1 // Copyright 2020 The Pigweed Authors
3 // Licensed under the Apache License, Version 2.0 (the "License"); you may not
4 // use this file except in compliance with the License. You may obtain a copy of
7 // https://www.apache.org/licenses/LICENSE-2.0
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
11 // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
12 // License for the specific language governing permissions and limitations under
15 #define PW_LOG_MODULE_NAME "KVS"
16 #define PW_LOG_LEVEL PW_KVS_LOG_LEVEL
17 #define PW_LOG_USE_ULTRA_SHORT_NAMES 1
19 #include "pw_kvs/internal/sectors.h"
21 #include "pw_kvs_private/config.h"
22 #include "pw_log/log.h"
24 namespace pw::kvs::internal {
27 // Returns true if the container conatins the value.
28 // TODO: At some point move this to pw_containers, along with adding tests.
29 template <typename Container, typename T>
30 bool Contains(const Container& container, const T& value) {
31 return std::find(std::begin(container), std::end(container), value) !=
37 Status Sectors::Find(FindMode find_mode,
38 SectorDescriptor** found_sector,
40 std::span<const Address> addresses_to_skip,
41 std::span<const Address> reserved_addresses) {
42 SectorDescriptor* first_empty_sector = nullptr;
43 bool at_least_two_empty_sectors = (find_mode == kGarbageCollect);
45 // Used for the GC reclaimable bytes check
46 SectorDescriptor* non_empty_least_reclaimable_sector = nullptr;
47 const size_t sector_size_bytes = partition_.sector_size_bytes();
49 // Build a list of sectors to avoid.
51 // This is overly strict. reserved_addresses is populated when there are
52 // sectors reserved for a new entry. It is safe to garbage collect into
53 // these sectors, as long as there remains room for the pending entry. These
54 // reserved sectors could also be garbage collected if they have recoverable
55 // space. For simplicitly, avoid both the relocating key's redundant entries
56 // (addresses_to_skip) and the sectors reserved for pending writes
57 // (reserved_addresses).
58 // TODO(hepler): Look into improving garbage collection.
59 size_t sectors_to_skip = 0;
60 for (Address address : addresses_to_skip) {
61 temp_sectors_to_skip_[sectors_to_skip++] = &FromAddress(address);
63 for (Address address : reserved_addresses) {
64 temp_sectors_to_skip_[sectors_to_skip++] = &FromAddress(address);
67 DBG("Find sector with %u bytes available, starting with sector %u, %s",
70 (find_mode == kAppendEntry) ? "Append" : "GC");
71 for (size_t i = 0; i < sectors_to_skip; ++i) {
72 DBG(" Skip sector %u", Index(temp_sectors_to_skip_[i]));
75 // last_new_ is the sector that was last selected as the "new empty sector" to
76 // write to. This last new sector is used as the starting point for the next
77 // "find a new empty sector to write to" operation. By using the last new
78 // sector as the start point we will cycle which empty sector is selected
79 // next, spreading the wear across all the empty sectors and get a wear
80 // leveling benefit, rather than putting more wear on the lower number
82 SectorDescriptor* sector = last_new_;
84 // Look for a sector to use with enough space. The search uses a 3 priority
87 // Tier 1 is sector that already has valid data. During GC only select a
88 // sector that has no reclaimable bytes. Immediately use the first matching
89 // sector that is found.
91 // Tier 2 is find sectors that are empty/erased. While scanning for a partial
92 // sector, keep track of the first empty sector and if a second empty sector
93 // was seen. If during GC then count the second empty sector as always seen.
95 // Tier 3 is during garbage collection, find sectors with enough space that
96 // are not empty but have recoverable bytes. Pick the sector with the least
97 // recoverable bytes to minimize the likelyhood of this sector needing to be
98 // garbage collected soon.
99 for (size_t j = 0; j < descriptors_.size(); j++) {
101 if (sector == descriptors_.end()) {
102 sector = descriptors_.begin();
105 // Skip sectors in the skip list.
106 if (Contains(std::span(temp_sectors_to_skip_, sectors_to_skip), sector)) {
110 if (!sector->Empty(sector_size_bytes) && sector->HasSpace(size)) {
111 if ((find_mode == kAppendEntry) ||
112 (sector->RecoverableBytes(sector_size_bytes) == 0)) {
113 *found_sector = sector;
116 if ((non_empty_least_reclaimable_sector == nullptr) ||
117 (non_empty_least_reclaimable_sector->RecoverableBytes(
119 sector->RecoverableBytes(sector_size_bytes))) {
120 non_empty_least_reclaimable_sector = sector;
125 if (sector->Empty(sector_size_bytes)) {
126 if (first_empty_sector == nullptr) {
127 first_empty_sector = sector;
129 at_least_two_empty_sectors = true;
134 // Tier 2 check: If the scan for a partial sector does not find a suitable
135 // sector, use the first empty sector that was found. Normally it is required
136 // to keep 1 empty sector after the sector found here, but that rule does not
138 if (first_empty_sector != nullptr && at_least_two_empty_sectors) {
139 DBG(" Found a usable empty sector; returning the first found (%u)",
140 Index(first_empty_sector));
141 last_new_ = first_empty_sector;
142 *found_sector = first_empty_sector;
146 // Tier 3 check: If we got this far, use the sector with least recoverable
148 if (non_empty_least_reclaimable_sector != nullptr) {
149 *found_sector = non_empty_least_reclaimable_sector;
150 DBG(" Found a usable sector %u, with %u B recoverable, in GC",
151 Index(*found_sector),
152 unsigned((*found_sector)->RecoverableBytes(sector_size_bytes)));
156 // No sector was found.
157 DBG(" Unable to find a usable sector");
158 *found_sector = nullptr;
159 return Status::ResourceExhausted();
162 SectorDescriptor& Sectors::WearLeveledSectorFromIndex(size_t idx) const {
163 return descriptors_[(Index(last_new_) + 1 + idx) % descriptors_.size()];
166 // TODO: Consider breaking this function into smaller sub-chunks.
167 SectorDescriptor* Sectors::FindSectorToGarbageCollect(
168 std::span<const Address> reserved_addresses) const {
169 const size_t sector_size_bytes = partition_.sector_size_bytes();
170 SectorDescriptor* sector_candidate = nullptr;
171 size_t candidate_bytes = 0;
173 // Build a vector of sectors to avoid.
174 for (size_t i = 0; i < reserved_addresses.size(); ++i) {
175 temp_sectors_to_skip_[i] = &FromAddress(reserved_addresses[i]);
176 DBG(" Skip sector %u", Index(reserved_addresses[i]));
178 const std::span sectors_to_skip(temp_sectors_to_skip_,
179 reserved_addresses.size());
181 // Step 1: Try to find a sectors with stale keys and no valid keys (no
182 // relocation needed). Use the first such sector found, as that will help the
183 // KVS "rotate" around the partition. Initially this would select the sector
184 // with the most reclaimable space, but that can cause GC sector selection to
185 // "ping-pong" between two sectors when updating large keys.
186 for (size_t i = 0; i < descriptors_.size(); ++i) {
187 SectorDescriptor& sector = WearLeveledSectorFromIndex(i);
188 if ((sector.valid_bytes() == 0) &&
189 (sector.RecoverableBytes(sector_size_bytes) > 0) &&
190 !Contains(sectors_to_skip, §or)) {
191 sector_candidate = §or;
196 // Step 2: If step 1 yields no sectors, just find the sector with the most
197 // reclaimable bytes but no addresses to avoid.
198 if (sector_candidate == nullptr) {
199 for (size_t i = 0; i < descriptors_.size(); ++i) {
200 SectorDescriptor& sector = WearLeveledSectorFromIndex(i);
201 if ((sector.RecoverableBytes(sector_size_bytes) > candidate_bytes) &&
202 !Contains(sectors_to_skip, §or)) {
203 sector_candidate = §or;
204 candidate_bytes = sector.RecoverableBytes(sector_size_bytes);
209 // Step 3: If no sectors with reclaimable bytes, select the sector with the
210 // most free bytes. This at least will allow entries of existing keys to get
211 // spread to other sectors, including sectors that already have copies of the
212 // current key being written.
213 if (sector_candidate == nullptr) {
214 for (size_t i = 0; i < descriptors_.size(); ++i) {
215 SectorDescriptor& sector = WearLeveledSectorFromIndex(i);
216 if ((sector.valid_bytes() > candidate_bytes) &&
217 !Contains(sectors_to_skip, §or)) {
218 sector_candidate = §or;
219 candidate_bytes = sector.valid_bytes();
220 DBG(" Doing GC on sector with no reclaimable bytes!");
225 if (sector_candidate != nullptr) {
226 DBG("Found sector %u to Garbage Collect, %u recoverable bytes",
227 Index(sector_candidate),
228 unsigned(sector_candidate->RecoverableBytes(sector_size_bytes)));
230 DBG("Unable to find sector to garbage collect!");
232 return sector_candidate;
235 } // namespace pw::kvs::internal