Mercurial > hg
view mercurial/mpatch.c @ 42043:1fac9b931d46
compression: introduce a `storage.revlog.zlib.level` configuration
This option control the zlib compression level used when compression revlog
chunk.
This is also a good excuse to pave the way for a similar configuration option
for the zstd compression engine. Having a dedicated option for each compression
algorithm is useful because they don't support the same range of values.
Using a higher zlib compression impact CPU consumption at compression time, but
does not directly affected decompression time. However dealing with small
compressed chunk can directly help decompression and indirectly help other
revlog logic.
I ran some basic test on repositories using different level. I am using the
mercurial, pypy, netbeans and mozilla-central clone from our benchmark suite.
All tested repository use sparse-revlog and got all their delta recomputed.
The different compression level has a small effect on the repository size
(about 10% variation in the total range). My quick analysis is that revlog
mostly store small delta, that are not affected by the compression level much.
So the variation probably mostly comes from better compression of the snapshots
revisions, and snapshot revision only represent a small portion of the
repository content.
I also made some basic timings measurements. The "read" timings are gathered using
simple run of `hg perfrevlogrevisions`, the "write" timings using `hg
perfrevlogwrite` (restricted to the last 5000 revisions for netbeans and
mozilla central). The timings are gathered on a generic machine, (not one of
our performance locked machine), so small variation might not be meaningful.
However large trend remains relevant.
Keep in mind that these numbers are not pure compression/decompression time.
They also involve the full revlog logic. In particular the difference in chunk
size has an impact on the delta chain structure, affecting performance when
writing or reading them.
On read/write performance, the compression level has a bigger impact.
Counter-intuitively, the higher compression levels improve "write" performance
for the large repositories in our tested setting. Maybe because the last 5000
delta chain end up having a very different shape in this specific spot? Or maybe
because of a more general trend of better delta chains thanks to the smaller
chunk and snapshot.
This series does not intend to change the default compression level. However,
these result call for a deeper analysis of this performance difference in the
future.
Full data
=========
repo level .hg/store size 00manifest.d read write
----------------------------------------------------------------
mercurial 1 49,402,813 5,963,475 0.170159 53.250304
mercurial 6 47,197,397 5,875,730 0.182820 56.264320
mercurial 9 47,121,596 5,849,781 0.189219 56.293612
pypy 1 370,830,572 28,462,425 2.679217 460.721984
pypy 6 340,112,317 27,648,747 2.768691 467.537158
pypy 9 338,360,736 27,639,003 2.763495 476.589918
netbeans 1 1,281,847,810 165,495,457 122.477027 520.560316
netbeans 6 1,205,284,353 159,161,207 139.876147 715.930400
netbeans 9 1,197,135,671 155,034,586 141.620281 678.297064
mozilla 1 2,775,497,186 298,527,987 147.867662 751.263721
mozilla 6 2,596,856,420 286,597,671 170.572118 987.056093
mozilla 9 2,587,542,494 287,018,264 163.622338 739.803002
author | Pierre-Yves David <pierre-yves.david@octobus.net> |
---|---|
date | Wed, 27 Mar 2019 18:35:27 +0100 |
parents | 763b45bc4483 |
children | d4ba4d51f85f |
line wrap: on
line source
/* mpatch.c - efficient binary patching for Mercurial This implements a patch algorithm that's O(m + nlog n) where m is the size of the output and n is the number of patches. Given a list of binary patches, it unpacks each into a hunk list, then combines the hunk lists with a treewise recursion to form a single hunk list. This hunk list is then applied to the original text. The text (or binary) fragments are copied directly from their source Python objects into a preallocated output string to avoid the allocation of intermediate Python objects. Working memory is about 2x the total number of hunks. Copyright 2005, 2006 Matt Mackall <mpm@selenic.com> This software may be used and distributed according to the terms of the GNU General Public License, incorporated herein by reference. */ #include <limits.h> #include <stdlib.h> #include <string.h> #include "bitmanipulation.h" #include "compat.h" #include "mpatch.h" /* VC9 doesn't include bool and lacks stdbool.h based on cext/util.h */ #if defined(_MSC_VER) || __STDC_VERSION__ < 199901L #define true 1 #define false 0 typedef unsigned char bool; #else #include <stdbool.h> #endif static struct mpatch_flist *lalloc(ssize_t size) { struct mpatch_flist *a = NULL; if (size < 1) { size = 1; } a = (struct mpatch_flist *)malloc(sizeof(struct mpatch_flist)); if (a) { a->base = (struct mpatch_frag *)malloc( sizeof(struct mpatch_frag) * size); if (a->base) { a->head = a->tail = a->base; return a; } free(a); } return NULL; } void mpatch_lfree(struct mpatch_flist *a) { if (a) { free(a->base); free(a); } } static ssize_t lsize(struct mpatch_flist *a) { return a->tail - a->head; } /* add helper to add src and *dest iff it won't overflow */ static inline bool safeadd(int src, int *dest) { if ((src > 0) == (*dest > 0)) { if (*dest > 0) { if (src > (INT_MAX - *dest)) { return false; } } else { if (src < (INT_MIN - *dest)) { return false; } } } *dest += src; return true; } /* subtract src from dest and store result in dest */ static inline bool safesub(int src, int *dest) { if (((src > 0) && (*dest < INT_MIN + src)) || ((src < 0) && (*dest > INT_MAX + src))) { return false; } *dest -= src; return true; } /* move hunks in source that are less cut to dest, compensating for changes in offset. the last hunk may be split if necessary. */ static int gather(struct mpatch_flist *dest, struct mpatch_flist *src, int cut, int offset) { struct mpatch_frag *d = dest->tail, *s = src->head; int postend, c, l; while (s != src->tail) { int soffset = s->start; if (!safeadd(offset, &soffset)) { break; /* add would overflow, oh well */ } if (soffset >= cut) { break; /* we've gone far enough */ } postend = offset; if (!safeadd(s->start, &postend) || !safeadd(s->len, &postend)) { break; } if (postend <= cut) { /* save this hunk */ int tmp = s->start; if (!safesub(s->end, &tmp)) { break; } if (!safeadd(s->len, &tmp)) { break; } if (!safeadd(tmp, &offset)) { break; /* add would overflow, oh well */ } *d++ = *s++; } else { /* break up this hunk */ c = cut; if (!safesub(offset, &c)) { break; } if (s->end < c) { c = s->end; } l = cut - offset - s->start; if (s->len < l) { l = s->len; } offset += s->start + l - c; d->start = s->start; d->end = c; d->len = l; d->data = s->data; d++; s->start = c; s->len = s->len - l; s->data = s->data + l; break; } } dest->tail = d; src->head = s; return offset; } /* like gather, but with no output list */ static int discard(struct mpatch_flist *src, int cut, int offset) { struct mpatch_frag *s = src->head; int postend, c, l; while (s != src->tail) { int cmpcut = s->start; if (!safeadd(offset, &cmpcut)) { break; } if (cmpcut >= cut) { break; } postend = offset; if (!safeadd(s->start, &postend)) { break; } if (!safeadd(s->len, &postend)) { break; } if (postend <= cut) { /* do the subtraction first to avoid UB integer overflow */ int tmp = s->start; if (!safesub(s->end, &tmp)) { break; } if (!safeadd(s->len, &tmp)) { break; } if (!safeadd(tmp, &offset)) { break; } s++; } else { c = cut; if (!safesub(offset, &c)) { break; } if (s->end < c) { c = s->end; } l = cut - offset - s->start; if (s->len < l) { l = s->len; } offset += s->start + l - c; s->start = c; s->len = s->len - l; s->data = s->data + l; break; } } src->head = s; return offset; } /* combine hunk lists a and b, while adjusting b for offset changes in a/ this deletes a and b and returns the resultant list. */ static struct mpatch_flist *combine(struct mpatch_flist *a, struct mpatch_flist *b) { struct mpatch_flist *c = NULL; struct mpatch_frag *bh, *ct; int offset = 0, post; if (a && b) { c = lalloc((lsize(a) + lsize(b)) * 2); } if (c) { for (bh = b->head; bh != b->tail; bh++) { /* save old hunks */ offset = gather(c, a, bh->start, offset); /* discard replaced hunks */ post = discard(a, bh->end, offset); /* insert new hunk */ ct = c->tail; ct->start = bh->start; ct->end = bh->end; if (!safesub(offset, &(ct->start)) || !safesub(post, &(ct->end))) { /* It was already possible to exit * this function with a return value * of NULL before the safesub()s were * added, so this should be fine. */ mpatch_lfree(c); c = NULL; goto done; } ct->len = bh->len; ct->data = bh->data; c->tail++; offset = post; } /* hold on to tail from a */ memcpy(c->tail, a->head, sizeof(struct mpatch_frag) * lsize(a)); c->tail += lsize(a); } done: mpatch_lfree(a); mpatch_lfree(b); return c; } /* decode a binary patch into a hunk list */ int mpatch_decode(const char *bin, ssize_t len, struct mpatch_flist **res) { struct mpatch_flist *l; struct mpatch_frag *lt; int pos = 0; /* assume worst case size, we won't have many of these lists */ l = lalloc(len / 12 + 1); if (!l) { return MPATCH_ERR_NO_MEM; } lt = l->tail; /* We check against len-11 to ensure we have at least 12 bytes left in the patch so we can read our three be32s out of it. */ while (pos >= 0 && pos < (len - 11)) { lt->start = getbe32(bin + pos); lt->end = getbe32(bin + pos + 4); lt->len = getbe32(bin + pos + 8); if (lt->start < 0 || lt->start > lt->end || lt->len < 0) { break; /* sanity check */ } if (!safeadd(12, &pos)) { break; } lt->data = bin + pos; if (!safeadd(lt->len, &pos)) { break; } lt++; } if (pos != len) { mpatch_lfree(l); return MPATCH_ERR_CANNOT_BE_DECODED; } l->tail = lt; *res = l; return 0; } /* calculate the size of resultant text */ ssize_t mpatch_calcsize(ssize_t len, struct mpatch_flist *l) { ssize_t outlen = 0, last = 0; struct mpatch_frag *f = l->head; while (f != l->tail) { if (f->start < last || f->end > len) { return MPATCH_ERR_INVALID_PATCH; } outlen += f->start - last; last = f->end; outlen += f->len; f++; } outlen += len - last; return outlen; } int mpatch_apply(char *buf, const char *orig, ssize_t len, struct mpatch_flist *l) { struct mpatch_frag *f = l->head; int last = 0; char *p = buf; while (f != l->tail) { if (f->start < last || f->start > len || f->end > len || last < 0) { return MPATCH_ERR_INVALID_PATCH; } memcpy(p, orig + last, f->start - last); p += f->start - last; memcpy(p, f->data, f->len); last = f->end; p += f->len; f++; } if (last < 0) { return MPATCH_ERR_INVALID_PATCH; } memcpy(p, orig + last, len - last); return 0; } /* recursively generate a patch of all bins between start and end */ struct mpatch_flist * mpatch_fold(void *bins, struct mpatch_flist *(*get_next_item)(void *, ssize_t), ssize_t start, ssize_t end) { ssize_t len; if (start + 1 == end) { /* trivial case, output a decoded list */ return get_next_item(bins, start); } /* divide and conquer, memory management is elsewhere */ len = (end - start) / 2; return combine(mpatch_fold(bins, get_next_item, start, start + len), mpatch_fold(bins, get_next_item, start + len, end)); }