Subject: Re: Performance Problem: malloc() is calling madvise()
To: Simon Burge <email@example.com>
From: Jason R Thorpe <firstname.lastname@example.org>
Date: 05/19/2000 07:44:51
On Fri, May 19, 2000 at 09:38:46PM +1000, Simon Burge wrote:
> The man page for malloc() talks more about this. Hmm, it also says the
> calls to madvise() are off by default! FreeBSD changed the default
> from on to off at some stage - we grabbed their code before the change
> and their manpage after it. They changed it because "Recent VM system
> changes have made this too expensive." - our madvise() manpage says that
> until NetBSD 1.5 (ie in -current between 1.4 and 1.5), madvise() did
> nothing. Anyone object to me changing the default to match the manpage
> and what FreeBSD currently does?
Yes, we should probably change malloc(3) to default to "no MADV_FREE by
default", although it would be nice if malloc() were a little smarter
about it and gave the advice when there was some threshold of pages free.
Looks like what it does it just always give the advice every time a
page is put on the free list. That's sort of silly in e.g. the C++
case, as you're going to get a big ping-pong effect.
-- Jason R. Thorpe <email@example.com>