Author: Armin Rigo <[email protected]>
Branch: minimark-no-mass-free
Changeset: r47971:3e89774d7da6
Date: 2011-10-12 14:20 +0200
http://bitbucket.org/pypy/pypy/changeset/3e89774d7da6/
Log: Comments.
diff --git a/pypy/rpython/memory/gc/minimark.py
b/pypy/rpython/memory/gc/minimark.py
--- a/pypy/rpython/memory/gc/minimark.py
+++ b/pypy/rpython/memory/gc/minimark.py
@@ -183,7 +183,7 @@
# that are larger are just allocated with raw_malloc(). Note that
# the size limit for being first allocated in the nursery is much
# larger; see below.
- "small_request_threshold": 35*WORD,
+ "small_request_threshold": 43*WORD,
# Full collection threshold: after a major collection, we record
# the total size consumed; and after every minor collection, if the
diff --git a/pypy/rpython/memory/gc/minimarkpage.py
b/pypy/rpython/memory/gc/minimarkpage.py
--- a/pypy/rpython/memory/gc/minimarkpage.py
+++ b/pypy/rpython/memory/gc/minimarkpage.py
@@ -21,20 +21,36 @@
# already marked.
#
# reset_stop()
-# Leaves the "resetting" state. All objects on which still_in_use()
-# was not called are considered as free.
+# Leaves the "resetting" state. All objects on which
+# mark_still_in_use() was not called are considered as free.
#
# total_memory_used
# A r_uint. Not valid in the resetting state.
#
-# This is done by keeping one bit per object, in off-object bitfields
-# (to speed up looking for a free bit and to be more fork()-friendly).
-# Initially OFF=0 and ON=1. malloc() finds an old location which is
-# OFF, and mark it as ON. reset_start() finds all locations still at
-# OFF and returns to the OS completely OFF arenas, and mark all
-# remaining bits as ON. Then it switches the meaning of ON and OFF, so
-# that all bits are instantly OFF. mark_still_in_use() marks the bit as
-# ON again.
+# This is done by keeping one bit per object in off-object bitfields (to
+# speed up looking for a free bit and to be more fork()-friendly).
+# mark_still_in_use() marks the bit as ON ("mark" phase). Then later
+# malloc() lazily "sweeps" the bits: any location about which the bit is
+# ON is reset to OFF, and the first location about which the bit is
+# already OFF is returned as the result of malloc(). The lazy sweep is
+# completed in reset_start(), which if necessary finishes the sweep to
+# reset ON bits to OFF and to return to the OS arenas that were already
+# completely OFF.
+#
+# A "page" is 1024 WORDs, and an "arena" is 131072 WORDs, i.e. 128
+# pages. Each page is either free or contains objects all of the same
+# size. The sizes handled by the ArenaCollection are between WORD and
+# 42*WORD. The mapping from an object position to a bit is done at a
+# granularity of 2*WORD bytes, so that we need 1024/2 = 512 bits = 64
+# bytes per page or 8192 bytes per arena. We reserve the first 1 or 2
+# pages of the arena for the bits, leaving 64 or 128 bytes free at the
+# start of the arena for random fields.
+#
+# The granularity of two WORDs is ok because a single-WORD object cannot
+# possibly contain further pointers. We choose this fixed granularity
+# instead of, more naturally, one bit per object, because computing this
+# would involve dividing the offset by the size.
+#
# ____________________________________________________________
#
@@ -50,25 +66,20 @@
# The actual allocation occurs in whole arenas, which are then subdivided
# into pages. For each arena we allocate one of the following structures:
-def get_arena_type(num_words):
- ARENA_PTR = lltype.Ptr(lltype.ForwardReference())
- ARENA = lltype.Struct('ArenaReference',
- # --- One bit per "basic unit" of size in the whole arena, set if
- # --- this basic unit contains the start of a live object. "Basic
- # --- unit" is 2 WORDs by default.
- ('usage_bits', lltype.FixedSizeArray(lltype.Unsigned, num_words)),
- # -- The address of the arena, as returned by malloc()
- ('base', llmemory.Address),
- # -- The number of free and the total number of pages in the arena
- ('nfreepages', lltype.Signed),
- ('totalpages', lltype.Signed),
- # -- A chained list of free pages in the arena. Ends with NULL.
- ('freepages', llmemory.Address),
- # -- A linked list of arenas. See below.
- ('nextarena', ARENA_PTR),
- )
- ARENA_PTR.TO.become(ARENA)
- return ARENA
+ARENA_PTR = lltype.Ptr(lltype.ForwardReference())
+ARENA = lltype.Struct('ArenaReference',
+ # -- The address of the arena, as returned by malloc()
+ ('base', llmemory.Address),
+ # -- The number of free and the total number of pages in the arena
+ ('nfreepages', lltype.Signed),
+ ('totalpages', lltype.Signed),
+ # -- A chained list of free pages in the arena. Ends with NULL.
+ ('freepages', llmemory.Address),
+ # -- A linked list of arenas. See below.
+ ('nextarena', ARENA_PTR),
+ )
+ARENA_PTR.TO.become(ARENA)
+ARENA_NULL = lltype.nullptr(ARENA)
# The idea is that when we need a free page, we take it from the arena
# which currently has the *lowest* number of free pages. This allows
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