Peng posted <[EMAIL PROTECTED]>, excerpted below, on Sun, 26 Jun 2005 08:38:49 -0400:
>> When I get the memory upgrade I'm looking at, not rebooting from an X >> shutdown will likely become even MORE common. I'll /hate/ rebooting, >> because with 4, possibly 8 gig of memory (I'm tempted to go to the full >> 16, but it's too hard to zero out the CC again when the balance gets that >> high), and apps normally only taking a quarter to a half a gig (it looks >> like I'll occasionally run a full gig of app memory) most stuff will stay >> in that 3-7 gigs of cache once read from disk the first time, so virtually >> everything will be loaded from cache, not disk. Rebooting will of course >> mean losing that cache, having to start over reading everything from slow >> disk once again. That'll SUCK, likely enough that I'll be trying to avoid >> it, even more than I do now, when it's no big deal. I'm not an uptime >> freak, usually rebooting every few days (uptime of almost 5 days, now, >> that one was a shutdown to depower the breaker box so I could trade out >> the a/c breaker, as it was getting weak and tripping, not a good thing >> here in Phoenix, with temps running ~45 C, 113 F, last week, a much more >> reasonable 40 C this week, still 30 C, 86 F, @ 4 AM), but I can imagine >> getting to the point where I'll complain about rebooting, since I rebooted >> "only" a week or two ago. That'll be particularly likely with the new >> SMP-suspend that's probably going to be in 2.6.13. Definitely looking >> forward to that! > > Just curious, what do you do with that much RAM? Well, I've only a gig, currently. I have swap disabled and in fact the option toggled off in my kernel config so it's not even in the kernel, and have been running that way for probably a year, now. As mentioned, my applications (used memory minus cache and buffers) normally only take up a quarter to a third of that gig, seldom more than half. However, if I try scanning a full page at full scanner resolution, I run out of memory at about 90% scan completion. Also, I have a dual Opteron here, and /could/ probably go to 4 compile jobs for more efficiency during emerges, if I had more memory. Most emerges use only a small portion of that gig even at 4 concurrent jobs. However, some C++ compilation, I've noticed it mostly on KDE, gets pretty memory intensive, and I cut back to three jobs to prevent memory starvation there. That tells me I could use a gig and a half to two gigs at times for app memory. Of course, the vast majority of the time I'd be running less than half a gig, as I said, a quarter to a third gig, of actual app memory use, and the rest would be cache. That's really what the additional memory is for. Having a gig of memory, more than half of which is almost always disc cache, I've come to realize just how big the advantages of disc cache over having to read a file from disc are. I /dread/ that first emerge sync (which loads the portage tree into cache) and first emerge (the time at the end where it scans /etc/ and the other protected dirs for changed files that need to be etc-updated, which reads all those dirs into cache), after a reboot or task that used most of memory, because they always take so much /longer/ than what I'm used to, when all that stuff is already in cache and therefore scanned at the speed of memory, not the speed of the hard drive. So... that got me thinking... I routinely load a several hundred song playlist into noatun, totalling several gigs of media. A few hours of playing that, and guess what -- most of my current half to three quarter gig cache is going to be media files. Yet, I don't have enough memory to cache the entire playlist worth of files, so even so, if I had the disc on idle spin-down (I don't), it'd be spinning back up to load the next few songs, every so often. Meanwhile, that's cache that won't remember the portage tree or CONFIG_PROTECTed dirs, next time I sync and update. 8 gig of memory would just about cover all that. 12 would almost certainly do so, 16, 8 2-gig sticks, 4 sticks to each CPU/MMU, would do so with a decent amount of memory to spare. I could set the discs to spin-down on idle, and after the initial boot and load of my normal stuff, the discs would spin down and wouldn't need to spin back up again unless I loaded something else or for any changes that needed written back. Meanwhile, after that initial load, virtually everything I'd be using, including several gigs worth of music, the entire portage tree, all the apps and libs I normally use, and the entire trees of all CONFIG_PROTECTed dirs, would be in cache, available at the speed of memory retrieval, without having to wait on the disc. Unfortunately, two-gig memory sticks (DDR 400 PC3200), at least for the registered memory required for Opterons, are still above the price-point "knee". That is, a two-gig memory stick still costs more than twice (in fact, about three times) what a single-gig memory stick costs. At about $350/2-gig stick (pricewatch.com), I can't quite budget nor really justify paying $2800 to max out my memory to the full 16 gig. However, at about $105 (generic memory) to $122 (Micron memory, low end price, again pricewatch.com) for a gig stick, I CAN budget $500 for four gigs, and /could/ budget $1000 to fill up up the 8 slots with 8 gigs. Alternatively, I could cut out some other purchases for a bit longer and spend the $700 on two 2-gig sticks, or $1400 on four 2-gig sticks, leaving the rest for later after the price notches down a bit further. ... I'm also working on being a Gentoo amd64 AT (official Gentoo arch tester, no, I'm not there yet, but that's my near-term goal). With a dual Opteron, in fact bought with the idea of ultimately using some of the resources to contribute back to the FLOSS community, I could set portage's jobs to 1 or 2, possibly up the niceness a few notches, and with at /least/ 2 gigs and preferably 4 gigs of memory, I'd likely only notice it if I glanced at the CPU graphs -- system responsiveness for most tasks wouldn't be affected at all. Limited to the gig of memory I currently have, I wouldn't notice it /much/ (after all, I can do my normal emerges at 3 jobs as mentioned above and responsiveness is still decent), but I'd notice it some, if only because it would restrict my ability to do things like large scans at the same time. Therefore, I've set myself the personal goal of upgrading my memory about the same time I finish studying the Gentoo dev handbook and related documentation, and take my AT quiz, allowing me to take my community contributions to an entirely new level. Tying the two together like that makes sense both because of the resulting personal cross-motivation, and because of the additional work I'll be putting my system thru once that occurs, compiling, installing, and running all sorts of packages not because I'm really interested in using them, but because they need tested so bugs can be filed and fixed as necessary, and the packages ultimately keyworded ~amd64 and then amd64 (stable), making them available for use by others not quite so adventurous or having the resources and time to do their own package testing. ... What I'd /really/ like to see is the 2-gig sticks coming down to $300, where I'd feel comfortable buying 2-4 of them now. Barring that, I'd like to see non-generic 1-gig sticks at $100, at which point I'd not worry so much about the money I'm spending now only to replace them with 2-gig sticks down the line. However, in the five weeks or so I've given myself (I've told Homer Parker, the AT lead, a few weeks, I'm now setting myself the goal of end of July, giving me 5 weeks, hoping setting the date publicly, and tying it to my memory upgrade, will help me avoid finding an excuse to postpone <g>), I doubt either price will fall that far. Thus, I've got to choose between four 1-gig sticks, or two or four 2-gig sticks, at basically the prices listed above, ideally by mid-July. I've got a call to make this week. /Maybe/ I'll place the order today, locally. Someone I know said they thought they could match on-line prices thru their supplier, especially if I was able to commit to four sticks at once. I'm a bit skeptical they'll beat pricewatch, but if they do, I could well be placing the order today or anyway this week (which will mean I'll /really/ have to get studying on that AT quiz, if I keep them linked <g>). -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman in http://www.linuxdevcenter.com/pub/a/linux/2004/12/22/rms_interview.html -- [email protected] mailing list
