| From: | Radosław Smogura <rsmogura(at)softperience(dot)eu> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | pgsql-hackers(at)postgresql(dot)org, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Peter Eisentraut <peter_e(at)gmx(dot)net>, Greg Stark <gsstark(at)mit(dot)edu>, Robert Haas <robertmhaas(at)gmail(dot)com>, Greg Smith <greg(at)2ndquadrant(dot)com>, Joshua Berkus <josh(at)agliodbs(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
| Subject: | Re: MMAP Buffers |
| Date: | 2011-04-17 20:09:24 |
| Message-ID: | 201104172209.24587.rsmogura@softperience.eu |
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| Lists: | pgsql-hackers |
Andres Freund <andres(at)anarazel(dot)de> Sunday 17 April 2011 20:02:11
> On Sunday 17 April 2011 19:26:31 Radosław Smogura wrote:
> > Kernel merges vm_structs. So mappings are compacted. I'm not kernel
> > specialist, but skipping memory consumption, for not compacted mappings,
> > kernel uses btrees for dealing with TLB, so it should not matter if
> > there is 100 vm_structs or 100000 vm_structs.
>
> But the CPUs TLB cache has maybe 16/256 (1lvl, 2nd) to 64/512 entries. That
> will mean that there will be cachemisses all over.
> Additionally your scheme requires flushing it regularly...
>
> Andres
I only know Phenom has 4096 entries I think and this covers 16MB of memory.
But I was taking about memory usage of struct vm_struct in kernel. I tries as
well with huge pages, but I can't write really fast allocator for this, it's
slower then malloc, maybe from different reasons.
Regards,
Radek
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