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
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.
Ditto for the gfp_pfmemalloc_allowed function.
Prefixing with '!!' would make it safe.
NeilBrown
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