Messages in this thread | | | Date | Thu, 11 Jan 2007 15:54:05 +0800 | From | Aubrey <> | Subject | Re: O_DIRECT question |
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On 1/11/07, Nick Piggin <nickpiggin@yahoo.com.au> wrote: > Andrew Morton wrote: > > On Thu, 11 Jan 2007 14:45:12 +0800 > > Aubrey <aubreylee@gmail.com> wrote: > > > > > >>>In the interim you could do the old "echo 3 > /proc/sys/vm/drop_caches" > >>>thing, but that's terribly crude - drop_caches is really only for debugging > >>>and benchmarking. > >>> > >> > >>Yes. This method can drop caches, but will fragment memory. > > > > > > That's what page reclaim will do as well. > > > > What you want is Mel's antifragmentation work, or lumpy reclaim. > > > > > >>This is > >>not what I want. I want cache is limited to a tunable value of the > >>whole memory. For example, if total memory is 128M, is there a way to > >>trigger reclaim when cache size > 16M? > > > > > > If there was, it'd "fragment memory" as well. > > > > You might get a little benefit from increasing /proc/sys/vm/min_free_kbytes, > > but not much. Some page allocation tweaks would aid that. > > > > But basically, to do this well, serious work is needed. > > OTOH, the antifragmentation stuff can also break down eventually, > especially if higher order allocations are actually in common use.
That's right. When VFS cache eat up almost all of the memory, I think no memory algorithm can help the case, including Mei's anti-fragment patch.
> > What you _really_ want to do is avoid large mallocs after boot, or use > a CPU with an mmu. I don't think nommu linux was ever intended to be a > simple drop in replacement for a normal unix kernel.
Is there a position available working on mmu CPU? Joking, :) Yes, some problems are serious on nommu linux. But I think we should try to fix them not avoid them.
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