Re: [Linux-ia64] Pagesize is different between IA32 and IA64

From: <n0ano_at_indstorage.com>
Date: 2001-11-17 02:09:19
Miyoshi-

Glad to hear that.

I thought about doing that but that would have required an extra
check, zeroing to the smaller of `obrk' or the end of the current
page.  I prefer the simplicity of just zeroing the page unless
someone can demonstrate a program that shows a measurable performance
gain from this change.

On Fri, Nov 16, 2001 at 03:17:09PM +0900, miyoshi@hpc.bs1.fc.nec.co.jp wrote:
> 
> Hi,
> 
> Thank you for your patch!
> Hideki tested it and it seems to work fine.
> 
> BTW, how about the following optimization?
> IA32-glibc's calloc can call sbrk with 4K boundary.
> When we do 4k sbrk, we do not need fully zero-ing up to 16K boundary,
> but just up to obrk.
> 
> (Think about four sbrk(-0x1000) case)
> 
> Thanks.
> 
> +asmlinkage unsigned long
> +sys32_brk(unsigned int brk)
> +{
> +	unsigned long ret, obrk;
> +	struct mm_struct *mm = current->mm;
> +
> +	obrk = mm->brk;
> +	ret = sys_brk(brk);
> +	if (ret < obrk){
> +		unsigned long to;
> +		to = (obrk < PAGE_ALIGN(ret) ? obrk : PAGE_ALIGN(ret));
> +		clear_user(ret, to-ret);
> +	}
> +	return(ret);
> +} 
> 
> 
> 
> 
> 
> > David-
> > 
> > OK, here's the patch to fix this.  I guess the only issue is that we
> > have to have Yet Another IA32 System call shim but other than that
> > the change is pretty minor.
> > 
> > PS:  Hideki, please note that this is a different, slightly better
> > patch than the one I sent you last night.  You should use this one.
> > 
> > On Tue, Nov 13, 2001 at 11:43:55PM -0700, Dugger's wrote:
> > > Never mind, I found the `calloc' code and I'm very depressed because it
> > > does indeed assume that `brk' zeros out newly allocated memory which is
> > > obviously going to create problems if `calloc' thinks the kernel has 4K
> > > pages when it really has bigger ones.
> > > 
> > > Unfortunately, this means I'll have to make an IA32 specific `brk' call that
> > > zero's out the last part of the last page currently allocated to a process.
> > > Oh well, patch to follow later.
> > > --
> > > Don Dugger
> > > n0ano@indstorage.com
> > > ----- Original Message -----
> > > From: "Dugger's" <ddugger@qwest.net>
> > > To: <davidm@hpl.hp.com>; <n0ano@indstorage.com>
> > > Cc: "Hideki Yamamoto" <hideki@hpc.bs1.fc.nec.co.jp>;
> > > <linux-ia64@linuxia64.org>
> > > Sent: Tuesday, November 13, 2001 11:16 PM
> > > Subject: Re: [Linux-ia64] Pagesize is different between IA32 and IA64
> > > 
> > > 
> > > > I'm a little confused.  From Hideki's test program the problem actually
> > > > seems
> > > > to be using `sbrk' to return memory and then allocating memory again.  The
> > > > second
> > > > time the re-allocated memory is not zeroed, e.g.:
> > > >
> > > >     p = sbrk(4096);
> > > >     q = sbrk(-4096);
> > > >     r = sbrk(4096);
> > > >
> > > > and the memory pointed to by `r' is not zeroed.  I just got through
> > > reading
> > > > the
> > > > man page for `brk' and `sbrk' and neither one specifies that newly
> > > allocated
> > > > memory is zeroed and therefore I interpret this issue as undefined
> > > behavior.
> > > > Any program that depends upon the contents of newly allocated memory is
> > > > broken.  In fact, if you compile the test program, `d.c', for IA64 and run
> > > > it it
> > > > fails.  Also, if you compile the test program for IA32 and use 1K
> > > allocation
> > > > blocks
> > > > the program fails on an IA32 machine also.
> > > >
> > > > Someone correct me if I'm wrong about this.
> > > >
> > > > PS:  I know that `calloc' is defined to zero out the allocated memory but
> > > > from
> > > > what I can tell it does this by explicitly calling `memset'.  I'm trying
> > > to
> > > > verify this
> > > > but I haven't found the `calloc' code in the `glibc' tree yet.  (The
> > > `glibc'
> > > > tree always
> > > > confuses me, if anyone can tell me exactly where to find the `calloc' code
> > > > I'd
> > > > appreciate it :-)
> > > > --
> > > > Don Dugger
> > > > n0ano@indstorage.com
> > > > ----- Original Message -----
> > > > From: "David Mosberger" <davidm@hpl.hp.com>
> > > > To: <n0ano@indstorage.com>
> > > > Cc: "Hideki Yamamoto" <hideki@hpc.bs1.fc.nec.co.jp>;
> > > > <linux-ia64@linuxia64.org>
> > > > Sent: Monday, November 12, 2001 4:58 PM
> > > > Subject: Re: [Linux-ia64] Pagesize is different between IA32 and IA64
> > > >
> > > >
> > > > > But I think the page size problem with brk() is real and can be fixed
> > > > > quite easily.  If I understood correctly, the problem is that doing
> > > > > something along the lines of:
> > > > >
> > > > > x = ALIGN_TO_4K(sbrk(8192));
> > > > > memset(x, 0xff, 4096);
> > > > > brk(x);
> > > > > brk(x+4096);
> > > > >
> > > > > might preserve the contents of the page at X on under the ia32
> > > > > subsystem of ia64 when in fact it should be cleared to zero.
> > > > >
> > > > > Would you be able/interested into looking into this?
> > > > >
> > > > > --david
> > > > >
> > > >
> > > 
> > > 
> > > _______________________________________________
> > > Linux-IA64 mailing list
> > > Linux-IA64@linuxia64.org
> > > http://lists.linuxia64.org/lists/listinfo/linux-ia64
> > 
> > -- 
> > Don Dugger
> > "Censeo Toto nos in Kansa esse decisse." - D. Gale
> > n0ano@indstorage.com
> > Ph: 303/652-0870x117
> > 
> > diff -aur kernel-bigsur-ref/arch/ia64/ia32/ia32_entry.S kernel-bigsur/arch/ia64/ia32/ia32_entry.S
> > --- kernel-bigsur-ref/arch/ia64/ia32/ia32_entry.S	Tue Sep 25 19:40:29 2001
> > +++ kernel-bigsur/arch/ia64/ia32/ia32_entry.S	Wed Nov 14 21:07:28 2001
> > @@ -209,7 +209,7 @@
> >  	data8 sys32_pipe
> >  	data8 sys32_times
> >  	data8 sys32_ni_syscall	  /* old prof syscall holder */
> > -	data8 sys_brk		  /* 45 */
> > +	data8 sys32_brk		  /* 45 */
> >  	data8 sys_setgid	/* 16-bit version */
> >  	data8 sys_getgid	/* 16-bit version */
> >  	data8 sys32_signal
> > diff -aur kernel-bigsur-ref/arch/ia64/ia32/sys_ia32.c kernel-bigsur/arch/ia64/ia32/sys_ia32.c
> > --- kernel-bigsur-ref/arch/ia64/ia32/sys_ia32.c	Tue Sep 25 19:40:29 2001
> > +++ kernel-bigsur/arch/ia64/ia32/sys_ia32.c	Thu Nov 15 07:29:24 2001
> > @@ -68,6 +68,7 @@
> >  
> >  /* forward declaration: */
> >  asmlinkage long sys32_mprotect (unsigned int, unsigned int, int);
> > +asmlinkage unsigned long sys_brk(unsigned long);
> >  
> >  static int
> >  nargs (unsigned int arg, char **ap)
> > @@ -2123,6 +2124,7 @@
> >  	      default:
> >  		return -EINVAL;
> >  	}
> > +	return -EINVAL;
> >  }
> >  
> >  /*
> > @@ -3376,6 +3378,19 @@
> >  		ret = PER_LINUX;
> >  	return ret;
> >  }
> > +
> > +asmlinkage unsigned long
> > +sys32_brk(unsigned int brk)
> > +{
> > +	unsigned long ret, obrk;
> > +	struct mm_struct *mm = current->mm;
> > +
> > +	obrk = mm->brk;
> > +	ret = sys_brk(brk);
> > +	if (ret < obrk)
> > +		clear_user(ret, PAGE_ALIGN(ret) - ret);
> > +	return(ret);
> > +} 
> >  
> >  #ifdef	NOTYET  /* UNTESTED FOR IA64 FROM HERE DOWN */
> >  
> > 
> > _______________________________________________
> > Linux-IA64 mailing list
> > Linux-IA64@linuxia64.org
> > http://lists.linuxia64.org/lists/listinfo/linux-ia64
> > 
> 
> _______________________________________________
> Linux-IA64 mailing list
> Linux-IA64@linuxia64.org
> http://lists.linuxia64.org/lists/listinfo/linux-ia64

-- 
Don Dugger
"Censeo Toto nos in Kansa esse decisse." - D. Gale
n0ano@indstorage.com
Ph: 303/652-0870x117
Received on Fri Nov 16 07:10:17 2001

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