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Implement retain on Windows.

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The VirtualAlloc and VirtualFree APIs are different because MEM_DECOMMIT cannot
be used across multiple VirtualAlloc regions.  To properly support decommit,
only allow merge / split within the same region -- this is done by tracking the
"is_head" state of extents and not merging cross-region.

Add a new state is_head (only relevant for retain && !maps_coalesce), which is
true for the first extent in each VirtualAlloc region.  Determine if two extents
can be merged based on the head state, and use serial numbers for sanity checks.
This commit is contained in:
Qi Wang
2019-07-12 16:20:23 -07:00
committed by Qi Wang
parent f32f23d6cc
commit 9a86c65abc
8 changed files with 110 additions and 28 deletions
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76
src/extent.c
View File

@@ -50,20 +50,16 @@ static bool extent_purge_forced_default(extent_hooks_t *extent_hooks,
static bool extent_purge_forced_impl(tsdn_t *tsdn, arena_t *arena,
extent_hooks_t **r_extent_hooks, extent_t *extent, size_t offset,
size_t length, bool growing_retained);
#ifdef JEMALLOC_MAPS_COALESCE
static bool extent_split_default(extent_hooks_t *extent_hooks, void *addr,
size_t size, size_t size_a, size_t size_b, bool committed,
unsigned arena_ind);
#endif
static extent_t *extent_split_impl(tsdn_t *tsdn, arena_t *arena,
extent_hooks_t **r_extent_hooks, extent_t *extent, size_t size_a,
szind_t szind_a, bool slab_a, size_t size_b, szind_t szind_b, bool slab_b,
bool growing_retained);
#ifdef JEMALLOC_MAPS_COALESCE
static bool extent_merge_default(extent_hooks_t *extent_hooks, void *addr_a,
size_t size_a, void *addr_b, size_t size_b, bool committed,
unsigned arena_ind);
#endif
static bool extent_merge_impl(tsdn_t *tsdn, arena_t *arena,
extent_hooks_t **r_extent_hooks, extent_t *a, extent_t *b,
bool growing_retained);
@@ -88,11 +84,9 @@ const extent_hooks_t extent_hooks_default = {
,
NULL
#endif
#ifdef JEMALLOC_MAPS_COALESCE
,
extent_split_default,
extent_merge_default
#endif
};
/* Used exclusively for gdump triggering. */
@@ -1323,7 +1317,7 @@ extent_grow_retained(tsdn_t *tsdn, arena_t *arena,
extent_init(extent, arena, ptr, alloc_size, false, SC_NSIZES,
arena_extent_sn_next(arena), extent_state_active, zeroed,
committed, true);
committed, true, EXTENT_IS_HEAD);
if (ptr == NULL) {
extent_dalloc(tsdn, arena, extent);
goto label_err;
@@ -1495,7 +1489,7 @@ extent_alloc_wrapper_hard(tsdn_t *tsdn, arena_t *arena,
}
extent_init(extent, arena, addr, esize, slab, szind,
arena_extent_sn_next(arena), extent_state_active, *zero, *commit,
true);
true, EXTENT_NOT_HEAD);
if (pad != 0) {
extent_addr_randomize(tsdn, extent, alignment);
}
@@ -2045,13 +2039,20 @@ extent_purge_forced_wrapper(tsdn_t *tsdn, arena_t *arena,
offset, length, false);
}
#ifdef JEMALLOC_MAPS_COALESCE
static bool
extent_split_default(extent_hooks_t *extent_hooks, void *addr, size_t size,
size_t size_a, size_t size_b, bool committed, unsigned arena_ind) {
return !maps_coalesce;
if (!maps_coalesce) {
/*
* Without retain, only whole regions can be purged (required by
* MEM_RELEASE on Windows) -- therefore disallow splitting. See
* comments in extent_head_no_merge().
*/
return !opt_retain;
}
return false;
}
#endif
/*
* Accepts the extent to split, and the characteristics of each side of the
@@ -2083,7 +2084,8 @@ extent_split_impl(tsdn_t *tsdn, arena_t *arena,
extent_init(trail, arena, (void *)((uintptr_t)extent_base_get(extent) +
size_a), size_b, slab_b, szind_b, extent_sn_get(extent),
extent_state_get(extent), extent_zeroed_get(extent),
extent_committed_get(extent), extent_dumpable_get(extent));
extent_committed_get(extent), extent_dumpable_get(extent),
EXTENT_NOT_HEAD);
rtree_ctx_t rtree_ctx_fallback;
rtree_ctx_t *rtree_ctx = tsdn_rtree_ctx(tsdn, &rtree_ctx_fallback);
@@ -2094,7 +2096,8 @@ extent_split_impl(tsdn_t *tsdn, arena_t *arena,
extent_init(&lead, arena, extent_addr_get(extent), size_a,
slab_a, szind_a, extent_sn_get(extent),
extent_state_get(extent), extent_zeroed_get(extent),
extent_committed_get(extent), extent_dumpable_get(extent));
extent_committed_get(extent), extent_dumpable_get(extent),
EXTENT_NOT_HEAD);
extent_rtree_leaf_elms_lookup(tsdn, rtree_ctx, &lead, false,
true, &lead_elm_a, &lead_elm_b);
@@ -2152,7 +2155,7 @@ extent_split_wrapper(tsdn_t *tsdn, arena_t *arena,
static bool
extent_merge_default_impl(void *addr_a, void *addr_b) {
if (!maps_coalesce) {
if (!maps_coalesce && !opt_retain) {
return true;
}
if (have_dss && !extent_dss_mergeable(addr_a, addr_b)) {
@@ -2162,13 +2165,51 @@ extent_merge_default_impl(void *addr_a, void *addr_b) {
return false;
}
#ifdef JEMALLOC_MAPS_COALESCE
/*
* Returns true if the given extents can't be merged because of their head bit
* settings. Assumes the second extent has the higher address.
*/
static bool
extent_head_no_merge(extent_t *a, extent_t *b) {
assert(extent_base_get(a) < extent_base_get(b));
/*
* When coalesce is not always allowed (Windows), only merge extents
* from the same VirtualAlloc region under opt.retain (in which case
* MEM_DECOMMIT is utilized for purging).
*/
if (maps_coalesce) {
return false;
}
if (!opt_retain) {
return true;
}
/* If b is a head extent, disallow the cross-region merge. */
if (extent_is_head_get(b)) {
/*
* Additionally, sn should not overflow with retain; sanity
* check that different regions have unique sn.
*/
assert(extent_sn_comp(a, b) != 0);
return true;
}
assert(extent_sn_comp(a, b) == 0);
return false;
}
static bool
extent_merge_default(extent_hooks_t *extent_hooks, void *addr_a, size_t size_a,
void *addr_b, size_t size_b, bool committed, unsigned arena_ind) {
if (!maps_coalesce) {
tsdn_t *tsdn = tsdn_fetch();
extent_t *a = iealloc(tsdn, addr_a);
extent_t *b = iealloc(tsdn, addr_b);
if (extent_head_no_merge(a, b)) {
return true;
}
}
return extent_merge_default_impl(addr_a, addr_b);
}
#endif
static bool
extent_merge_impl(tsdn_t *tsdn, arena_t *arena,
@@ -2176,10 +2217,11 @@ extent_merge_impl(tsdn_t *tsdn, arena_t *arena,
bool growing_retained) {
witness_assert_depth_to_rank(tsdn_witness_tsdp_get(tsdn),
WITNESS_RANK_CORE, growing_retained ? 1 : 0);
assert(extent_base_get(a) < extent_base_get(b));
extent_hooks_assure_initialized(arena, r_extent_hooks);
if ((*r_extent_hooks)->merge == NULL) {
if ((*r_extent_hooks)->merge == NULL || extent_head_no_merge(a, b)) {
return true;
}

5
src/extent_dss.c
View File

@@ -156,7 +156,8 @@ extent_alloc_dss(tsdn_t *tsdn, arena_t *arena, void *new_addr, size_t size,
extent_init(gap, arena, gap_addr_page,
gap_size_page, false, SC_NSIZES,
arena_extent_sn_next(arena),
extent_state_active, false, true, true);
extent_state_active, false, true, true,
EXTENT_NOT_HEAD);
}
/*
* Compute the address just past the end of the desired
@@ -200,7 +201,7 @@ extent_alloc_dss(tsdn_t *tsdn, arena_t *arena, void *new_addr, size_t size,
extent_init(&extent, arena, ret, size,
size, false, SC_NSIZES,
extent_state_active, false, true,
true);
true, EXTENT_NOT_HEAD);
if (extent_purge_forced_wrapper(tsdn,
arena, &extent_hooks, &extent, 0,
size)) {