Gentoo Archives: gentoo-amd64

From: Volker Armin Hemmann <volkerarmin@××××××××××.com>
To: gentoo-amd64@l.g.o
Subject: Re: [gentoo-amd64] Re: Memory usage; 32 bit vs 64 bit.
Date: Tue, 04 Jan 2011 13:02:49
Message-Id: 4d2319aa.0297df0a.5980.ffff91bf@mx.google.com
In Reply to: [gentoo-amd64] Re: Memory usage; 32 bit vs 64 bit. by Duncan <1i5t5.duncan@cox.net>
1 On Tuesday 04 January 2011 09:12:17 Duncan wrote:
2 > Volker Armin Hemmann posted on Tue, 04 Jan 2011 08:27:28 +0100 as
3 >
4 > excerpted:
5 > > swap kills interactivity and is really, really bad on linux. No matter
6 > > how much you stripe it. Swap is a true horror. So setting swappiness to
7 > > 100 (which means: keep caches alive, no matter what and swap the hell
8 > > out of it) is a really bad idea. In my experience it is better to have a
9 > > very low swappiness and let the kernel get the occasional data from
10 > > disk, than to swap to the same disks. Strange eh?
11 > >
12 > > But better to wait 1.5s longer for konqueror to display a directory than
13 > > to have a jerky mouse and input lag because of swap. Remember: the
14 > > kernel ALWAYS swaps out the wrong stuff.
15 > > I have swappiness at 60 - and back in the 4GB days at 0. Because swap
16 > > sucks so much.
17 > >
18 > > You are not required to believe that. But just google.
19 >
20 > All I can go on is my experience, which agrees with you (and most of the
21 > advice on the net) when it's a single-core CPU on single-spindle storage,
22 > but I've found the experience rather different on multi-core machines
23 > driving quad-spindle striped swap on mirrored RAID, with enough memory
24 > swap usage is trivial in the ordinary case. Once swap usage hits half a
25 > gig or so, yes, it's noticed, but until then, I literally don't normally
26 > notice it unless/until I happen to see the usage reported on the system
27 > monitors.
28 >
29 > OTOH, losing portage tree cache or news (nntp) article cache and having to
30 > fetch the data from disk can be quite noticeable, as it DEFINITELY is the
31 > first time I access after a reboot (the infamous cold-cache case), the
32 > biggest reason I tend to leave the system running for weeks at a time,
33 > rebooting only to load a new test kernel or the like.
34 >
35 > (FWIW, I use app-admin/lib_users to track programs using stale/already-
36 > deleted libs after an update, and after quitting kde/X, restart daemons,
37 > etc, to clear the list if necessary, thus clearing that source of both
38 > security vulns and so-called anon-memory usage. I do use the
39 > portage-2.2.0_alphas with preserve-libs, but use FEATURES=-preserve-libs
40 > to avoid that source of bugs, so the old libs do normally get deleted.)
41
42 well, I don't waste electricity. I do have / on a ssd and /var with portage on
43 a raifd5. And waiting a few seconds longer for emerge -auvDtn world to give
44 results does not matter for me.
45
46 But a stuck keyboard because of swapping? (swap striped to three disks, 4core
47 processor) Inacceptable.
48
49 And so swappiness has to stay down. Many days I don't even turn swap on.
50 Seeing gcc oom is much less annoying than swap.
51
52 It got better over the years but it is still far from being acceptable.