Messages in this thread | | | Date | Wed, 12 Jun 1996 15:20:29 +0300 | From | Riku Saikkonen <> |
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Newsgroups: linux.dev.kernel Path: rjs From: rjs@spider.compart.fi (Riku Saikkonen) Subject: Re: No atime X-Newsreader: TIN [UNIX 1.3 950824BETA PL0] Sender: rjs@isil.lloke.dna.fi (Riku Saikkonen) Lines: 41 Organization: I laureloke Message-ID: <DsvzM4.Gw7@isil.lloke.dna.fi> References: <199606030835.JAA03620@snowcrash.cymru.net> Date: Wed, 12 Jun 1996 12:20:28 GMT
Alan Cox (alan@cymru.net) wrote: >2. Someone try noatime and measure laptop battery life.
And maybe normal hard disk life too, depending on what you do...
One thing where I think this really helps is if you run a system-monitor program that reads files from /proc every 60 seconds or so. Normally this update's /'s atime (I think), leading to a hard disk write every 60 seconds or so, even if the machine is otherwise completely idle.
And I assume that hard disks last longer if you keep them idle for two hours when you don't use the machine than if you write something useless to it every minute. I imagine this is what lead to the suggestion on cold.system a while ago to put parts of the system monitor tools in the kernel (can we say bloat?)...
This particular thing could be fixed by making a small read-only root partition, but I don't doubt that there are situations (like the news server stuff someone mentioned) where this isn't possible.
So... A stupid question, maybe, coming up:
Does this noatime patch really break POSIX conformance? I.e. does it really not update the atimes at all? If it doesn't, wouldn't it be better to put the atime updates in the kernel's disk-write cache and not flush the cache if there are only atime updates to be flushed?
I have little knowledge of the internals of the kernel's disk cache mechanism, but... I guess this would require some sort of `important' flag for entries in the disk write cache. And then the buffering algorithm would decide not to flush the buffers if there's only non-important stuff in them. But if there's anything flagged as `important' there (and maybe if someone asks for a disk _read_, as the disk has to spin up then), flush the non-important stuff too.
This shouldn't break POSIX, at least not in a way that applications could notice, if a read of the atime looked at the (still unflushed) write cache before reading the (maybe obsolete) atime from the disk.
-- -=- Rjs -=- rjs@spider.compart.fi - http://isil.lloke.dna.fi/rjs/
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