From: Daniel Berlin <dberlin@dberlin.org>
To: Zack Weinberg <zack@codesourcery.com>
Cc: Jeff Sturm <jsturm@one-point.com>, gcc@gcc.gnu.org
Subject: Re: Locality problems caused by size based allocation?
Date: Tue, 17 Dec 2002 21:01:00 -0000 [thread overview]
Message-ID: <DD0D98C8-122B-11D7-9564-000393575BCC@dberlin.org> (raw)
In-Reply-To: <87wum8i0zi.fsf@egil.codesourcery.com>
On Tuesday, December 17, 2002, at 08:12 PM, Zack Weinberg wrote:
> Daniel Berlin <dberlin@dberlin.org> writes:
>
>> On Tue, 17 Dec 2002, Jeff Sturm wrote:
>>> What exactly is "size based allocation"?
>> What ggc-page does, which is segregate objects based on size rather
>> than
>> age or object type.
>>
>> This doesn't work well for RTL, for instance, where you have 3 (or
>> was it
>> 2 or 4, i forget which) sizes of RTL, so size allocation guarantees
>> that
>> in a linear walk of RTL, you'll end up moving across all different
>> random pages.
>
> FYI, I plan to address this particular issue after the New Year, by
> picking up Dave Miller's suggestion from awhile back to avoid ever
> allocating long-lived RTL, and then reverting RTL to obstacks -- but
> just one obstack, data on which lives only during calls to expand_body
> (or something like that).
obstacks aren't something we should revert to.
Implement a pool/subpool system like APR has, or copy the region stuff
out of libbanshee/libcompat (it does subregions and whatnot. It's
actually part of a runtime system for a compiler based partly on gcc
that does safe regions, so it's rather well implemented). It will
compile without problems and without anything outside that directory
being needed (it has a name conflict in profile.[ch], but renaming
works fine)
Obstacks just don't have enough flexibility or promise that we should
go back to them.
It doesn't change the greater locality problem however.
I would think mark and sweep regions/pools (you can have subpools and
whatnot, for per iteration things) per pass, one for rtl, and one for
trees, would be a better idea.
>
> zw
next prev parent reply other threads:[~2002-12-18 1:56 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-12-16 11:19 Daniel Berlin
2002-12-17 15:47 ` Jeff Sturm
2002-12-17 16:13 ` Daniel Berlin
2002-12-17 20:03 ` Zack Weinberg
2002-12-17 21:01 ` Daniel Berlin [this message]
2002-12-17 23:16 ` Jeff Sturm
2002-12-18 0:41 ` Zack Weinberg
2002-12-18 12:59 ` Jeff Sturm
2002-12-18 5:44 ` Fergus Henderson
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