Re: Coalescing memory on Sun

Thomas Tornblom <no_at_spam.please> writes:

> andreyNSPAM_at_bookexchange.net (NetComrade) writes:
>
> > Can memory get fragmented on Unix, therefore no big chunk being able
> > allocated?
> > If yes, is there are a way to defragment it?
> > ---------------
> > Andrey Dmitriev eFax: (978) 383-5892 Daytime: (917) 373-5417
> > AOL: NetComrade ICQ: 11340726 remove NSPAM to email
> >
>

[snip]

I hate being wrong ;-)

I got a reply from someone that obviously knows more abot this than me...

>No, memory can't be "fragmented". (In fact it is almost always fragmented).

Actually, considering the original poster cross-posted to a database newsgroup the answer is "yes, it can". ISM uses large pages for database performance. 4M pages have to consist of physically contiguous, 4MB-aligned 8k pages (let's assume sun4u here, shall we?). So if the system's been running for a while and a database asks for ISM it may or may not get 4MB pages due to memory fragmentation. The program won't fail but it will run slower due to higher TLB miss rate, etc.

You're answer is correct if ISM is not involved.

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Thomas Tornblom          Tel: +46 8 623 9100   E-mail: Thomas.Tornblom_at_Sun.SE
Sun Microsystems AB      Fax: +46 8 623 9102