalloc
bumpptr += meta.allocated * rsize;
if (bumpptr == SLAB_SIZE)
{
meta.add_use();
assert(meta.used == meta.allocated);
// Everything is in use, so we need all entries to be
// return before we can reclaim this slab.
meta.needed = meta.allocated;
void* link = pointer_offset(this, meta.link);
p = remove_cache_friendly_offset(link, meta.sizeclass);
@@ -119,7 +120,7 @@ namespace snmalloc
fast_free_list.value = next;
// Treat stealing the free list as allocating it all.
// Link is not in use, i.e. - 1 is required.
meta.used = meta.allocated - 1;
meta.needed = meta.allocated - 1;
p = remove_cache_friendly_offset(p, meta.sizeclass);
}
@@ -159,7 +160,7 @@ namespace snmalloc
#endif
meta.debug_slab_invariant(is_short(), this);
if (unlikely(meta.sub_use()))
if (unlikely(meta.return_object()))
return false;
// Update the head and the next pointer in the free list.
@@ -201,7 +202,7 @@ namespace snmalloc
assert(meta.head == nullptr);
// assert(meta.fully_allocated(is_short()));
meta.link = index;
meta.used = meta.allocated - 1;
meta.needed = meta.allocated - 1;
// Push on the list of slabs for this sizeclass.
sl->insert_back(meta.get_link(this));