Author Mark.Shannon
Recipients Mark.Shannon, carljm, corona10, dino.viehland, eelizondo, gregory.p.smith, nascheme, pablogsal, pitrou, shihai1991, steve.dower, tim.peters, vstinner
Date 2020-04-16.12:15:10
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Message-id <1587039311.36.0.0615666056862.issue40255@roundup.psfhosted.org>
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A big -1 to this.

You are asking the whole world to take a hit on both performance and memory use, in order to save Instagram memory.

The PR uses the term "immortal" everywhere. There is only one reference to copy-on-write in a comment. Yet this issue about making object headers immutable.
Immortality and object header immutability are not the same.

If object header immutability is to be a requirement, that needs a PEP.

If it is not requirement, but immortality is, then make the obvious improvement of changing the branchy code

if (!(obj->refcnt & IMMORTAL_BIT)) {
   obj->refcnt++;
}

to the branchless

obj->refcnt += ((obj->refcnt &IMMORTAL_BIT) != 0)

Immortality has advantages because it allows saturating reference counting and thus smaller object headers, but it is not the same as making the object header immutable.
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Date User Action Args
2020-04-16 12:15:11Mark.Shannonsetrecipients: + Mark.Shannon, tim.peters, nascheme, gregory.p.smith, pitrou, vstinner, carljm, dino.viehland, steve.dower, corona10, pablogsal, eelizondo, shihai1991
2020-04-16 12:15:11Mark.Shannonsetmessageid: <1587039311.36.0.0615666056862.issue40255@roundup.psfhosted.org>
2020-04-16 12:15:11Mark.Shannonlinkissue40255 messages
2020-04-16 12:15:10Mark.Shannoncreate