Re: [-mm][PATCH 2/4] Setup the memrlimit controller (v5)

[Andrea Righi]

Andrew Morton wrote:
> On Wed, 11 Jun 2008 19:10:40 +0200 (MEST)
> Andrea Righi <righi.andrea@xxxxxxxxx> wrote:
>
> > Balbir Singh wrote:
> > > +static int memrlimit_cgroup_write_strategy(char *buf, unsigned long long *tmp)
> > > +{
> > > +	*tmp = memparse(buf, &buf);
> > > +	if (*buf != '\0')
> > > +		return -EINVAL;
> > > +
> > > +	*tmp = PAGE_ALIGN(*tmp);
> > > +	return 0;
> > > +}
> > We shouldn't use PAGE_ALIGN() here, otherwise we limit the address space
> > to 4GB on 32-bit architectures (that could be reasonable, because this
> > is a per-cgroup limit and not per-process).
> >
> > Signed-off-by: Andrea Righi <righi.andrea@xxxxxxxxx>
> > ---
> >  mm/memrlimitcgroup.c |    4 +++-
> >  1 files changed, 3 insertions(+), 1 deletions(-)
> >
> > diff --git a/mm/memrlimitcgroup.c b/mm/memrlimitcgroup.c
> > index 9a03d7d..2d42ff3 100644
> > --- a/mm/memrlimitcgroup.c
> > +++ b/mm/memrlimitcgroup.c
> > @@ -29,6 +29,8 @@
> >  #include <linux/res_counter.h>
> >  #include <linux/memrlimitcgroup.h>
> >  
> > +#define PAGE_ALIGN64(addr) (((((addr)+PAGE_SIZE-1))>>PAGE_SHIFT)<<PAGE_SHIFT)
> > +
> >  struct cgroup_subsys memrlimit_cgroup_subsys;
> >  
> >  struct memrlimit_cgroup {
> > @@ -124,7 +126,7 @@ static int memrlimit_cgroup_write_strategy(char *buf, unsigned long long *tmp)
> >  	if (*buf != '\0')
> >  		return -EINVAL;
> >  
> > -	*tmp = PAGE_ALIGN(*tmp);
> > +	*tmp = PAGE_ALIGN64(*tmp);
> >  	return 0;
> >  }
> >  
>
> I don't beleive the change is needed.
>
> #define PAGE_ALIGN(addr)	(((addr)+PAGE_SIZE-1)&PAGE_MASK)
>
> that implementation will behaved as desired when passed a 64-bit addr?

If I'm not doing something wrong, here is what happens on my i386 box:

$ uname -m
i686
$ cat 64-bit-page-align.c
#include <stdio.h>
#include <asm/page.h>

#define PAGE_ALIGN(addr)	(((addr)+PAGE_SIZE-1)&PAGE_MASK)
#define PAGE_ALIGN64(addr) (((((addr)+PAGE_SIZE-1))>>PAGE_SHIFT)<<PAGE_SHIFT)

#define SIZE ((1ULL << 32) - 1)

int main(int argc, char **argv)
{
	unsigned long long good, bad;

	good = (unsigned long long)PAGE_ALIGN64(SIZE);
	bad = (unsigned long long)PAGE_ALIGN(SIZE);

	fprintf(stdout, "good = %llu, bad = %llu\n", good, bad);

	return 0;
}
$ gcc -O2 -o 64-bit-page-align 64-bit-page-align.c
$ ./64-bit-page-align
good = 4294967296, bad = 0
                  ^^^^^^^
On a x86_64, instead, both PAGE_ALIGN()s work as expected:

$ uname -m
x86_64
$ gcc -O2 -o 64-bit-page-align 64-bit-page-align.c
$ ./64-bit-page-align
good = 4294967296, bad = 4294967296

At least we could add something like:

#ifdef CONFIG_32BIT
#define PAGE_ALIGN64(addr) (((((addr)+PAGE_SIZE-1))>>PAGE_SHIFT)<<PAGE_SHIFT)
#else
#define PAGE_ALIGN64(addr) PAGE_ALIGN(addr)
#endif

But IMHO the single PAGE_ALIGN64() implementation is more clear.

-Andrea
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