Re: [PATCH 2/4] frontswap: using vzalloc instead of vmalloc

[Johannes Weiner <hannes@cmpxchg.org>]

On Thu, Aug 04, 2011 at 09:57:30AM +0200, Michal Hocko wrote:
> On Thu 04-08-11 11:09:48, Bob Liu wrote:
> > This patch also add checking whether alloc frontswap_map memory
> > failed.
> > 
> > Signed-off-by: Bob Liu <lliubbo@gmail.com>
> > ---
> >  mm/swapfile.c |    6 +++---
> >  1 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> > index ffdd06a..8fe9e88 100644
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -2124,9 +2124,9 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
> >  	}
> >  	/* frontswap enabled? set up bit-per-page map for frontswap */
> >  	if (frontswap_enabled) {
> > -		frontswap_map = vmalloc(maxpages / sizeof(long));
> > -		if (frontswap_map)
> > -			memset(frontswap_map, 0, maxpages / sizeof(long));
> > +		frontswap_map = vzalloc(maxpages / sizeof(long));
> > +		if (!frontswap_map)
> > +			goto bad_swap;
> 
> vzalloc part looks good but shouldn't we disable frontswap rather than
> fail?

Silently dropping explicitely enabled features is not a good idea,
IMO.  But from a quick look, this seems to be actually happening as
frontswap's bitmap tests check for whether there is even a bitmap
allocated and it should essentially never do anything for real if
there isn't.

How about printing a warning as to why the swapon fails and give the
admin a choice to disable it on her own?

It's outside this patch's scope, though, just as changing the
behaviour to fail swapon is.

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