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unposted: reformulate 32285 to lift the fheap->sp test out of the loop, improve commentary

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Barton E. Schaefer 2014-01-22 21:47:29 -08:00
parent 3e06aeabd8
commit 6c603a4127
2 changed files with 14 additions and 15 deletions
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5
ChangeLog
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@ -1,3 +1,8 @@
2014-01-22 Barton E. Schaefer <schaefer@zsh.org>
* unposted: Src/mem.c: reformulate 32285 to lift the fheap->sp
test out of the loop, improve commentary
2014-01-19 Barton E. Schaefer <schaefer@zsh.org>
* 32294 (plus typo fix): Src/utils.c: prevent buffer overflow when

24
Src/mem.c
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@ -319,23 +319,26 @@ freeheap(void)
h_free++;
#endif
/* At this point we used to do:
fheap = NULL;
*
/*
* When pushheap() is called, it sweeps over the entire heaps list of
* arenas and marks every one of them with the amount of free space in
* that arena at that moment. zhalloc() is then allowed to grab bits
* out of any of those arenas that have free space.
*
* With the above reset of fheap, the loop below sweeps back over the
* Whenever fheap is NULL here, the loop below sweeps back over the
* entire heap list again, resetting the free space in every arena to
* the amount stashed by pushheap() and finding the first arena with
* free space to optimize zhalloc()'s next search. When there's a lot
* of stuff already on the heap, this is an enormous amount of work,
* and performance goes to hell.
*
* However, there doesn't seem to be any reason to reset fheap before
* beginning this loop. Either it's already correct, or it has never
* However, if the arena to which fheap points is unused, we want to
* free it, so we have no choice but to do the sweep for a new fheap.
*/
if (fheap && !fheap->sp)
fheap = NULL; /* We used to do this unconditionally */
/*
* In other cases, either fheap is already correct, or it has never
* been set and this loop will do it, or it'll be reset from scratch
* on the next popheap(). So all that's needed here is to pick up
* the scan wherever the last pass [or the last popheap()] left off.
@ -367,15 +370,6 @@ freeheap(void)
}
#endif
} else {
if (h == fheap && h != heaps) {
/*
* When deallocating the last arena with free space,
* loop back through the list to find another one.
*/
fheap = NULL;
hn = heaps;
continue;
}
#ifdef USE_MMAP
munmap((void *) h, h->size);
#else