[PATCH 1/2] ntdll: Introduce free_ranges indexing sequence.
Rémi Bernon
rbernon at codeweavers.com
Fri Apr 10 04:55:37 CDT 2020
This is an ordered range sequence used to keep track of free address
ranges.
The sequence contains an entry for every free address range, with base
pointing to the first free address and end pointing to the next first
used address. It is initialized to [0, ~0] for convenience, so that
there's always a range before or after a view.
In the worst case scenario, where memory is entirely fragmented, there's
going to be one more range than allocated views, but in general there's
much less. In any case, because of cache locality, iterating in the
contiguous sequence is much faster than traversing the view rbtree.
In theory there can be a performance hit when allocating or deleting a
view, as we may have to move the end of the sequence when a range is
split or merged. But in practice and given the usually low number of
ranges, this is not an issue.
The default and maximum sequence size can hold up to 65536 ranges, which
is much more than enough in general, and performance is probably going
to be bad before reaching the limit anyway. The code currently asserts
when reaching the limit, although we could possibly grow the sequence.
Signed-off-by: Rémi Bernon <rbernon at codeweavers.com>
---
Notes:
Tracking free ranges over the whole address space can increase the
free range count significantly, if pages are getting allocated outside
of the reserved areas, because of the mmap/VirtualAlloc alignment
adjustments. We don't use the free ranges outside of the reserved areas
for now so we just skip these instead.
We also reduce fragmentation by aligning free ranges boundaries to 64k,
as it is the default view alignment. I'm not sure if that has other
implications aside from wasting a bit of address space. [1]
In We Happy Few, the maximum number of unique free ranges after starting
a new game, for a maximum of ~=17k allocated views of which ~=9k are in
reserved memory:
* Tracking the whole memory: ~=8k ranges
* Tracking reserved memory: ~=600 ranges
* Tracking reserved memory and align to 64k: ~=400 ranges
By comparison, although it varies from a game to another, in other games
the number of allocated views is usually within 500-2k, and the number
of ranges roughly follows the number of views. Tracking only reserved
areas makes it follow the number of views there instead, but it is the
most common case. Aligning free ranges to 64k then reduces the ranges
count to ~=50.
In any case performance doesn't seem to differ a lot and every scenario
has roughly the same performance gain. Even with the high fragmentation,
the cache locality is good enough to mitigate the performance hit and to
be better than the tree traversal.
[1] It looks like most allocations are done with the default 64k align,
but some others aren't and are using the internal virtual_alloc_aligned.
The TEBs and signal stacks doesn't seem too much of a waste, but the
heap large blocks, allocated with a 16b align - internally converted to
4k align - may be impacted.
dlls/ntdll/virtual.c | 170 ++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 167 insertions(+), 3 deletions(-)
diff --git a/dlls/ntdll/virtual.c b/dlls/ntdll/virtual.c
index 6ad2d21e01e..3740d1a4457 100644
--- a/dlls/ntdll/virtual.c
+++ b/dlls/ntdll/virtual.c
@@ -122,6 +122,7 @@ static RTL_CRITICAL_SECTION csVirtual = { &critsect_debug, -1, 0, 0, 0, 0 };
#ifdef __i386__
static const UINT page_shift = 12;
static const UINT_PTR page_mask = 0xfff;
+static const UINT_PTR free_ranges_mask = 0xffff;
/* Note: these are Windows limits, you cannot change them. */
static void *address_space_limit = (void *)0xc0000000; /* top of the total available address space */
static void *user_space_limit = (void *)0x7fff0000; /* top of the user address space */
@@ -130,6 +131,7 @@ static void *address_space_start = (void *)0x110000; /* keep DOS area clear *
#elif defined(__x86_64__)
static const UINT page_shift = 12;
static const UINT_PTR page_mask = 0xfff;
+static const UINT_PTR free_ranges_mask = 0xffff;
static void *address_space_limit = (void *)0x7fffffff0000;
static void *user_space_limit = (void *)0x7fffffff0000;
static void *working_set_limit = (void *)0x7fffffff0000;
@@ -137,6 +139,7 @@ static void *address_space_start = (void *)0x10000;
#elif defined(__arm__)
static const UINT page_shift = 12;
static const UINT_PTR page_mask = 0xfff;
+static const UINT_PTR free_ranges_mask = 0xffff;
static void *address_space_limit = (void *)0xc0000000;
static void *user_space_limit = (void *)0x7fff0000;
static void *working_set_limit = (void *)0x7fff0000;
@@ -144,6 +147,7 @@ static void *address_space_start = (void *)0x10000;
#elif defined(__aarch64__)
static const UINT page_shift = 12;
static const UINT_PTR page_mask = 0xfff;
+static const UINT_PTR free_ranges_mask = 0xffff;
static void *address_space_limit = (void *)0xffffffff0000;
static void *user_space_limit = (void *)0x7fffffff0000;
static void *working_set_limit = (void *)0x7fffffff0000;
@@ -152,6 +156,7 @@ static void *address_space_start = (void *)0x10000;
UINT_PTR page_size = 0;
static UINT page_shift;
static UINT_PTR page_mask;
+static UINT_PTR free_ranges_mask;
static void *address_space_limit;
static void *user_space_limit;
static void *working_set_limit;
@@ -184,6 +189,156 @@ static void *preload_reserve_end;
static BOOL use_locks;
static BOOL force_exec_prot; /* whether to force PROT_EXEC on all PROT_READ mmaps */
+struct range_entry
+{
+ void *base;
+ void *end;
+};
+
+static struct range_entry *free_ranges;
+static struct range_entry *free_ranges_end;
+
+
+/***********************************************************************
+ * free_ranges_lower_bound
+ *
+ * Returns the first range whose end is not less than addr, or end if there's none.
+ */
+static struct range_entry *free_ranges_lower_bound( void *addr )
+{
+ struct range_entry *begin = free_ranges;
+ struct range_entry *end = free_ranges_end;
+ struct range_entry *mid;
+
+ while (begin < end)
+ {
+ mid = begin + (end - begin) / 2;
+ if (mid->end < addr)
+ begin = mid + 1;
+ else
+ end = mid;
+ }
+
+ return begin;
+}
+
+
+/***********************************************************************
+ * free_ranges_insert_view
+ *
+ * Updates the free_ranges after a new view has been created.
+ */
+static void free_ranges_insert_view( struct file_view *view )
+{
+ void *view_base = ROUND_ADDR( view->base, free_ranges_mask );
+ void *view_end = ROUND_ADDR( (char *)view->base + view->size + free_ranges_mask, free_ranges_mask );
+ struct range_entry *range = free_ranges_lower_bound( view_base );
+ struct range_entry *next = range + 1;
+
+ /* free_ranges initial value is such that the view is either inside range or before another one. */
+ assert( range != free_ranges_end );
+ assert( range->end > view_base || next != free_ranges_end );
+
+ /* this happens because virtual_alloc_thread_stack shrinks a view, then creates another one on top */
+ if ((range->end > view_base && range->base >= view_end) ||
+ (range->end == view_base && next->base >= view_end))
+ {
+ WARN( "range %p - %p is already mapped\n", view_base, view_end );
+ return;
+ }
+
+ /* this should never happen */
+ if (range->base > view_base || range->end < view_end)
+ ERR( "range %p - %p is already partially mapped\n", view_base, view_end );
+ assert( range->base <= view_base && range->end >= view_end );
+
+ /* need to split the range in two */
+ if (range->base < view_base && range->end > view_end)
+ {
+ memmove( next + 1, next, (free_ranges_end - next) * sizeof(struct range_entry) );
+ free_ranges_end += 1;
+ if ((char *)free_ranges_end - (char *)free_ranges > view_block_size)
+ MESSAGE( "Free range sequence is full, trouble ahead!\n" );
+ assert( (char *)free_ranges_end - (char *)free_ranges <= view_block_size );
+
+ next->base = view_end;
+ next->end = range->end;
+ range->end = view_base;
+ }
+ else
+ {
+ /* otherwise we just have to shrink it */
+ if (range->base < view_base)
+ range->end = view_base;
+ else
+ range->base = view_end;
+
+ if (range->base < range->end) return;
+
+ /* and possibly remove it if it's now empty */
+ memmove( range, next, (free_ranges_end - next) * sizeof(struct range_entry) );
+ free_ranges_end -= 1;
+ assert( free_ranges_end - free_ranges > 0 );
+ }
+}
+
+
+/***********************************************************************
+ * free_ranges_remove_view
+ *
+ * Updates the free_ranges after a view has been destroyed.
+ */
+static void free_ranges_remove_view( struct file_view *view )
+{
+ void *view_base = ROUND_ADDR( view->base, free_ranges_mask );
+ void *view_end = ROUND_ADDR( (char *)view->base + view->size + free_ranges_mask, free_ranges_mask );
+ struct range_entry *range = free_ranges_lower_bound( view_base );
+ struct range_entry *next = range + 1;
+
+ /* free_ranges initial value is such that the view is either inside range or before another one. */
+ assert( range != free_ranges_end );
+ assert( range->end > view_base || next != free_ranges_end );
+
+ /* this should never happen, but we can safely ignore it */
+ if (range->base <= view_base && range->end >= view_end)
+ {
+ WARN( "range %p - %p is already unmapped\n", view_base, view_end );
+ return;
+ }
+
+ /* this should never happen */
+ if (range->base < view_end && range->end > view_base)
+ ERR( "range %p - %p is already partially unmapped\n", view_base, view_end );
+ assert( range->end <= view_base || range->base >= view_end );
+
+ /* merge with next if possible */
+ if (range->end == view_base && next->base == view_end)
+ {
+ range->end = next->end;
+ memmove( next, next + 1, (free_ranges_end - next - 1) * sizeof(struct range_entry) );
+ free_ranges_end -= 1;
+ assert( free_ranges_end - free_ranges > 0 );
+ }
+ /* or try growing the range */
+ else if (range->end == view_base)
+ range->end = view_end;
+ else if (range->base == view_end)
+ range->base = view_base;
+ /* otherwise create a new one */
+ else
+ {
+ memmove( range + 1, range, (free_ranges_end - range) * sizeof(struct range_entry) );
+ free_ranges_end += 1;
+ if ((char *)free_ranges_end - (char *)free_ranges > view_block_size)
+ MESSAGE( "Free range sequence is full, trouble ahead!\n" );
+ assert( (char *)free_ranges_end - (char *)free_ranges <= view_block_size );
+
+ range->base = view_base;
+ range->end = view_end;
+ }
+}
+
+
static inline int is_view_valloc( const struct file_view *view )
{
return !(view->protect & (SEC_FILE | SEC_RESERVE | SEC_COMMIT));
@@ -835,6 +990,8 @@ static void delete_view( struct file_view *view ) /* [in] View */
{
if (!(view->protect & VPROT_SYSTEM)) unmap_area( view->base, view->size );
set_page_vprot( view->base, view->size, 0 );
+ if (wine_mmap_is_in_reserved_area( view->base, view->size ))
+ free_ranges_remove_view( view );
wine_rb_remove( &views_tree, &view->entry );
*(struct file_view **)view = next_free_view;
next_free_view = view;
@@ -882,6 +1039,8 @@ static NTSTATUS create_view( struct file_view **view_ret, void *base, size_t siz
set_page_vprot( base, size, vprot );
wine_rb_put( &views_tree, view->base, &view->entry );
+ if (wine_mmap_is_in_reserved_area( view->base, view->size ))
+ free_ranges_insert_view( view );
*view_ret = view;
@@ -1977,9 +2136,9 @@ void virtual_init(void)
/* try to find space in a reserved area for the views and pages protection table */
#ifdef _WIN64
pages_vprot_size = ((size_t)address_space_limit >> page_shift >> pages_vprot_shift) + 1;
- alloc_views.size = view_block_size + pages_vprot_size * sizeof(*pages_vprot);
+ alloc_views.size = 2 * view_block_size + pages_vprot_size * sizeof(*pages_vprot);
#else
- alloc_views.size = view_block_size + (1U << (32 - page_shift));
+ alloc_views.size = 2 * view_block_size + (1U << (32 - page_shift));
#endif
if (wine_mmap_enum_reserved_areas( alloc_virtual_heap, &alloc_views, 1 ))
wine_mmap_remove_reserved_area( alloc_views.base, alloc_views.size, 0 );
@@ -1989,9 +2148,14 @@ void virtual_init(void)
assert( alloc_views.base != (void *)-1 );
view_block_start = alloc_views.base;
view_block_end = view_block_start + view_block_size / sizeof(*view_block_start);
- pages_vprot = (void *)((char *)alloc_views.base + view_block_size);
+ free_ranges = (void *)((char *)alloc_views.base + view_block_size);
+ pages_vprot = (void *)((char *)alloc_views.base + 2 * view_block_size);
wine_rb_init( &views_tree, compare_view );
+ free_ranges[0].base = (void *)0;
+ free_ranges[0].end = (void *)~0;
+ free_ranges_end = free_ranges + 1;
+
/* make the DOS area accessible (except the low 64K) to hide bugs in broken apps like Excel 2003 */
size = (char *)address_space_start - (char *)0x10000;
if (size && wine_mmap_is_in_reserved_area( (void*)0x10000, size ) == 1)
--
2.26.0
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