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File 6201-Revert-erts-Stop-marking-memory-regions-as-discardab.patch of Package erlang
From 06a866734b09d636b905e2a5a3423981144119ca Mon Sep 17 00:00:00 2001 From: Lukas Larsson <lukas@erlang.org> Date: Wed, 12 Oct 2022 15:44:09 +0200 Subject: [PATCH 1/2] Revert "erts: Stop marking memory regions as discardable (`madvise(2)`)" This reverts commit df450823fcdb1657743c94023318abe3731366bb. --- erts/emulator/beam/erl_alloc_util.c | 177 ++++++++++++++++++++++++++++ erts/emulator/sys/common/erl_mmap.c | 19 +++ erts/emulator/sys/common/erl_mmap.h | 64 ++++++++++ 3 files changed, 260 insertions(+) diff --git a/erts/emulator/beam/erl_alloc_util.c b/erts/emulator/beam/erl_alloc_util.c index 84d67c3078..7f3a9b420b 100644 --- a/erts/emulator/beam/erl_alloc_util.c +++ b/erts/emulator/beam/erl_alloc_util.c @@ -2527,9 +2527,155 @@ mbc_alloc(Allctr_t *allctr, Uint size) return BLK2UMEM(blk); } +typedef struct { + char *ptr; + UWord size; +} ErtsMemDiscardRegion; + +/* Construct a discard region for the user memory of a free block, letting the + * OS reclaim its physical memory when required. + * + * Note that we're ignoring both the footer and everything that comes before + * the minimum block size as the allocator uses those areas to manage the + * block. */ +static void ERTS_INLINE +mem_discard_start(Allctr_t *allocator, Block_t *block, + ErtsMemDiscardRegion *out) +{ + UWord size = BLK_SZ(block); + + ASSERT(size >= allocator->min_block_size); + + if (size > (allocator->min_block_size + FBLK_FTR_SZ)) { + out->size = size - allocator->min_block_size - FBLK_FTR_SZ; + } else { + out->size = 0; + } + + out->ptr = (char*)block + allocator->min_block_size; +} + +/* Expands a discard region into a neighboring free block, allowing us to + * discard the block header and first page. + * + * This is very important in small-allocation scenarios where no single block + * is large enough to be discarded on its own. */ +static void ERTS_INLINE +mem_discard_coalesce(Allctr_t *allocator, Block_t *neighbor, + ErtsMemDiscardRegion *region) +{ + char *neighbor_start; + + ASSERT(IS_FREE_BLK(neighbor)); + + neighbor_start = (char*)neighbor; + + if (region->ptr >= neighbor_start) { + char *region_start_page; + + region_start_page = region->ptr - SYS_PAGE_SIZE; + region_start_page = (char*)((UWord)region_start_page & ~SYS_PAGE_SZ_MASK); + + /* Expand if our first page begins within the previous free block's + * unused data. */ + if (region_start_page >= (neighbor_start + allocator->min_block_size)) { + region->size += (region->ptr - region_start_page) - FBLK_FTR_SZ; + region->ptr = region_start_page; + } + } else { + char *region_end_page; + UWord neighbor_size; + + ASSERT(region->ptr <= neighbor_start); + + region_end_page = region->ptr + region->size + SYS_PAGE_SIZE; + region_end_page = (char*)((UWord)region_end_page & ~SYS_PAGE_SZ_MASK); + + neighbor_size = BLK_SZ(neighbor) - FBLK_FTR_SZ; + + /* Expand if our last page ends anywhere within the next free block, + * sans the footer we'll inherit. */ + if (region_end_page < neighbor_start + neighbor_size) { + region->size += region_end_page - (region->ptr + region->size); + } + } +} + +static void ERTS_INLINE +mem_discard_finish(Allctr_t *allocator, Block_t *block, + ErtsMemDiscardRegion *region) +{ +#ifdef DEBUG + char *block_start, *block_end; + UWord block_size; + + block_size = BLK_SZ(block); + + /* Ensure that the region is completely covered by the legal area of the + * free block. This must hold even when the region is too small to be + * discarded. */ + if (region->size > 0) { + ASSERT(block_size > allocator->min_block_size + FBLK_FTR_SZ); + + block_start = (char*)block + allocator->min_block_size; + block_end = (char*)block + block_size - FBLK_FTR_SZ; + + ASSERT(region->size == 0 || + (region->ptr + region->size <= block_end && + region->ptr >= block_start && + region->size <= block_size)); + } +#else + (void)allocator; + (void)block; +#endif + + if (region->size > SYS_PAGE_SIZE) { + UWord align_offset, size; + char *ptr; + + align_offset = SYS_PAGE_SIZE - ((UWord)region->ptr & SYS_PAGE_SZ_MASK); + + size = (region->size - align_offset) & ~SYS_PAGE_SZ_MASK; + ptr = region->ptr + align_offset; + + if (size > 0) { + ASSERT(!((UWord)ptr & SYS_PAGE_SZ_MASK)); + ASSERT(!(size & SYS_PAGE_SZ_MASK)); + + erts_mem_discard(ptr, size); + } + } +} + +static void +carrier_mem_discard_free_blocks(Allctr_t *allocator, Carrier_t *carrier) +{ + static const int MAX_BLOCKS_TO_DISCARD = 100; + Block_t *block; + int i; + + block = allocator->first_fblk_in_mbc(allocator, carrier); + i = 0; + + while (block != NULL && i < MAX_BLOCKS_TO_DISCARD) { + ErtsMemDiscardRegion region; + + ASSERT(IS_FREE_BLK(block)); + + mem_discard_start(allocator, block, ®ion); + mem_discard_finish(allocator, block, ®ion); + + block = allocator->next_fblk_in_mbc(allocator, carrier, block); + i++; + } +} + static void mbc_free(Allctr_t *allctr, ErtsAlcType_t type, void *p, Carrier_t **busy_pcrr_pp) { + ErtsMemDiscardRegion discard_region = {0}; + int discard; Uint is_first_blk; Uint is_last_blk; Uint blk_sz; @@ -2545,6 +2691,21 @@ mbc_free(Allctr_t *allctr, ErtsAlcType_t type, void *p, Carrier_t **busy_pcrr_pp ASSERT(IS_MBC_BLK(blk)); ASSERT(blk_sz >= allctr->min_block_size); +#ifndef DEBUG + /* We want to mark freed blocks as reclaimable to the OS, but it's a fairly + * expensive operation which doesn't do much good if we use it again soon + * after, so we limit it to deallocations on pooled carriers. */ + discard = busy_pcrr_pp && *busy_pcrr_pp; +#else + /* Always discard in debug mode, regardless of whether we're in the pool or + * not. */ + discard = 1; +#endif + + if (discard) { + mem_discard_start(allctr, blk, &discard_region); + } + HARD_CHECK_BLK_CARRIER(allctr, blk); crr = ABLK_TO_MBC(blk); @@ -2562,6 +2723,10 @@ mbc_free(Allctr_t *allctr, ErtsAlcType_t type, void *p, Carrier_t **busy_pcrr_pp blk = PREV_BLK(blk); (*allctr->unlink_free_block)(allctr, blk); + if (discard) { + mem_discard_coalesce(allctr, blk, &discard_region); + } + blk_sz += MBC_FBLK_SZ(blk); is_first_blk = IS_MBC_FIRST_FBLK(allctr, blk); SET_MBC_FBLK_SZ(blk, blk_sz); @@ -2578,6 +2743,10 @@ mbc_free(Allctr_t *allctr, ErtsAlcType_t type, void *p, Carrier_t **busy_pcrr_pp /* Coalesce with next block... */ (*allctr->unlink_free_block)(allctr, nxt_blk); + if (discard) { + mem_discard_coalesce(allctr, nxt_blk, &discard_region); + } + blk_sz += MBC_FBLK_SZ(nxt_blk); SET_MBC_FBLK_SZ(blk, blk_sz); @@ -2614,6 +2783,10 @@ mbc_free(Allctr_t *allctr, ErtsAlcType_t type, void *p, Carrier_t **busy_pcrr_pp (*allctr->link_free_block)(allctr, blk); HARD_CHECK_BLK_CARRIER(allctr, blk); + if (discard) { + mem_discard_finish(allctr, blk, &discard_region); + } + if (busy_pcrr_pp && *busy_pcrr_pp) { update_pooled_tree(allctr, crr, blk_sz); } else { @@ -3758,8 +3931,12 @@ abandon_carrier(Allctr_t *allctr, Carrier_t *crr) unlink_carrier(&allctr->mbc_list, crr); allctr->remove_mbc(allctr, crr); + /* Mark our free blocks as unused and reclaimable to the OS. */ + carrier_mem_discard_free_blocks(allctr, crr); + cpool_insert(allctr, crr); + iallctr = erts_atomic_read_nob(&crr->allctr); if (allctr == crr->cpool.orig_allctr) { /* preserve HOMECOMING flag */ -- 2.35.3
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