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https://github.com/littlefs-project/littlefs.git
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Limit crystal_thresh to >=prog_size
I confused myself a bit while benchmarking because crystal_thresh <
prog_size was showing some very confusing results. But it turns out the
relevant code was just not written well enough to support this
configuration.
And, to be fair, this configuration really doesn't make sense. The whole
point of the fragment + crystallization system is so we never have to
write unaligned data to blocks. I mean, we could explicitly write
padding in this case, but why?
---
This should probably eventually be either an assert or mutable limit,
but in the meantime I'm just adjusting crystal_thresh at runtime, which
adds a bit of code:
code stack ctx
before: 37076 2352 684
after: 37112 (+0.1%) 2352 (+0.0%) 684 (+0.0%)
On the plus side, this prevents crystal_thresh=0 issues much more
elegantly.
This commit is contained in:
Christopher Haster
57
lfs3.c
57
lfs3.c
@ -12727,7 +12727,9 @@ int lfs3_file_opencfg_(lfs3_t *lfs3, lfs3_file_t *file,
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if (lfs3_o_iswrset(file->b.h.flags)
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&& file->cache.size <= lfs3->cfg->inline_size
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&& file->cache.size <= lfs3->cfg->fragment_size
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&& file->cache.size < lfs3_max(lfs3->cfg->crystal_thresh, 1)) {
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&& file->cache.size < lfs3_max(
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lfs3->cfg->crystal_thresh,
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lfs3->cfg->prog_size)) {
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// we need to mark as unsync for sync to do anything
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file->b.h.flags |= LFS3_o_UNSYNC;
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@ -13270,7 +13272,9 @@ static int lfs3_file_graft_(lfs3_t *lfs3, lfs3_file_t *file,
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// carve bptr into fragment?
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|| (lfs3_bptr_size(&l) <= lfs3->cfg->fragment_size
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&& lfs3_bptr_size(&l)
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< lfs3_max(lfs3->cfg->crystal_thresh, 1))) {
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< lfs3_max(
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lfs3->cfg->crystal_thresh,
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lfs3->cfg->prog_size))) {
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rattrs[rattr_count++] = LFS3_RATTR_DATA(
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LFS3_TAG_GROW | LFS3_TAG_MASK8 | LFS3_TAG_DATA,
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-(bid+1 - pos),
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@ -13320,7 +13324,9 @@ static int lfs3_file_graft_(lfs3_t *lfs3, lfs3_file_t *file,
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// carve bptr into fragment?
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|| (lfs3_bptr_size(&r) <= lfs3->cfg->fragment_size
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&& lfs3_bptr_size(&r)
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< lfs3_max(lfs3->cfg->crystal_thresh, 1))) {
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< lfs3_max(
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lfs3->cfg->crystal_thresh,
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lfs3->cfg->prog_size))) {
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r_rattr_ = LFS3_RATTR_DATA(
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LFS3_TAG_DATA, bid+1 - (pos+weight),
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&r.d);
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@ -13757,7 +13763,9 @@ static int lfs3_file_flushset_(lfs3_t *lfs3, lfs3_file_t *file,
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// enough data for a block?
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#ifndef LFS3_2BONLY
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if (size >= lfs3->cfg->crystal_thresh) {
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if (size >= lfs3_max(
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lfs3->cfg->crystal_thresh,
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lfs3->cfg->prog_size)) {
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// align down for prog alignment
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lfs3_ssize_t d = lfs3_aligndown(
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lfs3_min(size, lfs3->cfg->block_size),
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@ -13873,7 +13881,9 @@ static int lfs3_file_flush_(lfs3_t *lfs3, lfs3_file_t *file,
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&& pos < block_start + lfs3->cfg->block_size
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// if we're more than a crystal away, graft and check crystal
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// heuristic before resuming
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&& pos - block_end < lfs3_max(lfs3->cfg->crystal_thresh, 1)
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&& pos - block_end < lfs3_max(
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lfs3->cfg->crystal_thresh,
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lfs3->cfg->prog_size)
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// need to bail if we can't meet prog alignment
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&& (pos + size) - block_end >= lfs3->cfg->prog_size) {
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// mark as uncrystallized to avoid allocating a new block
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@ -13924,9 +13934,13 @@ static int lfs3_file_flush_(lfs3_t *lfs3, lfs3_file_t *file,
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// if we haven't already exceeded our crystallization threshold,
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// find left crystal neighbor
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lfs3_off_t poke = lfs3_smax(
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crystal_start - (lfs3->cfg->crystal_thresh-1),
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crystal_start - (lfs3_max(
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lfs3->cfg->crystal_thresh,
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lfs3->cfg->prog_size)-1),
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0);
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if (crystal_end - crystal_start < lfs3->cfg->crystal_thresh
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if (crystal_end - crystal_start < lfs3_max(
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lfs3->cfg->crystal_thresh,
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lfs3->cfg->prog_size)
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&& crystal_start > 0
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&& poke < file->b.shrub.r.weight
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// don't bother looking up left after the first block
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@ -13960,9 +13974,13 @@ static int lfs3_file_flush_(lfs3_t *lfs3, lfs3_file_t *file,
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// if we haven't already exceeded our crystallization threshold,
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// find right crystal neighbor
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poke = lfs3_min(
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crystal_start + (lfs3->cfg->crystal_thresh-1),
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crystal_start + (lfs3_max(
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lfs3->cfg->crystal_thresh,
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lfs3->cfg->prog_size)-1),
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file->b.shrub.r.weight-1);
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if (crystal_end - crystal_start < lfs3->cfg->crystal_thresh
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if (crystal_end - crystal_start < lfs3_max(
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lfs3->cfg->crystal_thresh,
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lfs3->cfg->prog_size)
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&& crystal_end < file->b.shrub.r.weight) {
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lfs3_bid_t bid;
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lfs3_bid_t weight;
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@ -13994,9 +14012,12 @@ static int lfs3_file_flush_(lfs3_t *lfs3, lfs3_file_t *file,
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// write to the file
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// below our crystallization threshold? fallback to writing fragments
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if (crystal_end - crystal_start < lfs3->cfg->crystal_thresh
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// enough for prog alignment?
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|| crystal_end - crystal_start < lfs3->cfg->prog_size) {
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//
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// note as long as crystal_thresh >= prog_size, this also ensures we
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// have enough for prog alignment
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if (crystal_end - crystal_start < lfs3_max(
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lfs3->cfg->crystal_thresh,
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lfs3->cfg->prog_size)) {
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goto fragment;
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}
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@ -14744,7 +14765,9 @@ int lfs3_file_sync(lfs3_t *lfs3, lfs3_file_t *file) {
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if (file->cache.size == lfs3_file_size_(file)
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&& file->cache.size <= lfs3->cfg->inline_size
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&& file->cache.size <= lfs3->cfg->fragment_size
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&& file->cache.size < lfs3_max(lfs3->cfg->crystal_thresh, 1)) {
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&& file->cache.size < lfs3_max(
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lfs3->cfg->crystal_thresh,
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lfs3->cfg->prog_size)) {
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// discard any overwritten leaves, this also clears the
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// LFS3_o_UNCRYST and LFS3_o_UNGRAFT flags
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lfs3_file_discardleaf(file);
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@ -14970,7 +14993,9 @@ int lfs3_file_truncate(lfs3_t *lfs3, lfs3_file_t *file, lfs3_off_t size_) {
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if (!lfs3_bptr_isbptr(&file->leaf.bptr)
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|| (lfs3_bptr_size(&file->leaf.bptr) <= lfs3->cfg->fragment_size
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&& lfs3_bptr_size(&file->leaf.bptr)
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< lfs3_max(lfs3->cfg->crystal_thresh, 1))) {
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< lfs3_max(
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lfs3->cfg->crystal_thresh,
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lfs3->cfg->prog_size))) {
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lfs3_file_discardleaf(file);
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}
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@ -15063,7 +15088,9 @@ int lfs3_file_fruncate(lfs3_t *lfs3, lfs3_file_t *file, lfs3_off_t size_) {
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if (!lfs3_bptr_isbptr(&file->leaf.bptr)
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|| (lfs3_bptr_size(&file->leaf.bptr) <= lfs3->cfg->fragment_size
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&& lfs3_bptr_size(&file->leaf.bptr)
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< lfs3_max(lfs3->cfg->crystal_thresh, 1))) {
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< lfs3_max(
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lfs3->cfg->crystal_thresh,
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lfs3->cfg->prog_size))) {
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lfs3_file_discardleaf(file);
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}
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6
lfs3.h
6
lfs3.h
@ -573,9 +573,9 @@ struct lfs3_cfg {
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// values will crystallize more eagerly, reducing disk usage, but
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// increasing the cost of random-writes.
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//
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// 0 or 1 only writes blocks, minimizing disk usage, while -1 or any
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// value > block_size only writes fragments, minimizing random-write
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// cost.
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// 0 tries to only writes blocks, minimizing disk usage, while -1 or
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// any value > block_size only writes fragments, minimizing
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// random-write cost.
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#ifndef LFS3_RDONLY
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lfs3_size_t crystal_thresh;
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#endif
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