[RFC v2 77/83] GC: Fast garbage collection.

Andiry Xu
2018-03-10T18:22:00Z

NOVA cleans and compacts the log when the log is full.
The log is a linked list of 4KB pmem pages, and NOVA performs
fast garbage collection by deleting dead log pages (all the entries are invalid)
from the linked list.

Example:
I = Invalid, V = Valid

VIIV -> IIII -> VVII

||
|| fast gc
\/

VIIV -> VVII

Signed-off-by: Andiry Xu <jix024@cs.ucsd.edu>
---
fs/nova/Makefile | 2 +-
fs/nova/gc.c | 186 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
fs/nova/log.c | 3 +
fs/nova/nova.h | 7 +++
4 files changed, 197 insertions(+), 1 deletion(-)
create mode 100644 fs/nova/gc.c

diff --git a/fs/nova/Makefile b/fs/nova/Makefile
index 87e56c6..7a5fb6d 100644
--- a/fs/nova/Makefile
+++ b/fs/nova/Makefile
@@ -4,5 +4,5 @@

obj-$(CONFIG_NOVA_FS) += nova.o

-nova-y := balloc.o bbuild.o dax.o dir.o file.o inode.o ioctl.o journal.o\
+nova-y := balloc.o bbuild.o dax.o dir.o file.o gc.o inode.o ioctl.o journal.o\
log.o namei.o rebuild.o stats.o super.o symlink.o
diff --git a/fs/nova/gc.c b/fs/nova/gc.c
new file mode 100644
index 0000000..1634c04
--- /dev/null
+++ b/fs/nova/gc.c
@@ -0,0 +1,186 @@
+/*
+ * BRIEF DESCRIPTION
+ *
+ * Garbage collection methods
+ *
+ * Copyright 2015-2016 Regents of the University of California,
+ * UCSD Non-Volatile Systems Lab, Andiry Xu <jix024@cs.ucsd.edu>
+ * Copyright 2012-2013 Intel Corporation
+ * Copyright 2009-2011 Marco Stornelli <marco.stornelli@gmail.com>
+ * Copyright 2003 Sony Corporation
+ * Copyright 2003 Matsushita Electric Industrial Co., Ltd.
+ * 2003-2004 (c) MontaVista Software, Inc. , Steve Longerbeam
+ * This file is licensed under the terms of the GNU General Public
+ * License version 2. This program is licensed "as is" without any
+ * warranty of any kind, whether express or implied.
+ */
+
+#include "nova.h"
+#include "inode.h"
+
+
+static bool curr_page_invalid(struct super_block *sb,
+ struct nova_inode *pi, struct nova_inode_info_header *sih,
+ u64 page_head)
+{
+ struct nova_inode_log_page *curr_page;
+ struct nova_inode_page_tail page_tail;
+ unsigned int num_entries;
+ unsigned int invalid_entries;
+ bool ret;
+ timing_t check_time;
+ int rc;
+
+ NOVA_START_TIMING(check_invalid_t, check_time);
+
+ curr_page = (struct nova_inode_log_page *)
+ nova_get_block(sb, page_head);
+ rc = memcpy_mcsafe(&page_tail, &curr_page->page_tail,
+ sizeof(struct nova_inode_page_tail));
+ if (rc) {
+ nova_err(sb, "check page failed\n");
+ return false;
+ }
+
+ num_entries = le32_to_cpu(page_tail.num_entries);
+ invalid_entries = le32_to_cpu(page_tail.invalid_entries);
+
+ ret = (invalid_entries == num_entries);
+ if (!ret) {
+ sih->num_entries += num_entries;
+ sih->valid_entries += num_entries - invalid_entries;
+ }
+
+ NOVA_END_TIMING(check_invalid_t, check_time);
+ return ret;
+}
+
+static void free_curr_page(struct super_block *sb,
+ struct nova_inode_info_header *sih,
+ struct nova_inode_log_page *curr_page,
+ struct nova_inode_log_page *last_page, u64 curr_head)
+{
+ u8 btype = sih->i_blk_type;
+
+ nova_set_next_page_address(sb, last_page,
+ curr_page->page_tail.next_page, 1);
+ nova_free_log_blocks(sb, sih,
+ nova_get_blocknr(sb, curr_head, btype), 1);
+}
+
+
+/*
+ * Scan pages in the log and remove those with no valid log entries.
+ */
+int nova_inode_log_fast_gc(struct super_block *sb,
+ struct nova_inode *pi, struct nova_inode_info_header *sih,
+ u64 curr_tail, u64 new_block,
+ int num_pages, int force_thorough)
+{
+ u64 curr, next, possible_head = 0;
+ int found_head = 0;
+ struct nova_inode_log_page *last_page = NULL;
+ struct nova_inode_log_page *curr_page = NULL;
+ int first_need_free = 0;
+ int num_logs;
+ u8 btype = sih->i_blk_type;
+ unsigned long blocks;
+ unsigned long checked_pages = 0;
+ int freed_pages = 0;
+ timing_t gc_time;
+
+ NOVA_START_TIMING(fast_gc_t, gc_time);
+ curr = sih->log_head;
+ sih->valid_entries = 0;
+ sih->num_entries = 0;
+
+ num_logs = 1;
+
+ nova_dbgv("%s: log head 0x%llx, tail 0x%llx\n",
+ __func__, curr, curr_tail);
+ while (1) {
+ if (curr >> PAGE_SHIFT == sih->log_tail >> PAGE_SHIFT) {
+ /* Don't recycle tail page */
+ if (found_head == 0) {
+ possible_head = cpu_to_le64(curr);
+ }
+ break;
+ }
+
+ curr_page = (struct nova_inode_log_page *)
+ nova_get_block(sb, curr);
+ next = next_log_page(sb, curr);
+ if (next < 0)
+ break;
+
+ nova_dbg_verbose("curr 0x%llx, next 0x%llx\n", curr, next);
+ if (curr_page_invalid(sb, pi, sih, curr)) {
+ nova_dbg_verbose("curr page %p invalid\n", curr_page);
+ if (curr == sih->log_head) {
+ /* Free first page later */
+ first_need_free = 1;
+ last_page = curr_page;
+ } else {
+ nova_dbg_verbose("Free log block 0x%llx\n",
+ curr >> PAGE_SHIFT);
+ free_curr_page(sb, sih, curr_page, last_page,
+ curr);
+ }
+ NOVA_STATS_ADD(fast_gc_pages, 1);
+ freed_pages++;
+ } else {
+ if (found_head == 0) {
+ possible_head = cpu_to_le64(curr);
+ found_head = 1;
+ }
+ last_page = curr_page;
+ }
+
+ curr = next;
+ checked_pages++;
+ if (curr == 0)
+ break;
+ }
+
+ NOVA_STATS_ADD(fast_checked_pages, checked_pages);
+ nova_dbgv("checked pages %lu, freed %d\n", checked_pages, freed_pages);
+ checked_pages -= freed_pages;
+
+ // TODO: I think this belongs in nova_extend_inode_log.
+ if (num_pages > 0) {
+ curr = BLOCK_OFF(curr_tail);
+ curr_page = (struct nova_inode_log_page *)
+ nova_get_block(sb, curr);
+
+ nova_set_next_page_address(sb, curr_page, new_block, 1);
+ }
+
+ curr = sih->log_head;
+
+ pi->log_head = possible_head;
+ nova_persist_inode(pi);
+ sih->log_head = possible_head;
+ nova_dbgv("%s: %d new head 0x%llx\n", __func__,
+ found_head, possible_head);
+ sih->log_pages += (num_pages - freed_pages) * num_logs;
+ /* Don't update log tail pointer here */
+ nova_flush_buffer(&pi->log_head, CACHELINE_SIZE, 1);
+
+ if (first_need_free) {
+ nova_dbg_verbose("Free log head block 0x%llx\n",
+ curr >> PAGE_SHIFT);
+ nova_free_log_blocks(sb, sih,
+ nova_get_blocknr(sb, curr, btype), 1);
+ }
+
+ NOVA_END_TIMING(fast_gc_t, gc_time);
+
+ if (sih->num_entries == 0)
+ return 0;
+
+ blocks = (sih->valid_entries * checked_pages) / sih->num_entries;
+ if ((sih->valid_entries * checked_pages) % sih->num_entries)
+ blocks++;
+
+ return 0;
+}
diff --git a/fs/nova/log.c b/fs/nova/log.c
index 451be27..66bf98e 100644
--- a/fs/nova/log.c
+++ b/fs/nova/log.c
@@ -964,6 +964,9 @@ static u64 nova_extend_inode_log(struct super_block *sb, struct nova_inode *pi,
}

/* Perform GC */
+ nova_inode_log_fast_gc(sb, pi, sih, curr_p,
+ new_block, allocated, 0);
+
return new_block;
}

diff --git a/fs/nova/nova.h b/fs/nova/nova.h
index ab9153e..32b7b2f 100644
--- a/fs/nova/nova.h
+++ b/fs/nova/nova.h
@@ -515,6 +515,13 @@ int nova_remove_dentry(struct dentry *dentry, int dec_link,
extern const struct file_operations nova_dax_file_operations;
extern const struct inode_operations nova_file_inode_operations;

+
+/* gc.c */
+int nova_inode_log_fast_gc(struct super_block *sb,
+ struct nova_inode *pi, struct nova_inode_info_header *sih,
+ u64 curr_tail, u64 new_block, int num_pages,
+ int force_thorough);
+
/* ioctl.c */
extern long nova_ioctl(struct file *filp, unsigned int cmd, unsigned long arg);
#ifdef CONFIG_COMPAT
--
2.7.4