8000 bpo-37029: keep usable_arenas in sorted order without searching by tim-one · Pull Request #13612 · python/cpython · GitHub
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bpo-37029: keep usable_arenas in sorted order without searching #13612

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Merged
merged 5 commits into from
Jun 1, 2019
Merged

bpo-37029: keep usable_arenas in sorted order without searching #13612

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c691a69
Issue 37029: first stab at removing all searching to keep usable_arenas
tim-one May 28, 2019
f4a60e8
📜🤖 Added by blurb_it.
blurb-it[bot] May 28, 2019
efe1e63
Beefed up an assert; added the BPO number to a comment.
tim-one May 28, 2019
0b36d42
Merge branch 'remove-arena-search' of https://github.com/tim-one/cpyt…
tim-one May 28, 2019
0463a7d
And added one more assert.
tim-one May 28, 2019
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Beefed up an assert; added the BPO number to a comment.
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@tim-one
tim-one committed May 28, 2019
commit efe1e63d18f112d8ebd8cc8df08e255fcd2d8bb8
9 changes: 7 additions & 2 deletions Objects/obmalloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1166,7 +1166,7 @@ used to be done by one-at-a-time linear search when an arena's number of
free pools changed. That could, overall, consume time quadratic in the
number of arenas. That didn't really matter when there were only a few
hundred arenas (typical!), but could be a timing disaster when there were
hundreds of thousands. See PR FIXME.
hundreds of thousands. See bpo-37029.

Now we have a vector of "search fingers" to eliminate the need to search:
nfp2lasta[nfp] returns the last ("rightmost") arena in usable_arenas
Expand Down Expand Up @@ -1742,7 +1742,12 @@ pymalloc_free(void *ctx, void *p)
* are no arenas in usable_arenas with that value.
*/
struct arena_object* lastnf = nfp2lasta[nf];
assert(nf == 0 || lastnf != NULL);
assert((nf == 0 && lastnf == NULL) ||
(nf > 0 &&
lastnf != NULL &&
lastnf->nfreepools == nf &&
(lastnf->nextarena == NULL ||
nf < lastnf->nextarena->nfreepools)));
if (lastnf == ao) { /* it is the rightmost */
struct arena_object* p = ao->prevarena;
nfp2lasta[nf] = (p != NULL && p->nfreepools == nf) ? p : NULL;
Expand Down
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