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From: davea@quasar.wpd.sgi.com (David B. Anderson)
Newsgroups: comp.sys.sgi
Subject: Re: malloc on IRIX System V
Message-ID: <47469@sgi.sgi.com>
Date: 4 Jan 90 22:08:47 GMT
References: <9001041731.AA03346@acf8.NYU.EDU>
Sender: davea@quasar.wpd.sgi.com
Reply-To: davea@quasar.UUCP (David B. Anderson)
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 22

In article <9001041731.AA03346@acf8.NYU.EDU> kalvina@ACF8.NYU.EDU (Alan Kalvin) writes:
>
>If malloc is used to allocate an amount of memory greater or equal to
>the system page size, will the memory returned will be page-aligned?

No, not by default. And not with the libc.a malloc.

>If not, is it possible to force page-alignment?

Look at the mallinfo man page (M_GRAIN particularly).  Appropriately
configured and used, the malloc in libmalloc.a will do what you want.


Regards,
[ David B. Anderson  Silicon Graphics  (415)335-1548  davea@sgi.com ]

PS:
The traditional (before mallinfo()) way to do this is to 
a) malloc 1 page more than is needed.
b) adjust the returned pointer (upwards) to the nearest page boundary.
The extra space is ``wasted''.  Moreover, the adjusted pointer cannot
be used in a free(3) call (only the original pointer can be used with free() ).