On Tue, 2011-04-26 at 21:15 +1000, NeilBrown wrote:
> On Tue, 26 Apr 2011 08:36:43 +0100 Mel Gorman <mgorman@xxxxxxx> wrote:
>
> > +bool gfp_pfmemalloc_allowed(gfp_t gfp_mask)
> > +{
> > + return gfp_to_alloc_flags(gfp_mask) & ALLOC_PFMEMALLOC;
> > +}
> > +
> > static inline struct page *
> > __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> > struct zonelist *zonelist, enum zone_type high_zoneidx,
> > @@ -2202,8 +2211,16 @@ nopage:
> > got_pg:
> > if (kmemcheck_enabled)
> > kmemcheck_pagealloc_alloc(page, order, gfp_mask);
> > - return page;
> >
> > + /*
> > + * page->pfmemalloc is set when the caller had PFMEMALLOC set or is
> > + * been OOM killed. The expectation is that the caller is taking
> > + * steps that will free more memory. The caller should avoid the
> > + * page being used for !PFMEMALLOC purposes.
> > + */
> > + page->pfmemalloc = (alloc_flags & ALLOC_PFMEMALLOC);
> > +
> > + return page;
>
> Linus doesn't seem to be a fan of this construct:
> https://lkml.org/lkml/2011/4/1/255
>
There is confusion around this topic. Andrew prefers bool for true/false
values and it's self-documenting. I tend to prefer it myself for
readability and there is a slow conversion in the VM from
ints-used-as-bools to bools and my understanding of bool is that any
non-zero value will be treated as true (just as it is for int).
> pfmemalloc is a bool, and the value on the right is either 0 or 0x1000.
>
> If bool happens to be typedefed to 'char' or even 'short', pfmemalloc would
> always be set to 0.
It is typedeffed as _Bool though which I thought was able to handle the
cast appropriately or is that wrong?
> Ditto for the gfp_pfmemalloc_allowed function.
>
> Prefixing with '!!' would make it safe.
>
Will do that to avoid any oddities. Thanks
--
Mel Gorman
SUSE Labs
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