From: Dmitrii Korobeinikov <dim1212k@gmail.com>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: emacs-devel <emacs-devel@gnu.org>
Subject: Re: Garbage collector: is 800kb a good default?
Date: Thu, 9 Apr 2020 20:20:20 +0600 [thread overview]
Message-ID: <CA+Yh0SSjLGDRNscdJM64Q=u4ZgNenzZSWYMVnhZojp+xpP_PYw@mail.gmail.com> (raw)
In-Reply-To: <jwvh7xs4wtt.fsf-monnier+emacs@gnu.org>
> Running GC frequently is done largely to try and keep total heap size
> and memory fragmentation under control. So completely refraining from
> running GC while non-idle is probably not a great solution, but I do
> agree that adding a "GC when idle" would not only be great in itself but
> would also let us increase the default thresholds somewhat. Tho I don't
> think we can increase the threshold as much as you suggest without
> having significant detrimental effects.
So, are there any stats on how much worse the fragmentation gets w/
higher thresholds and how much it effects emacs as a result? (By the
way, I am not really suggesting 80MB, just testing it out at the
moment : ) )
> 2- 38% is pretty high
Just for the reference, I've seen the value of 25 in one of the
threads nearby [1], not sure why mine is so high.
Best,
DK
[1] https://lists.gnu.org/archive/html/emacs-devel/2020-04/msg00406.html
чт, 9 апр. 2020 г. в 19:47, Stefan Monnier <monnier@iro.umontreal.ca>:
>
> > Of course, raising the threshold significantly higher on its own is
> > not a very good idea. But if paired with an idle timer like suggested
> > here [2], then it all starts looking like a decent combination:
>
> I agree that it's worth investigating improvements based on dynamically
> changing the GC threshold. What you're pointing out is that from the
> user's point of view, a GC during idle time is free (so it can occur
> frequently) and also that a GC during non-idle time can delay redisplay,
> so (ignoring all other impacts of GC) we should refrain from running GC
> while non-idle and trigger GC everything we're idle.
>
> Running GC frequently is done largely to try and keep total heap size
> and memory fragmentation under control. So completely refraining from
> running GC while non-idle is probably not a great solution, but I do
> agree that adding a "GC when idle" would not only be great in itself but
> would also let us increase the default thresholds somewhat. Tho I don't
> think we can increase the threshold as much as you suggest without
> having significant detrimental effects.
>
> There 2 additional ways to attack the problem, BTW:
>
> 1- replace our GC with a concurrent GC. This would let us move those
> 38% GC overheard to one of the other CPU cores sitting idle while the
> only CPU core running Emacs is frantically trying to scroll through
> your buffer (it would also slow down both the GC and the main thread
> a bit, but in the current context of plentiful CPU cores it would
> still be very worthwhile).
> [ Along the same lines, making our GC parallel could cut those 38%
> down to some extent, as would a generational GC. ]
>
> 2- 38% is pretty high. Usually this indicates that the GC is not
> efficient: it works hard yet reclaims very little memory likely
> because the application is allocating a lot of objects which are
> *not* temporary. This is also the typical situation during Emacs's
> startup where we're loading packages and initializing big
> data-structures, so after allocating our GC-threshold of data the GC
> is run but doesn't collect much garbage because all that data is
> there to stay.
> We can't really know beforehand if a GC will reclaim a lot of memory,
> but we could "use the past to predict the future": we could set the
> threshold higher when the last GC reclaimed too little garbage.
>
> I had sent a tentative patch for the "GC when idle" feature but it had
> some rough edges, and some details of the GC code have changed since.
> I'd welcome a patch to do that. It shouldn't require many changes.
> Similarly, point (2) above should be fairly simple to add.
>
>
> Stefan
>
next prev parent reply other threads:[~2020-04-09 14:20 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-09 11:59 Garbage collector: is 800kb a good default? Dmitrii Korobeinikov
2020-04-09 12:33 ` Eli Zaretskii
2020-04-09 13:44 ` Dmitrii Korobeinikov
2020-04-09 14:02 ` Eli Zaretskii
2020-04-09 14:46 ` Dmitrii Korobeinikov
2020-04-09 16:42 ` Eli Zaretskii
2020-04-10 16:40 ` Dmitrii Korobeinikov
2020-04-09 19:05 ` Stefan Monnier
2020-04-10 16:26 ` Dmitrii Korobeinikov
2020-04-09 18:48 ` Stefan Monnier
2020-04-10 14:26 ` Bruno Félix Rezende Ribeiro
2020-04-10 16:49 ` Eli Zaretskii
2020-04-10 18:26 ` Bruno Félix Rezende Ribeiro
2020-04-10 18:53 ` Paul Eggert
2020-04-09 13:47 ` Stefan Monnier
2020-04-09 14:20 ` Dmitrii Korobeinikov [this message]
2020-04-09 14:23 ` Eli Zaretskii
2020-04-09 18:42 ` Stefan Monnier
2020-04-09 19:08 ` Eli Zaretskii
2020-04-09 19:31 ` Stefan Monnier
2020-04-10 6:19 ` Eli Zaretskii
2020-04-10 13:03 ` Stefan Monnier
2020-04-10 13:42 ` Eli Zaretskii
2020-04-10 14:34 ` Stefan Monnier
2020-04-10 14:38 ` Stefan Monnier
2020-04-10 15:37 ` Eli Zaretskii
2020-04-10 15:52 ` Andrea Corallo
2020-04-10 16:45 ` Stefan Monnier
2020-04-10 17:18 ` Andrea Corallo
2020-04-09 14:48 ` Andrea Corallo
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