Messages in this thread | | | Date | Thu, 27 Aug 1998 14:43:31 +0200 (MET DST) | From | Bernhard Heidegger <> | Subject | Re: [PATCH] 498+ days uptime |
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>>>>> ">" == Zlatko Calusic <Zlatko.Calusic@CARNet.hr> writes:
>> Bernhard Heidegger <bheide@hyperwave.com> writes: >> >>>>> ">" == Zlatko Calusic <Zlatko.Calusic@CARNet.hr> writes: >> >> >> "H. Peter Anvin" <hpa@transmeta.com> writes: >> >> > >> >> > bdflush yes, but update is not obsolete. >> >> > >> >> > It is still needed if you want to make sure data (and metadata) >> >> > eventually gets written to disk. >> >> > >> >> > Of course, you can run without update, but then don't bother if you >> >> > lose file in system crash, even if you edited it and saved it few >> >> > hours ago. :) >> >> > >> >> > Update is very important if you have lots of RAM in your computer. >> >> > >> >> >> >> Oh. I guess my next question then is "why", as why can't this be done >> >> by kflushd as well? >> >> >> >> >> To tell you the truth, I'm not sure why, these days. >> >> >> I thought it was done this way (update running in userspace) so to >> >> have control how often buffers get flushed. But, I believe bdflush >> >> program had this functionality, and it is long gone (as you correctly >> >> noticed). >> >> IMHO, update/bdflush (in user space) calls sys_bdflush regularly. This >> function (fs/buffer.c) calls sync_old_buffers() which itself sync_supers >> and sync_inodes before it goes through the dirty buffer lust (to write >> some dirty buffers); the kflushd only writes some dirty buffers dependent >> on the sysctl parameters. >> If I'm wrong, please feel free to correct me! >>
>> You are not wrong.
>> Update flushes metadata blocks every 5 seconds, and data block every >> 30 seconds.
My version of update (something around Slakware 3.4) does the following: 1.) calls bdflush(1,0) (fs/buffer.c:sys_bdflush) which will call sync_old_buffers() and return 2.) only if the bdflush(1,0) fails (it returns < 0) it returns to the old behavior of sync()ing every 30 seconds
But case 2) should only happen on really old kernels; on newer kernels (I'm using 2.0.34) the bdflush() should never fail.
But as I told, sync_old_buffers() do: 1.) sync_supers(0) 2.) sync_inodes(0) 3.) go through dirty buffer list and may flush some buffers
Conclusion: the meta data get synced every 5 seconds and some buffers may be flushed.
>> Questions is why can't this functionality be integrated in the kernel, >> so we don't have to run yet another daemon?
Good question, but I've another one: IMHO sync_old_buffers (especially the for loop) do similar things as the kflushd. Why?? Is it possible to reduce the sync_old_buffers() routine to soemthing like: { sync_supers(0); sync_inodes(0); } ??
Bernhard
get my pgp key from a public keyserver (keyID=0x62446355) ----------------------------------------------------------------------------- Bernhard Heidegger bheide@hyperwave.com Hyperwave Software Research & Development Schloegelgasse 9/1, A-8010 Graz Voice: ++43/316/820918-25 Fax: ++43/316/820918-99 -----------------------------------------------------------------------------
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