From: Jamie Lokier <lk@tantalophile.demon.co.uk>
To: Linus Torvalds <torvalds@transmeta.com>,
"H. Peter Anvin" <hpa@zytor.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: /proc/<n>/maps getting _VERY_ long
Date: Mon, 6 Aug 2001 19:41:20 +0100 [thread overview]
Message-ID: <20010806194120.A5803@thefinal.cern.ch> (raw)
In-Reply-To: <20010805171202.A20716@weta.f00f.org> <20010805204143.A18899@alcove.wittsend.com> <9kkq9k$829$1@penguin.transmeta.com> <9kkr7r$mov$1@cesium.transmeta.com> <9kl6aa$87l$1@penguin.transmeta.com>
In-Reply-To: <9kl6aa$87l$1@penguin.transmeta.com>; from torvalds@transmeta.com on Mon, Aug 06, 2001 at 04:26:50AM +0000
Linus Torvalds wrote:
> >Do you count applications which selectively mprotect()'s memory (to
> >trap SIGSEGV and maintain coherency with on-disk data structures) as
> >"broken applications"?
> >
> >Such applications *can* use large amounts of mprotect()'s.
>
> Note that such applications tend to not get any advantage from merging -
> it does in fact only slow things down (because then the next mprotect
> just has to split the thing again).
>
> No, they aren't broken, but they should know that the use of lots of
> small memory segments (even if it is a design goal) can and will slow
> down page faulting, and use more memory for MM management for example.
>
> Linux does have a log(n) vma lookup, so the slowdown isn't huge.
There are garbage collectors that use mprotect() and SEGV trapping per
page. It would be nice if there was a way to change the protections per
page without requiring a VMA for each one.
Btw, Linux has pretty fast SIGSEGV handling (the fastest of any
OS/machine combination that I measured), so it's a good platform for
this sort of thing. I measured 7.75 microseconds per page for SEGV
trapping followed by mprotect() in the handler, on a particular test on
a 600MHz Pentium III.
-- Jamie
next prev parent reply other threads:[~2001-08-10 21:31 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-08-04 15:43 /proc/<n>/maps getting _VERY_ long Chris Wedgwood
2001-08-05 2:17 ` Rik van Riel
2001-08-05 5:12 ` Chris Wedgwood
2001-08-05 13:06 ` Alan Cox
2001-08-05 13:18 ` Chris Wedgwood
2001-08-05 23:07 ` Jakob Østergaard
2001-08-05 23:41 ` Linus Torvalds
2001-08-06 0:41 ` Michael H. Warfield
2001-08-06 1:01 ` Linus Torvalds
2001-08-06 1:17 ` H. Peter Anvin
2001-08-06 4:26 ` Linus Torvalds
2001-08-06 6:30 ` H. Peter Anvin
2001-08-06 18:41 ` Jamie Lokier [this message]
2001-08-10 21:55 ` Linus Torvalds
2001-08-10 22:00 ` H. Peter Anvin
2001-08-10 23:03 ` Nicolas Pitre
2001-08-10 23:26 ` Linus Torvalds
2001-08-10 23:55 ` Rik van Riel
2001-08-11 1:04 ` Pavel Machek
2001-08-06 11:52 ` Alan Cox
2001-08-06 12:23 ` Chris Wedgwood
2001-08-06 13:17 ` Alan Cox
2001-08-06 13:55 ` Chris Wedgwood
2001-08-06 9:43 ` [LONGish] Brief analysis of VMAs (was: /proc/<n>/maps getting _VERY_ long) Chris Wedgwood
2001-08-05 6:44 /proc/<n>/maps getting _VERY_ long David Luyer
2001-08-05 7:21 ` Anders Eriksson
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